Abstract:
A method for communication between first and second computer programs having a shared memory. The first computer program has a first work dispatcher for a first work queue. The second computer program has a second work dispatcher for a second work queue. Without causing an interrupt, a message or data is written for the second program from the first program to the shared memory and the second work queue is updated with a work item indicating a message or data for the second program. In association with the updating step, it is determined if the second program is currently busy. If so, the second program is not interrupted regarding the message or data. When the second program subsequently becomes not busy, the second program receives, without an interrupt, and executes the work item to receive the message or data. If the second program was not currently busy, the second program is interrupted to process the message or data on its work queue. This imposes a minimal burden on the second program.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The invention relates generally to computer systems and deals more particularly with an efficient technique for transferring messages and data between virtual machines, logical partitions or application programs.  
         [0002]     There are many computer environments in which two or more computer entities need to exchange messages or data. Such computer entities include virtual machines, logical partitions and applications running on a unitary operating system such as Unix or Windows NT.  
         [0003]     A virtual machine operating system is well known today and comprises a common base portion and separate user portions. In an IBM z/VM operating system, the common base portion is called the “Control Program” or “CP” and each user portion is called a “virtual machine” or “guest”. Many applications can run on each virtual machine. Each virtual machine has its own work dispatcher (and associated work queue) and appears to the user and his or her applications as a personal operating system. Each virtual machine executes commands on behalf of the applications they support. The different virtual machines can communicate with each other through the common base portion. The communications between the different virtual machines via CP may be in the form of messages conveyed by virtualized communication devices such as Guest Lan or IBM proprietary protocols such as IUCV. Though these communications are conveyed by a variety of protocols, all of these communication mechanisms have at least four common properties: 
        a) Message data is first written into the sender&#39;s virtual address space.     b) An interrupt is generated for each message in each of the receivers&#39; virtual machines.     This invokes interrupt handling in each receiver virtual machine.     c) CP must be invoked in order to accomplish the communication.     d) CP copies message data from the sender&#39;s virtual address space to all of the receivers&#39; virtual address spaces. 
 
 With the foregoing communication methods there is significant overhead associated with invoking CP, generating interrupts, processing interrupts, and copying the message data from the sender&#39;s virtual address space to the virtual address space of each of the receivers. 
       
 
         [0009]     The following is a more detailed description of IUCV. IUCV is an IBM proprietary point-to-point protocol. A point-to-point protocol transfers data from one sender to one receiver. To communicate via IUCV, a sender first invokes CP indicating the identity of the intended receiver of communication. CP generates an interrupt to the receiver and if the receiver agrees to communicate, CP provides the receiver with a communication path id. CP also then interrupts the sender and provides the sender with the communication path id. To send data, the sender invokes CP indicating the previously obtained path id and the data to be sent. CP uses the path id to identify the receiver and generates an interrupt to the receiver. The receiver responds to the interrupt by invoking CP to receive the data. CP then copies the data from the sender&#39;s virtual address space to the receiver&#39;s virtual address space and generates an interrupt to the sender indicating that the data has been transferred.  
         [0010]     The following is a more detailed description of Guest Lan. Guest Lan is a virtualized communication device using local area network (LAN) protocol. Lan protocol allows communication between a sender and multiple receivers simultaneously. To communicate via a Guest Lan, both sender and receivers invoke CP indicating that they wish to participate in the Guest Lan. To send data, the sender invokes CP indicating the data to be sent and which receivers should get the data. CP generates an interrupt for each identified receiver. The receivers each respond by invoking CP to receive the data. CP then copies the data from the sender&#39;s virtual address space to the virtual address spaces of each of the receivers. Once all receivers have received the data, CP generates an interrupt to the sender indicating that the data has been transferred to all receivers.  
         [0011]     A logical partition environment is also well known today. A logical partition is a logical division of resources of a single computer system, which division is accomplished by software and microcode. Each logical partition is defined by a respective configuration of CPU(s), memory and peripheral devices. An operating system running in a logical partition views its logical partition as nearly indistinguishable from a real computer, although the logical partition may provide some additional services not available on a real machine. Therefore, the operating system is largely unaware that it is running in a logical partition, and is largely unaware of other logical partitions of the same real computer. Each logical partition also has its own dispatcher, and uses interrupts to communicate messages/data from one logical partition to another as in the virtual machine environment.  
