Process creation and termination monitors for use in a distributed message-based operating system

A distributed data processing system is provided comprising a plurality of processes which communicate with one another using messages. When a process is created or terminated anywhere in the system a notification message may be requested. Such requests may be made regarding different organizational levels of the system, for example the entire system, one node, or a group of related processes.

RELATED INVENTIONS 
The present invention is related to the following inventions, all filed on 
May 6, 1985, and all assigned to the assignee of the present invention: 
1. Title: Nested Contexts in a Virtual Single Machine 
Inventors: Andrew Kun, Frank Kolnick, Bruce Mansfield 
Ser. No.: 07/270,437 filed Nov. 7, 1988, a continuation of Ser. No. 739,903 
(now abandoned) 
2. Title: Computer System With Data Residence Transparency and Data Access 
Transparency 
Inventors: Andrew Kun, Frank Kolnick, Bruce Mansfield 
Ser. No.: 07/300,697 filed Jan. 19, 1989, a continuation of Ser. No. 
110,614 (now abandoned) which was a continuation of Ser. No. 730,929 (now 
abandoned) 
3. Title: Network Interface Module With Minimized Data Paths 
Inventors: Bernhard Weisshaar, Michael Barnea 
Ser. No.: 730,621, now U.S. Pat. No. 4,754,395 
4. Title: Method of Inter-Process Communication in a Distributed Data 
Processing System 
Inventors: Bernhard Weisshaar, Andrew Kun, Frank Kolnick, Bruce Mansfield 
Ser. No.: 730,892, now U.S. Pat. No. 4,694,396 
5. Title: Logical Ring in a Virtual Single Machine 
Inventor: Andrew Kun, Frank Kolnick, Bruce Mansfield 
Ser. No.: 730,923 (now abandoned) and Ser. No. 183,469, filed Apr. 15, 1988 
(continuation) 
6. Title: Virtual Single Machine With Message-Like Hardware Interrupts and 
Processor Exceptions 
Inventors: Andrew Kun, Frank Kolnick, Bruce Mansfield 
Ser. No.: 730,922 
The present invention is also related to the following inventions, all 
filed on even date herewith, and all assigned to the assignee of the 
present invention: 
7. Title: Computer Human Interface Comprising User-Adjustable Window for 
Displaying or Printing Information 
Inventor: Frank Kolnick 
Ser. No.: 07/335,092 filed May 17, 1989, a continuation of Ser. No. 000,625 
(now abandoned) 
8. Title: Computer Human Interface With Multi-Application Display 
Inventor: Frank Kolnick 
Ser. No.: 000,620 
9. Title: Object-Oriented Software Architecture Supporting Input/Output 
Device Independence 
Inventor: Frank Kolnick 
Ser. No.: 07/361,738 filed June 2, 1989, a continuation of Ser. No. 000,619 
(now abandoned) 
10. Title: Self-Configuration of Nodes in a Distributed Message-Based 
Operating System 
Inventors: Gabor Simor 
Ser. No.: 000,621 
11. Title: Computer Human Interface With Multiple Independent Active 
Pictures and Windows 
Inventors: Frank Kolnick 
Ser. No.: 07/274,674 filed Nov. 21, 1988, a continuation of Ser. No. 
000,626 (now abandoned) 
TECHNICAL FIELD 
This invention relates generally to digital data processing, and, in 
particular, to an operating system in which a notification message may be 
requested whenever a specified process is created or terminated. 
BACKGROUND OF THE INVENTION 
The present invention is implemented in a distributed data processing 
system--that is, two or more data processing systems which are capable of 
functioning independently but which are so coupled as to send and receive 
messages to and from one another. 
Local Area Network (LAN) is an example of a distributed data processing 
system. A typical LAN comprises a number of autonomous data processing 
"nodes", each comprising at least a processor and memory. Each node is 
capable of conducting data processing operations independently. In 
addition, each node is coupled (by appropriate means such as a twisted 
wire pair, coaxial cable, fiber optic cable, etc.) to a network of other 
nodes which may be, for example, a loop, star, tree, etc., depending upon 
the design considerations. 
As mentioned above, the present invention finds utility in such a 
distributed data processing system, since there is a need in such a system 
for processes which are executing or which are to be executed in the 
individual nodes to share data and to communicate data among themselves. 
A "process", as used within the present invention, is defined as a 
self-contained package of data and executable procedures which operate on 
that data, comparable to a "task" in other known systems. Within the 
present invention a process can be thought of as comparable to a 
subroutine in terms of size, complexity, and the way it is used. The 
difference between processes and subroutines is that processes can be 
created and destroyed dynamically and can execute concurrently with their 
creator and other "subroutines". 
Within a process, as used in the present invention, the data is totally 
private and cannot be accessed from the outside, i.e., by other processes. 
Processes can therefore be used to implement "objects", "modules", or 
other higher-level data abstractions. Each process executes sequentially. 
Concurrency is achieved through multiple processes, possibly executing on 
multiple processors. 
Every process in the distributed data processing system of the present 
invention has a unique identifier (PID) by which it can be referenced. The 
PID is assigned by the system when the process is created, and it is used 
by the system to physically locate the process. 
Every process also has a non-unique, symbolic "name", which is a 
variable-length string of characters. In general, the name of a process is 
known system-wide. To restrict the scope of names, the present invention 
utilizes the concept of a "context". 
A "context" is simply a collection of related processes whose names are not 
known outside of the context. Contexts partition the name space into 
smaller, more manageable subsystems. They also "hide" names, ensuring that 
processes contained in them do not unintentionally conflict with those in 
other contexts. 
A process in one context cannot explicitly communicate with, and does not 
know about, processes inside other contexts. All interaction across 
context boundaries must be through a "context process", thus providing a 
degree of security. The context process often acts as a switchboard for 
incoming messages, rerouting them to the appropriate sub-processes in its 
context. 
A context process behaves like any other process and additionally has the 
property that any processes which it creates are known only to itself and 
to each other. Creation of the process constitutes definition of a new 
context with the same name as the process. 
Any process can create context processes. Each new context thus defined is 
completely contained inside the context in which it was created and 
therefore is shielded from outside reference. This "nesting" allows the 
name space to be structured hierarchically to any desired depth. 
Conceptually, the highest level in the hierarchy is the system itself, 
which encompasses all contexts. Nesting is used in top-down design to 
break a system into components or "layers", where each layer is more 
detailed than the preceding one. This is analogous to breaking a task down 
into subroutines, and in fact many applications which are single tasks on 
known systems may translate to multiple processes in nested contexts. 
A "message" is a buffer containing data which tells a process what to do 
and/or supplies it with information it needs to carry out its operation. 
Each message buffer can have a different length (up to 64 kilobytes). By 
convention, the first field in the message buffer defines the type of 
message (e.g., "read", "print", "status", "event", etc.). 
Messages are queued from one process to another by name or PID. Queuing 
avoids potential synchronization problems and is used instead of 
semaphores, monitors, etc. The sender of a message is free to continue 
after the message is sent. When the receiver attempts to get a message, it 
will be suspended until one arrives if none are already waiting in its 
queue. Optionally, the sender can specify that it wants to wait for a 
reply and is suspended until that specific message arrives. Messages from 
any other source are not dequeued until after that happens. 
Within the present invention, messages are the only way for two processes 
to exchange data. There is no concept of a "global variable". Shared 
memory areas are not allowed, other than through processes which 
essentially "manage" each area by means of messages. Messages are also the 
only form of dynamic memory that the system handles. A request to allocate 
memory therefore returns a block of memory which can be used locally by 
the process but can also be transmitted to another process. 
Messages provide the mechanism by which hardware transparency is achieved. 
A process located anywhere in the system may send a message to any other 
process anywhere else in the system (even on another processor) if it 
knows the process name. This means that processes can be dynamically 
distributed across the system at any time to gain optimal throughput 
without changing the processes which reference them. Resolution of 
destinations is done by searching the process name space. 
The context nesting level determines the "scope of reference" when sending 
messages between processes by name. From a given process, a message may be 
sent to all processes at its own level (i.e., in the same context) and 
(optionally) to any arbitrary higher level. The contexts are searched from 
the current context upward until a match is found. All processes with the 
given name at that level are then sent a copy of the message. A process 
may also send a message to itself or to its parent (the context process) 
without knowing either name explicitly, permitting multiple instances of a 
process to exist in different contexts, with different names. 
Sending messages by PID obviates the need for a name search and ignores 
context boundaries. This is the most efficient method of communicating. 
In known data processing systems a process control block (PCB) is used to 
describe various attributes and the status of processes, including the 
status of resources used by the processes. Examples of such resources are 
files, data storage devices, I/O devices, ports, etc. 
The operating system of the present invention utilizes PCB's too, but they 
do not have to keep track of the status of processes or resources used by 
the processes, thus enabling the system to be more modular and 
reconfigurable. 
However, it is still desirable to provide the capability of monitoring the 
status of processes within the operating system of the present invention, 
and in particular the fact that a process has been created or terminated. 
There is a significant need to be able to provide within a data processing 
operating system the ability for a process to request to be notified when 
a designated process has been created and/or terminated. In addition, 
there is a need for such notification to occur within several organization 
levels, such as one context of processes, one node, or an entire network. 
Further, there is a need to be able to request suspension of the process in 
addition to notification of the creation of or termination of the process. 
BRIEF SUMMARY OF INVENTION 
Accordingly, it is an object of the present invention to provide a data 
processing system having an improved operating system. 
It is also an object of the present invention to provide an improved data 
processing system having an operating system which allows a process to 
request notification when a particular process has been created and/or 
terminated within a designated portion of the data processing system. 
It is another object of the present invention to provide a distributed data 
processing system having an operating system which allows a first process 
on one node to request notification when a second process on the same or 
different node has been created and/or terminated. 
It is yet another object of the present invention to provide a distributed 
data processing system having an operating system in which notification is 
generated to requesting processes located in a plurality of nodes if and 
when a particular process has been created and/or terminated. 
It is still another object of the present invention to provide a 
distributed data processing system having an operating system in which a 
process manager process may set a process creation monitor and/or a 
process termination monitor regarding the creation and/or termination of 
an identified process. 
It is a further object of the present invention to provide a distributed 
data processing system having an operating system in which a process 
manager process may set a process creation monitor and/or a process 
termination monitor regarding the creation and/or termination of an 
identified process only upon certain conditions. 
It is another object of the present invention to provide a distributed data 
processing system having an operating system in which a process manager 
process may be requested to release a process creation monitor and/or a 
process termination trap. 
It is still another object of the present invention to provide a 
distributed data processing system having an operating system in which a 
process manager process may be requested to release or not to release 
automatically a process creation/termination monitor after the first 
identified process has been created/terminated. 
These and other objects are achieved in accordance with a preferred 
embodiment of the invention by providing, in a distributed data processing 
system comprising a plurality of interconnected nodes, the system 
comprising a plurality of processes, the processes communicating with one 
another by means of messages, a method of providing a notification message 
when a process is created on one of the nodes, the method comprising the 
steps of a) providing a process manager process on such one node, and b) 
providing a request to the process manager process to generate a 
notification message whenever a process is created on such one node.

OVERVIEW OF COMPUTER SYSTEM 
With reference to FIG. 1, a distributed computer configuration is shown 
comprising multiple nodes 2-7 (nodes) loosely coupled by a local area 
network (LAN) 1. The number of nodes which may be connected to the network 
is arbitrary and depends upon the user application. Each node comprises at 
least a processor and memory, as will be discussed in greater detail with 
reference to FIG. 2 below. In addition, each node may also include other 
units, such as a printer 8, operator display module (ODM) 9, mass memory 
module 13, and other I/O device 10. 
With reference now to FIG. 2, a multiple-network distributed computer 
configuration is shown. A first local area network LAN 1 comprises several 
nodes 2,4 and 7. LAN 1 is coupled to a second local area network 51 (LAN 
2) by means of an Intelligent Communications Module (ICM) 50. The 
Intelligent Communications Module provides a link between the LAN and 
other networks and/or remote processors (such as programmable 
controllers). 
LAN 2 may comprise several nodes (not shown) and may operate under the same 
LAN protocol as that of the present invention, or it may operate under any 
of several commercially available protocols, such as Ethernet; MAP, the 
Manufacturing Automation Protocol of General Motors Corp.; Systems Network 
Architecture (SNA) of International Business Machines, Inc.; SECS-II; etc. 
Each ICM 50 is programmable for carrying out one of the above-mentioned 
specific protocols. In addition, the basic processing module of the node 
itself can be used as an intelligent peripheral controller (IPC) for 
specialized devices. 
LAN 1 is additionally coupled to a third local area network 53 (LAN 2) via 
ICM 52. A process controller 55 is also coupled to LAN 1 via ICM 54. 
A representative node N (7, FIG. 2) comprises a processor 24 which, in a 
preferred embodiment, is a processor from the Motorola 68000 family of 
processors. Each node further includes a read only memory (ROM) 28 and a 
random access memory (RAM) 26. In addition, each node includes a Network 
Interface Module (NIM) 21, which connects the node to the LAN, and a Bus 
Interface 29, which couples the node to additional devices within a node. 
While a minimal node is capable of supporting two peripheral devices, such 
as an Operator Display Module (ODM) 41 and an I/O Module 44, additional 
devices (including additional processors, such as processor 27) can be 
provided within a node. Other additional devices may comprise, for 
example, a printer 42, and a mass-storage module 43 which supports a hard 
disk and a back-up device (floppy disk or streaming tape drive). 
The Operator Display Module 41 provides a keyboard and screen to enable an 
operator to input information and receive visual information. 
While a single node may comprise all of the above units, in the typical 
user application individual nodes will normally be dedicated to 
specialized functions. For example, one or more mass storage nodes may be 
set up to function as data base servers. There may also be several 
operator consoles and at least one node for generating hard-copy printed 
output. Either these same nodes, or separate dedicated nodes, may execute 
particular application programs. 
The system is particularly designed to provide an integrated solution for 
factory automation, data acquisition, and other real-time applications. As 
such, it includes a full complement of services, such as a graphical 
output, windows, menus, icons, dynamic displays, electronic mail, event 
recording, and file management. Software development features include 
compilers, a window-oriented editor, a debugger, and 
performance-monitoring tools. 
Local Area Network 
The local area network, as depicted in either FIG. 1 or FIG. 2, ties the 
entire system together and makes possible the distributed virtual machine 
model described below. The LAN provides high throughput, guaranteed 
response, reliability, and low entry cost. The LAN is also autonomous, in 
the sense that all system and applications software is unaware of its 
existence. For example, any Network Interface Module (e.g. NIM 21, FIG. 2) 
could be replaced without rewriting any software other than that which 
directly drives it. 
The LAN interconnection medium may be twisted-pair or coaxial cable. Two 
channels (logically, two distinct networks) may be provided for 
reliability and for increased throughput. 
The LAN architecture is a logical ring, in which an electronic "token" is 
constantly passed from node to node at high speed. The current holder of 
the token may use it to send a "frame" of data or may pass it on to the 
next node in the ring. The NIM only needs to know the logical address and 
status of its immediately succeeding neighbor. The NIM's responsibility is 
limited to detecting the failure of that neighbor or the inclusion of a 
new neighbor. In general, adjustment to failed or newly added nodes is 
automatic. 
The network interface maps directly into the processor's memory. Data 
exchange occurs through a dual-ported buffer pool which contains a linked 
list of pending "frames". Logical messages, which vary in length, are 
broken into fixed-size frames for transmission and are re-assembledby the 
receiving NIM. Frames are sequence-numbered for this purpose. If a frame 
is not acknowledged within a short period of time, it is retransmitted a 
number of times before being treated as a failure. 
As described above with reference to FIG. 2, the LAN may be connected to 
other LAN's operating under the same LAN protocol via so-called 
"bridgeways", or it may be connected to other types of LAN's via 
"gateways". 
Software Model 
The computer operating system of the present invention operates upon 
processes, messages, and contexts, as such terms are defined herein. Thus 
this operating system offers the programmer a hardware abstraction, rather 
than a data or control abstraction. 
Processes are referenced without regard to their physical location via a 
small set of message-passing primitives. As mentioned earlier, every 
process has both a unique system-generated identifier and a not 
necessarily unique name assigned by the programmer. The identifier 
provides quick direct access, while the name has a limited scope and 
provides symbolic, indirect access. 
With reference to FIG. 3, an architectural model of the present invention 
is shown. The bottom, or hardware, layer 63 comprises a number of 
processors 71-76, as described above. The processors 71-76 may exist 
physically within one or more nodes. The top, or software, layer 60 
illustrates a number of processes P1-P10 which send messages m1-m6 to each 
other. The middle layer 61, labelled "virtual machine", isolates the 
hardware from the software, and it allows programs to be written as if 
they were going to be executed on a single processor. Conversely, programs 
can be distributed across multiple processors without having been 
explicitly designed for that purpose. 
The Virtual Machine 
As discussed earlier, a "process" is a self-contained package of data and 
executable procedures which operate on that data. The data is totally 
private and cannot be accessed by other processes. There is no concept of 
shared memory within the present invention. Execution of a process is 
strictly sequential. Multiple processes execute concurrently and must be 
scheduled by the operating system. The processes can be re-entrant, in 
which case only one copy of the code is loaded even if multiple instances 
are active. 
Every process has a unique "process identifier number" (PID) by which it 
can be referenced. The PID is assigned by the system when the process is 
created and remains in effect until the process terminates. The PID 
assignment contains a randomizing factor which guarantees that the PID 
will not be re-used in the near future. The contents of the PID are 
irrelevant to the programmer but are used by the virtual machine to 
physically locate the process. A PID may be thought of as a "pointer" to a 
process. 
Every process also has a "name" which is a variable-length string of 
characters assigned by the programmer. A name need not be unique, and this 
ambiguity may be used to add new services transparently and to aid in 
fault-tolerance. 
FIG. 4 illustrates that the system-wide name space is partitioned into 
distinct subsets by means of "contexts" identified by reference numerals 
90-92. A context is simply a collection of related processes whose names 
are not known outside of the context. Context 90, for example, contains 
processes A, a, a, b, c, d, and e. Context 91 contains processes B, a, b, 
c, and f. And context 92 contains processes C, a, c, d, and x. 
One particular process in each context, called the "context process", is 
known both within the context and within the immediately enclosing one 
(referred to as its "parent context"). In the example illustrated in FIG. 
4, processes A-C are context processes for contexts 90-92, respectively. 
The parent context of context 91 is context 90, and the parent context of 
context 92 is context 91. Conceptually, the context process is located on 
the boundary of the context and acts as a gate into it. 
Processes inside context 92 can reference any processes inside contexts 90 
and 91 by name. However, processes in context 91 can only access processes 
in context 92 by going through the context process C. Processes in context 
90 can only access processes in context 92 by going through context 
processes B and C. 
The function of the context process is to filter incoming messages and 
either reject them or reroute them to other processes in its context. 
Contexts may be nested, allowing a hierarchy of abstractions to be 
constructed. A context must reside completely on one node. The entire 
system is treated as an all-encompassing context which is always present 
and which is the highest level in the hierarchy. In essence, contexts 
define localized protection domains and greatly reduce the chances of 
unintentional naming conflicts. 
If appropriate, a process inside one context can be "connected" to one 
inside another context by exchanging PID's, once contact has been 
established through one or the other of the context processes. Most 
process servers within the present invention function that way. Initial 
access is by name. Once the desired function (such as a window or file) is 
"opened", the user process and the service communicate directly via PID's. 
A "message" is a variable-length buffer (limited only by the processor's 
physical memory size) which carries information between processes. A 
header, inaccessible to the programmer, contains the destination name and 
the sender s PID. By convention, the first field in a message is a 
null-terminated string which defines the type of message (e.g., "read", 
"status", etc.) Messages are queued to the receiving process when they are 
sent. Queuing ensures serial access and is used in preference to 
semaphores, monitors, etc. 
Messages provide the mechanism by which hardware transparency is achieved. 
A process located anywhere in the virtual machine can send a message to 
any other process if it knows its name. Transparency applies with some 
restrictions across bridgeways (i.e., the interfaces between LAN's 
operating under identical network protocols) and, in general, not at all 
across gateways (i.e., the interfaces between LAN's operating under 
different network protocols) due to performance degradation. However, they 
could so operate, depending upon the required level of performance. 
Inter-Process Communication 
All inter-process communication is via messages. Consequently, most of the 
virtual machine primitives are concerned with processing messages. The 
virtual machine kernel primitives are the following: 
ALLOC--requests allocation of a (message) buffer of a given size. 
FREE--requests deallocation of a given message buffer. 
PUT--end a message to a given destination (by name or PID). 
GET--wait for and dequeue the next incoming message, optionally from a 
specific process (by PID). 
FORWARD--pass a received message through to another process. 
CALL--send a message, then wait for and dequeue the reply. 
REPLY--send a message to the originator of a given message. 
ANY MSG--returns "true" if the receive queue is not empty, else returns 
"false"; optionally, checks if any messages from a specific PID are 
queued. 
To further describe the function of the kernel primitives, ALLOC handles 
all memory allocations. It returns a pointer to a buffer which can be used 
for local storage within the process or which can be sent to another 
process (via PUT, etc.). ALLOC never "fails", but rather waits until 
enough memory is freed to satisfy the request. 
The PUT primitive queues a message to another process. The sending process 
resumes execution as soon as the message is queued. 
FORWARD is used to quickly reroute a message but maintain information about 
the original sender (whereas PUT always makes the sending process the 
originator of the message). 
REPLY sends a message to the originator of a previously received message, 
rather than by name or PID. 
CALL essentially implements remote subroutine invocations, causing the 
caller to suspend until the receiver executes a REPLY. Subsequently, the 
replied message is dequeued out of sequence, immediately upon arrival, and 
the caller resumes execution. 
The emphasis is on concurrency, so that as many processes as possible are 
executed in parallel. Hence neither PUT nor FORWARD waits for the message 
to be delivered. Conversely. GET suspends a process until a message 
arrives and dequeues it in one operation. The ANY.sub.-- MSG primitive is 
provided so that a process may determine whether there is anything of 
interest in the queue before committing itself to a GET. 
With reference now to FIG. 5, the relationship of external events to 
process will be described. The virtual machine 61 makes devices look like 
processes. For example, when an interrupt occurs in an external device 
101, the virtual machine kernel 61 queries an interrupt massage 103 to a 
specific process 104, known as an "external event service process" (EESP), 
functioning as the device manager. For efficiency, the message is 
pre-allocated once and circulates between the EESP and the kernel. The 
message contains just enough information to indicate the occurrence of the 
event. The EESP performs all hardward-specific functions related to the 
event, such as setting control registers, moving data 105 to a user 
process 106, transmitting "Read" messages from the user process 106, etc., 
and then "releasing" the interrupt. 
To become an EESP, a process issues a "connect" primitive specifying the 
appropriate device register(s). It must execute a "disconnect" before it 
exits. Device-independence is achieved by making the message protocol 
between EESP's and applications processes the same wherever possible. 
When a message is sent by name, the destination process must be found in 
the name space. The search path is determined by the nesting of the 
contexts in which the sending process resides. From a given process, a 
message can be sent to all processes in its own context or (optionally) to 
those in any higher context. Refer to FIG. 6. The contexts are searched 
from the current one upward until a match is found or until the system 
context is reached. All processes with the same name in that context are 
then queued a copy of the message. 
For example, with reference to FIG. 6, assume that in context 141 process y 
sends a message to ALL processes by the name x. Process y first searches 
within its own context 141 but finds no process x. The process y searches 
within the next higher context 131 (its parent context) but again finds no 
process x. Then process y searches within the next higher context 110 and 
finds a process x, identified by reference numeral 112. Since it is the 
only process x in context 110, it is the only recipient of the message 
from process y. 
If process a in context 131 sends a message to ALL processes by the name x, 
it first searches within its own context 131 and, finding no processes x 
there, it then searches within context 110 and finds process x (112). 
Assume that process b in context 131 sends a message to ALL processes by 
the name A. It would find process A (111) in context 110, as well as 
process A (122) which is the context process for context 121. 
A process may also send a message to itself or to its context process 
without knowing either name explicitly. 
The concept of a "logical ring" (analogous to a LAN) allows a message to be 
sent to the NEXT process in the system with a given name. The message goes 
to exactly one process in the sender's context, if such a process exists. 
Otherwise the parent context is searched. 
The virtual machine guarantees that each NEXT transmission will reach a 
different process and that eventually a transmission will be sent to the 
logically "first" process (the one that sent the original message) in the 
ring, completing the loop. In other words, all processes with the same 
name at the same level can communicate with each other without knowing how 
many there are or where they are located. The logical ring is essential 
for distributing services such as a data base. The ordering of processes 
in the ring is not predictable. 
For example, if process a (125) in context 121 sends a message to process a 
using the NEXT primitive, the search finds a first process a (124) in the 
same context 121. Process a (124) is marked as having received the 
message, and then process a (124) sends the message on to the NEXT process 
a (123) in context 121. Process a (123) is marked as having received the 
message, and then it sends the message on to the NEXT process a, which is 
the original sender process a (125), which knows not to send it further 
on, since it's been marked as having already received the message. 
Sending messages directly by PID obviates the need for a name search and 
ignores context boundaries. This is known as the mode of transmission and 
is the most efficient. For example, process A (111) sends a message in the 
DIRECT mode to process y in context 141. 
If a process sends a message in the LOCAL transmission mode, it sends it 
only to a process having the given name in the sender's own context. 
In summary, including the DIRECT transmission mode, there are five 
transmission modes which can be used with the PUT, FORWARD, and CALL 
primitives: 
ALL--to all processes with the given name in the first context which 
contains that name, starting with the sender's context and searching 
upwards through all parent contexts. 
LOCAL--to all processes with the given name in the sender's context only. 
NEXT--to the next process with the given name in the same context as the 
sender, if any; otherwise it searches upwards through all parent contexts 
until the name is found. 
LEVEL--sends to "self" (the sending process) or to "context" (the context 
process corresponding to the sender's context); "self" cannot be used with 
CALL primitive. 
DIRECT--sent by PID. 
Messages are usually transmitted by queueing a pointer to the buffer 
containing the message. A message is only copied when there are multiple 
destinations or when the destination is on another node. 
Operating System 
The operating system of the present invention consists of a kernel, which 
implements the primitives described above, plus a set of processes which 
provide process creation and termination, time management (set time, set 
alarm, etc.) and which perform node start-up and configuration. Drivers 
for devices are also implemented as processes (EESP's), as described 
above. This allows both system services and device drivers to be added or 
replaced easily. The operating system also supports swapping and paging, 
although both are invisible to applications software. 
Unlike known distributed computer systems, that used in the present 
invention does not use a distinct "name server" process to resolve names. 
Name searching is confined to the kernel, which has the advantage of being 
much faster. 
A minimal bootstrap program resides permanently (in ROM) on every node, 
e.g. ROM 28 in node N of FIG. 2. The bootstrap program executes 
automatically when a node is powered up and begins by performing basic 
on-board diagnostics. It then attempts to find and start an initial system 
code module. The module is sought on the first disk drive on the node, if 
any. If there isn't a disk, and the node is on the LAN, a message will be 
sent out requesting the module. Failing that, the required software must 
be resident in ROM. The initialization program of the kernel sets up all 
of the kernel's internal tables and then calls a predefined entry point of 
the process. 
In general, there exists a template file describing the initial software 
and hardware for each node in the system. The template defines a set of 
initial processes (usually one per service) which are scheduled 
immediately after the node start-up. These processes then start up their 
respective subsystems. A node configuration service on each node sends 
configuration messages to each subsystem when it is being initialized, 
informing it of the devices it owns. Thereafter, similar messages are sent 
whenever a new device is added to the node or a device fails or is removed 
from the node. 
Thus there is no well-defined meaning for "system up" or "system down"--as 
long as any node is active, the system as a whole may be considered to be 
"up". Nodes can be shut down or started up dynamically without affecting 
other nodes on the network. The same principle applies, in a limited 
sense, to peripherals. Devices which can identify themselves with regard 
to type, model number, etc. can be added or removed without operator 
intervention. 
Standard Message Format 
FIG. 7 illustrates the standard format of a message in the distributed data 
processing system of the type described herein. The message format 
comprises a message i.d. portion 288, one or more "triples" 289 and 290, 
and an end-of-message portion 292. Each "triple" comprises a group of 
three fields, such as fields 293-295. The first field 293 of the first 
triple 289 specifies that a Process Creation Monitor (CRTM) has to be set. 
In the second triple 290 the first field 296 specifies that the data field 
represents the name of the process to be acted upon, such as the process 
whose creation is to be monitored. The second field 297 gives the size of 
the data field. The third field 298 is the data field. A message can have 
any number of "triples". 
As presently implemented, portion 288 is 16 bytes in length, field 296 is 4 
bytes, field 297 is 4 bytes, field 298 is variable in length, and EOM 
portion 160 is 4 bytes. 
As shown in FIG. 7, the message i.d. portion 288 describes a "SET" command, 
and field 298 names a process. When the message is sent by the requesting 
process to a Process Manager Process, message portion 291 is empty, but 
when the message is returned to the requesting process by the PMP, message 
portion 290 will contain the process "connector". The process connector 
identifies the designated process by processor identification number (PID) 
and its process channel, and it forms the link between the designated 
process and the requesting process. Processor connectors are described in 
greater detail in Invention No. 11 identified above. 
Resource/Connector Model 
The distributed system of the present invention may be viewed at several 
levels of complexity. The base level is the virtual machine, which defines 
and implements the device-independent architecture, consisting of virtual 
"instructions", i.e. the kernel primitives. 
Layered immediately above this, and closely related to it, is the 
process/message model which defines how programs are configured in the 
system and how they communicate with each other. 
Just above this level is a more abstract model dealing with "resources" and 
"connectors". As mentioned earlier, resources may be thought of as 
"logical devices". Resources are accessed through "connectors", which are 
essentially logical "pointers". 
An application must have a connector to a resource in order to interact 
with it. Connectors are granted and controlled by "resource manager 
processes", i.e. processes which can be requested to create, delete, etc. 
resources. 
Resource manager processes respond to connector messages to "create" new 
resources and "delete" old ones, and to "open" an existing resource (i.e. 
ask for a connection to it) and later to "close" it (terminate the 
connection to it). 
The response to creating a resource, or opening a connection to it, is a 
connect message. This message contains a service-independent connector 
data structure which uniquely identifies the resource. 
An application may create a new resource, or acquire access to an existing 
one, by making a request to the appropriate resource manager process. 
(Note that all resources remain controlled and protected by the resource 
manager process, and they are kept in its context.) As a result, a 
connector to the resource is returned to the application, allowing it to 
communicate directly with the resource. Note that in general two 
connectors are required one for the resource manager process, and one for 
the resource (although in many cases the resource manager process can be 
accessed by name). 
When a connector is received in a message, it identifies a specific 
resource to which the receiving process has access. The entire connector 
must be copied into subsequent request messages to the resource. The 
messages themselves are usually sent in "direct" mode, passing the address 
of the connector. As mentioned above, messages to the resource's manager 
can be sent by name, if appropriate, or via an explicit connector (to the 
manager), if available. 
Both "create" and "open" requests to the resource manager process usually 
expect a process name as a parameter, and both return a connection 
message. A "create" request without a name causes the service to generate 
a unique name An "open" request using a connector instead of a name may be 
employed to access the resource differently or to gain access to a closely 
related resource. The "delete" and "close" requests may accept either an 
explicit connector to the resource or the resource's name. 
There are five formats for connection messages: "create", which requests 
the creation of a new resource; "open", which establishes a connection to 
an existing resource; "delete", which requests that a specified resource 
be removed from the system; "close", which requests that the connection to 
a resource be terminated; and "connect", which provides a connection to a 
resource. The "connect" message normally represents a response to a 
"create" or "open" request and is not generally sent unsolicited. 
Data exchange messages are another type of message used in the distributed 
system of the present invention. Data in any format is sent solely by 
means of the "write" message. Data is requested by the "read" message (to 
which "write" or "failed" are the only responses. 
Process which only generate data should respond with "failed" to "write" 
requests. Conversely, a write-only resource should return "no data" (i.e. 
a "write" message without a data "triple") if it receives a "read" 
request. 
There are two formats for data exchange messages: "write", which is used to 
send data; and "read", which is used to request data. A "write" message 
includes the source of the data, the destination resource, the originator 
of the data, the type of data (if known), and it contains a block of data. 
A "read" message includes the destination resource, an optional prompt 
string (which must be written exactly before any data is read), and a 
protect parameter which indicates that the input should be protected if 
possible. 
Appropriate status messages are used to convey the completion status of a 
request, or the current state of a service or resource. In the latter 
case, the status message may be requested explicitly or may be sent as the 
result of a synchronous event within the resource itself. 
There are four formats for status messages: "query", which asks for the 
current status of a resource; "done", which indicates that a previous 
request has successfully completed; "failed", which indicates that a 
previous request has not completed; and "status", which gives the status 
of a resource, either in response to "query" or as the result of an 
asynchronous condition. 
DETAILED DESCRIPTION OF THE INVENTION 
FIG. 8 shows how Process Creation Monitor (PCM) messages and Process 
Termination Monitor (PTM) messages are sent between Process Manager 
Processes (PMP) in a distributed data processing system of the type 
incorporating the present invention. A process Creation Trap as used 
herein is a program, or routine, which is triggered by the creation of a 
process. The trap may suspend the process pending further action and will 
send a notification of the creation of the process via a message to the 
requesting process, or the like. Similarly, a Process Termination Trap as 
used herein is a program, or routine, which is triggered by the 
termination of a process. The trap may suspend the termination of the 
process pending further action and will send notification of the 
termination of the process via a message to the requesting process, or the 
like. A Process Manager Process exists at the most basic level of the 
operating system, i.e. the kernel. It is the only process which can create 
and terminate processes. There is exactly one Process Manager Process in 
every node of the system, such as nodes 152-154 shown in FIG. 8. 
Any process, such as process "y" on node 152, can send a Process Creation 
Monitor (PCM) request message or a Process Termination Monitor (PTM) 
request message to the Process Manager Process (PMP) residing on its own 
node. If the monitor request refers to processes to be created or 
terminated on other nodes, the PMP of the host node forwards or broadcasts 
the request to the PMP of another or all other nodes. 
The request for notification can be made specific to one node, several 
nodes, or the entire system. On the other hand, it may be limited to one 
context. The requesting process can be located anywhere in the system. 
A monitor request is not forwarded or broadcasted to any other node if the 
requesting process explicitly restricts the scope of the request to the 
local node; if it restricts the scope of the request to a context of 
processes local to the host node; or if the request explicitly identifies 
a process to be monitored that exists on the local node. For example, the 
PTM request "ml"0 to monitor process "x" existing on the same node is kept 
by the PMP of the host node 152. 
A monitor request is forwarded to another node if the requesting process 
explicitly restricts the scope of the request to that of another node; if 
it restricts the scope of the request to a context of processes local to 
that other node; or if the request explicitly identifies a process to be 
monitored that exists on that other node. For example, the PCM request 
"m2" to monitor creation of processes in the context of the "z" process 
existing on node 153 is forwarded to the PMP of that node, and it is not 
kept on the local node. 
A monitor request is broadcasted to all nodes if the requesting process 
does not restrict the scope of the request and it does not identify any 
specific existing process or if it restricts the scope of the request to a 
context of processes that spans all nodes of the network. A monitor 
request broadcasted to all nodes is also stored on the host node. For 
example, the PCT request "m3" to monitor creation of processes with the 
name of "foo" regardless of its location in the network is broadcasted to 
both nodes 153 and 154 in addition to keeping it on the node 152 as well. 
The Process Creation Monitor or Process Termination Trap request specifies 
that a receiving Process Manager Process notify the requesting process y 
whenever a designated process is created or terminated on nodes 152, 153, 
or 154. 
When a process is created with the name designated in the Process Creation 
Monitor, the Process Manager Process that received the Creation Monitor 
Request then replies to the process or processes which requested that the 
Process Creation Monitor be set, and the monitor is released. This is 
referred to as the "resolution" of a Process Creation Monitor. 
Likewise when a process is terminated which was identified in the Process 
Termination Monitor, the Process Manager Process responsible for 
terminating such process then replies to the process or processes which 
requested that the Process Termination Monitor be set, and the Monitor is 
released. This is referred to as the "resolution" of a Process Termination 
Monitor. 
FIG. 9 shows a distributed data processing system comprising network 171 
with nodes 172 and 176, each having a Process Manager Process (PMP). At 
node 172 user processes a and b both desire to be informed if and when a 
process x is created, so they send Process Creation Monitor request 
messages to the Process Manager Process on node 172. If process x is 
subsequently created, by whatever process in the system for whatever 
reason, the Process Manager Process on node 172 notifies both processes a 
and b of the fact. 
It is useful for user processes to know where to find various serving 
processes which have been created, e.g. a fast Fourier analysis process, 
Event Log Service Process (see FIG. 11), etc. 
With respect to other features of the invention, various other actions may 
be specified regarding the setting or resolution of Process Creation 
Monitors or Process Termination Monitors, or regarding monitored 
processes. For example, Process Creation Monitor requests may be made 
conditional upon the current existence of processes with the designated 
name. Also, process monitor requests may specify that resolved monitors 
are to be automatically reinstated. In this case a replied monitor is not 
released. 
In addition, a Process Creation Monitor request may specify that monitored 
processes are to be suspended until such suspension is released. Also the 
requesting process may request the removal of process monitors which have 
been unresolved within some period of time, or it may request such removal 
unconditionally. Further, the requesting process may request that 
information regarding the created/terminated process in addition to its 
name should be returned to the requesting process upon resolution of the 
process monitor. 
A Process Creation Monitor may or may not specify the name of the process 
whose creation has to be monitored. If the process name is not specified, 
any process created in the specified scope is monitored. 
If the scope of a Process Creation Monitor request is the entire network, 
such as network 151, then the Process Manager Process of the requesting 
node (e.g. node 152) broadcasts the monitor request to the Process Manager 
Processes of all nodes 152-154 of the network. When the Process Creation 
Monitor is resolved by the Process Manager Process of a node, and monitor 
removal upon resolution is requested, the trap resolution is reported to 
the Process Manager Processes of all nodes. A remotely resolved Process 
Creation Monitor is always replied through the Process Manager Process of 
the requesting node in order to eliminate race conditions which could 
occur in the case of simultaneous monitor resolutions. 
FIG. 10 shows a distributed data processing system illustrating how Process 
Manager Processes are notified when a Process Creation Monitor is resolved 
on a remote node. A network 181 comprises nodes 182, 185, 187, and 189, 
each having a Process Manager Process (PMP). Each node also has an 
associated list of monitors 183, 186. 188, and 190. Any time such node 
receives a PCM with a process name, it adds to its list of monitors the 
name of the process whose creation is to be reported. 
Assume that a process located at node 187 broadcasts a Process Creation 
Monitor request for a process x. Each of the nodes then adds process x to 
its associated list of monitors. Assume too that process x is subsequently 
created at node 182. Then the Process Manager Process at node 182 will 
delete process x from its list of monitors and add process x to its list 
of processes 184. The PMP of node 182 next notifies the PMP of node 187 
that process x was created. Then the PMP of node 187 notifies the other 
PMP's of the network (i.e. on nodes 185 and 189) that process x was 
created. 
If the process specified in a Process Termination Monitor cannot be located 
on the requesting node, the request is forwarded to the Process Manager 
Process of the next node. It is forwarded in the ring of Process Manager 
Processes until the process is found. A resolved Process Termination 
Monitor is always directly replied from the node of resolution to the 
process requesting the Process Termination Monitor regardless of its 
location in the network. 
The present invention has significant utility in several respects, 
particularly in the distributed, process/message system herein-disclosed. 
Numerous modules of the operating system rely upon notification of process 
creations and terminations--for example, configuration management, error 
management, debug services, performance monitors, process directory, and 
system statistics reporters. 
Process creation and termination monitor messages provide a facility to 
link to the Process Management from these modules at run-time. The process 
monitor messages also reduce the dependency of these modules on the 
process description representation details. 
In a conventional operating system, resources (e.g. files) allocated by 
processes are recorded in the process description data structures. The 
release of resources allocated by terminating processes have to be 
explicitly initiated by a process termination algorithm. Therefore, 
changes in the configuration of the system-wide supported resource types 
have to be reflected in the process description data structures and in the 
process termination algorithm. 
In the present invention, by requesting a Process Termination Monitor at 
each resource allocation for a process, the resource managers are notified 
when the allocating process terminates, and the resource release can be 
initiated by the resource manager itself. Adding new types of resource 
managers to the system does not change the process description data 
structure or the process termination algorithm. 
For example, if a process is terminated because of a fault or because it is 
completed, normally it is important to release all resources which have 
been allocated to such process. 
Also in a multiprocess system, various functions can be invoked upon the 
creation of a process. Process Creation Monitors provide a simple, 
efficient, and configurable way of passing control between functions and 
of synchronizing functions. 
FIG. 11 shows how the present invention may be used to facilitate error 
management in a distributed data processing system. In network 161 each 
node 162-164 may have one or more resources associated with it (not 
shown). For an Error Management Process (EMP) it is desirable to access an 
Event Log Service Process (ELSP) on any node for the purpose of logging 
various events associated with such nodal resources. When an ELSP is first 
created, for example on node 154, one or more error management processes 
in the network may be notified, so that such error management processes 
are made aware of the location of the ELSP in the system, so that the ELSP 
can be polled, given commands, etc. 
Otherwise, if no ELSP is accessible, the error management processes have to 
use lower level system services to log events in simpler form; these are 
available on every node. 
DESCRIPTION OF PROGRAM LISTINGS 
Program Listing A contains a "C" language implementation of the concepts 
relating to the process monitors as described hereinabove. These concepts 
are also represented in flowchart form by FIGS. 12A-12H for the 
convenience of the reader. 
FIG. 12A shows a flowchart illustrating an operation by a Process Manager 
Process (PMP) to Set a Process Creation Monitor. This operation is 
performed by appropriate code contained within Program Listing A of the 
present invention. In decision block 200 if the PMP is receiving its own 
broadcast the routine is terminated; but if not it proceeds to decision 
block 201. In decision block 201 if the monitor request is correct, the 
routine proceeds to block 203; if not, the routine passes to block 202 to 
generate a bad request notification. 
In decision block 203 the request is checked if it has a correct scope 
local to the node; if yes, a creation monitor data structure is allocated 
and initialized in block 204; otherwise the request is either forwarded to 
other nodes or it is rejected. 
In block 205 the new monitor data structure is inserted either in the list 
of unresolved creation monitors for a given process name that are 
organized in a hash table, or it is inserted in the list of unnamed 
process creation monitors that are linked according to the scope of the 
monitor. 
Next in decision block 206 if this is a conditional monitor, the routine 
passes to decision block 207; if not it proceeds to decision block 208. In 
decision block 207 if the process already exists the routine passes to 
block 212 where the creation monitor is resolved if not it proceeds to 
decision block 208. 
In decision block 213, if the resolved conditional monitor is to be held, 
the monitor may get broadcasted to other nodes; else the routine 
terminates. 
In decision block 208 if there is no node in the network the routine 
terminates; otherwise it proceeds to decision block 209. In decision block 
209 if the monitor was broadcasted from another node the routine 
terminates; otherwise it proceeds to decision block 210. In decision block 
210 if this monitor is not restricted to the local node, the routine 
passes to block 211, where the monitor is broadcasted to all PMP's in the 
network; otherwise the routine terminates. 
FIG. 12B shows a flowchart illustrating an operation to Set a Process 
Termination Monitor. In decision block 220, it checks whether a single 
process is monitored; if yes, it proceeds to check in block 221 whether 
this is a process existing on the local node. If not, in decision block 
222 it checks whether the request refers to a remote process; if yes, in 
block 223 the request is forwarded to the next node in the ring; else the 
routine terminates rejecting the request. 
If the local process exists, in block 224 the termination monitor data 
structure is created; then in block 225 it is linked to the Process 
Control Block of the specified process. 
If the request did not specify a single process, in decision block 226 the 
specification of a node or a group of processes is checked; if these are 
not specified either, the request is rejected in block 227. 
Otherwise, in decision block 228 the existence of the scope on the local 
node is checked, if it exists, the termination monitor is inserted in the 
list of scoped termination monitors for this node in block 229; else a 
remote target scope is searched starting from decision block 222 similarly 
to the single process termination monitor requests. 
FIG. 12C shows a flowchart illustrating an operation to Resolve a Process 
Termination Monitor. In decision block 230 if the monitor is not set for 
the terminating process, the routine terminates; otherwise it passes to 
block 231, where a reply is made to the monitor request message and the 
monitor is freed. After block 231 the routine passes to decision block 
232. In decision block 232 if no more monitors are set for the terminating 
process, the routine passes to block 233, where the monitor pointer is 
cleared in the Process Control Block; if not the routine returns to block 
231. 
After all possible termination monitors on this one specified process have 
been resolved, in block 234 a similar algorithm resolves all scoped 
monitors where the terminating process falls in the specified scope. 
FIG. 12D shows a flowchart illustrating an operation to Resolve a Process 
Creation Monitor. In decision block 240, if the created process is in the 
scope of the located monitor, it proceeds to block 241 to check if the 
monitor is to be held; otherwise it proceeds to block 245 to check whether 
there are more monitors to check for the same process name or scope. 
If the monitor should not be held, it is replied in block 242; else only a 
notification is sent to the requesting process in block 246. In both cases 
it is checked whether the monitor was conditional in blocks 243 and 247; 
if yes, the data structure of the resolved monitor is removed. 
If the monitor was not conditional and it did not have to be held, a 
creation monitor removal request is broadcasted to all nodes of the 
network in block 244. 
If no more monitors are set on the same process name and on an encompassing 
scope, the resolved data structures are removed in block 248; else the 
next monitor in the list is checked in decision block 240. 
FIG. 12E shows a flowchart illustrating an operation to handle a Creation 
Monitor Resolution From Other Nodes. In decision block 250 if the monitor 
list is found for the created process name, the routine passes to decision 
block 251; if not it proceeds to block 256, where the remote notification 
is freed. 
In decision block 251 if the monitor is locked, then the routine passes to 
block 256; if not it proceeds to decision block 252. In decision block 252 
if there is a monitor with a matching scope, the routine passes to block 
253; otherwise it proceeds to decision block 255. In block 253 a reply is 
made to the monitor request, and the routine then passes to block 254, 
where a request to remove the monitor is broadcast. After block 254 the 
routine passes to block 256. 
In decision block 255 if more monitors are set on the same process name, 
the routine returns to decision block 252; if not it proceeds to block 
256. 
FIG. 12F shows a flowchart illustrating an operation to Cancel a Process 
Creation Monitor. In decision block 260, if own broadcast is received, the 
routine terminates; else in decision block 261 it is checked if any scope 
is specified in the cancel request. If yes, it proceeds to decision block 
262 to check if the scope belongs to a remote node; else it proceeds to 
block 265. 
If a remote scope was specified, the request is forwarded to the next node 
in block 263; else in decision block 264 the correctness of the specified 
scope is checked: whether the scoping process exists and whether it is a 
context process. If the local scope is incorrect, the request is rejected 
and the routine terminates; else it proceeds to block 265. 
In block 265, a monitor that satisfies the specification of the cancel 
request is searched for, and in decision block 266 it is checked if such 
monitor was found; if not, it proceeds to block 272; else in decision 
block 267 it is checked if the located monitor contains a specific process 
name. If yes, in block 270 all monitors are removed from the hashed list 
of named process monitors that specify the same process name and a scope 
that encompasses the scope specified in the cancel request; if not, in 
block 271 all monitors are removed from the list of unnamed process 
monitors that specify an encompassing scope. 
If no monitors have been found on the node or when all matching monitors 
have been removed, the routine proceeds to decision block 272 to check 
whether the cancel request has to be broadcast. If yes, it proceeds to 
block 273 to broadcast the cancel request; else it directly proceeds to 
block 272 to reply to the cancel request if requested or to free the 
request message. 
FIG. 12G shows a flowchart illustrating an operation to Check If a Creation 
Monitor is Set. In decision block 280 a check is made to see whether the 
monitor counter is set to zero; if so the routine passes to block 281 to 
return a FALSE indication; if not it passes to block 282, where it finds 
the first monitor with a matching name hash and then proceeds to decision 
block 283. 
In decision block 283 if the name to check is the same as in the monitor 
and the created process is in the scope of the trap, the routine passes to 
block 284, where the monitor is locked and then to block 285 to return a 
TRUE indication; if not it passes to decision block 286. In decision block 
286 if there are more monitors with a matching name hash, the routine 
returns to decision block 283; if not it proceeds to block 287. 
In decision block 287 a similar algorithm is used to determine if there is 
any unnamed creation monitor set such that the new process is in the scope 
of the monitor; if yes, the routine proceeds to block 288 to return with a 
FALSE Boolean value, indicating that no creation monitor to resolve has 
been found. 
FIG. 12H shows a flowchart illustrating an operation to Cancel a Process 
Termination Monitor. In decision block 290 if a target process is 
specified, the routine passes to decision block 292; otherwise it passes 
to block 287, where it checks if a scope is specified in the monitor 
cancellation request. In decision block 292 if the process is expected on 
the same node, the routine passes to decision block 294; if not it passes 
to block 293, where the termination monitor is forwarded in the logical 
ring and terminated. 
In decision block 294 if the target process exists and the monitor is set, 
the routine passes to block 295, where all monitors set by the cancelling 
process are removed, and it passes then to block 296, where a reply is 
generated if it has been requested. In decision block 294 if the 
conditions are not true, then the routine passes to block 296 and 
terminates. 
In decision block 297, if no cancellation scope is specified either, the 
request message is rejected as a bad request in block 291; else it 
proceeds to block 298, where all relevant scoped termination monitors are 
cancelled using a similar algorithm and the routine exits. 
______________________________________ 
Correlation of Flowcharts to Program Listing 
Line Numbers in 
Program 
Listing A 
______________________________________ 
Set Process Creation Monitor 
Own broadcast received 73 
Check if correct request 
76-82 
Check if correct local scope 
91-101 
Create monitor data structure 
108-138, 184-185 
Insert monitor in named creation trap list 
139-161 
Insert monitor in scoped creation trap list 
162-181 
Conditional monitor 191 
Process exists already 192 
Resolve creation monitor 
193 
Monitor to hold 194 
Node in network 202 
Monitor was broadcasted from another node 
203 
Monitor for whole network 
202, 203 
Broadcast monitor to all Process Management 
204-208 
Processes 
Set Process Termination Monitor 
Check if single target process specified 
236 
Check if local process exists 
239 
Check if remote process 241, 271 
Forward request in ring 264, 272 
Create termination monitor 
243-251 
Link monitor in the target Process Control 
253-260 
Block 
Check if node or group of processes specified 
267, 281 
Reject request message 285 
Check if local scope exists 
268, 270 
Insert monitor in scoped termination trap list 
269, 282, 290-330 
Resolve Process Termination Monitor 
Monitor set for terminating process 
968 
Reply to monitor request message and free 
972-978 
trap 
More monitors set for terminating process 
970, 971, 979 
Clear pointer in the Process Control Block 
981 
Resolve scoped termination monitors 
984, 1006 
Resolve Process Creation Monitor 
Check if monitor in specified scope 
564 
Check if monitor to hold 
576 
Reply to monitor request 
577-586 
Check if monitor was conditional 
571-574, 587 
Broadcast creation monitor removal 
590, 613-623 
More monitors set on same name or scope 
562, 565, 601, 602 
Send notification 593-596 
Check if monitor was conditional 
597 
Remove resolved monitor data structures 
604, 605, 685-842 
Creation Monitor Resolution from other 
Nodes 
Monitor list for created process name found 
864, 894-914 
Monitor is locked (being resolved on the 
864 
monitor 
setting node) 
Monitor with matching scope 
866-867 
Reply to monitor request 
868-873 
Broadcast request to remove the monitor 
874, 613-623 
More monitors set on same process name 
865, 878-879 
Free remote notification and the resolved 
881-885 
monitors 
Cancel Process Creation Monitor 
Own broadcast received 365 
Scope of cancel specified 
375 
Remote scope 377, 378 
Forward request in logical ring 
379 
Correct local scope specified 
377, 383 
Search for specified monitor(s) 
399, 441 
Monitor found 441 
Monitor on named process 
444 
Remove matching named monitors 
445, 446 
Remove matching unnamed monitors 
448 
Cancel from same node and scope not local 
401 
Broadcast cancel request 
402, 404 
Reply if requested from same node and free 
407-424 
request 
Check if Creation Monitor Set 
Monitor counter zero 643 
Find first monitor with matching name hash 
646-648 
Name and scope match 655-656 
Lock monitor (to allow nonresident monitored 
660, 672 
process creation) 
More monitors with matching name hash 
654, 657, 658 
Cancel Process Termination Monitors 
Target process specified 
475 
Process expected on the same node 
477-480 
Target process exists and monitor set 
478, 485 
Remove all monitors set by cancelling process 
485, 1008-1069 
Reply if requested 486-495 
Forward termination monitor in ring 
481 
Scope specified 499 
______________________________________ 
It will be apparent to those skilled in the art that the herein disclosed 
invention may be modified in numerous ways and may assume many embodiments 
other than the preferred form specifically set out and described above. 
For example, the invention may be implemented on other types of data 
processing systems. It may also be used to provide additional attributes 
regarding created and/or terminated processes, such as whether the process 
is a context process. Also, it may be used for providing notification of 
other types of events. 
Accordingly, it is intended by the appended claims to cover all 
modifications of the invention which fall within the true spirit and scope 
of the invention.