         [0012]     There are other known techniques for one application to communicate with another application when both applications are running on the same operating system, such as Windows NT or Unix. In this environment, the operating system utilizes the same dispatcher for both applications. According to these known communication techniques, when application “A” wants to communicate with application “B”, application A calls/notifies the supervisor within the operating system. The call includes the address of the message/data in memory accessible by application A. In response, the supervisor copies the message/data to a location that application B can access. Next, the supervisor puts a work element on the dispatch queue. The work element identifies application B as the recipient, and includes a command to fetch the message/data. Then, the dispatcher dispatches the work element to application B at a time consistent with the dispatching strategy of the operating system and the relative priorities of the work elements. The following are some of the possible, known dispatching strategies. If application B is not currently busy, then the message/data work element is dispatched to application B when the processor becomes free and/or is not occupied with processing higher priority work elements (for any application). If application B is currently busy with another, lower priority work item, then the dispatcher may substitute the message/data work item when the lower priority work item completes its allotted processor time slice or makes a call to the operating system. But, it would not be appropriate to “interrupt” the operating system to convey the message/data to application B because of the overhead involved. The sharing of the dispatcher makes this unnecessary. As noted above, virtual machine, logical partition and other environments do not have a common dispatcher.  
         [0013]     An object of the present invention is to provide an efficient method for communication/data transfer between (a) two different virtual machines running on the same base operating system, (b) two logical partitions of the same computer or (c) two applications running on the same computer but having different dispatchers.  
         [0014]     An object of the present invention is to provide an efficient method for communication/data transfer from (a) one virtual machine to two or more other virtual machines all running on the same base operating system, (b) from one logical partition to two or more other logical partitions of the same computer or (c) one application to two or more other applications running on the same computer but having different dispatchers.  
       SUMMARY OF THE INVENTION  
       [0015]     The invention resides in a method for communication between first and second computer programs having a shared memory. The first computer program has a first work dispatcher for a first work queue. The second computer program has a second work dispatcher for a second work queue. A message or data is written for the second program from the first program to the shared memory and the second work queue is updated with a work item indicating a message or data for the second program. In association with the updating step, it is determined if the second program is currently busy. If so, the second program is not interrupted regarding the message or data. When the second program subsequently becomes not busy, the second program receives, without an interrupt, and executes the work item to receive the message or data. If the second program was not currently busy, the second program is interrupted to process the message or data on its work queue. (This imposes a minimal burden on the second program.)  
         [0016]     According to another feature of the present invention, there is a method for communication between first and second virtual machines having a shared memory and a common base operating system. The first virtual machine has a first work dispatcher for a first work queue. The second virtual machine has a second work dispatcher for a second work queue. The first and second work queues reside in memory shared by both the first and second virtual machines. Without invoking the common base operating system, a message or data is written for the second virtual machine from the first virtual machine to the shared memory and the second work queue is updated with a work item indicating a message or data for the second virtual machine. Subsequently, the second virtual machine program reads the message or data from the shared memory. 
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0017]      FIG. 1  is a block diagram of a virtual machine operating system according to the present invention.  
         [0018]      FIG. 2  is a flow chart illustrating a process implemented by a virtual machine of  FIG. 1  to receive a message or data from another virtual machine, according to the present invention.  
         [0019]      FIG. 3  is a flow chart illustrating a process implemented by a virtual machine of  FIG. 1  to send a message or data to another virtual machine, according to the present invention.  
         [0020]      FIG. 4  is a block diagram of a logically partitioned computer system according to the present invention.  
         [0021]      FIG. 5  is a flow chart illustrating a process implemented by a logical partition of the computer system of  FIG. 4  to receive a message or data from another logical partition, according to the present invention.  
         [0022]      FIG. 6  is a flow chart illustrating a process implemented by a logical partition of  FIG. 5  to send a message or data to another logical partition, according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]     Referring now to the figures in detail, wherein like reference numbers indicate like elements throughout,  FIG. 1  illustrates a virtual machine operating system generally designated  10  according to the present invention. By way of example, virtual machine operating system  10  can be IBM z/VM version 4.2.0 or 4.3.0 operating system although the present invention can be incorporated into other virtual machine and non virtual machine operating systems as well. The details of the z/VM 4.2.0 operating system are disclosed in IBM publication “z/VM 4.2.0 General Information” (Document Number: GC24-5991-03) which is available from International Business Machines Corp. at PO Box 29570, IBM Publications, Raleigh, N.C. 27626-0570 or on the WWW at www.IBM.com/shop/publications/order. This publication is hereby incorporated by reference as part of the present disclosure. Operating system  10  executes in a physical computer  11  such as an IBM zSeries mainframe although the present invention can be implemented in other server computers or personal computers as well. Operating system  10  comprises user portions  12 ,  14 ,  16  . . . (called “virtual machines” or “guest virtual machines” in the z/VM operating system) and common base portion  20  (called “CP” in the z/VM operating system). Each user portion  12  and  14  provides standard operating system functions such as I/O, communication, etc. Each user portion  12 ,  14  and  16  is capable of concurrently executing a number of different applications such as applications  32 ,  34  and  36  as shown. By way of examples, applications  32 ,  34  and  36  can be TELNET, FTP and PING (and use the present invention instead of the prior art communication mechanisms). In the z/VM 4.2.0 and 4.3.0 operating systems, the Linux™ (of Linus Torvalds) operating system can also run on each virtual machine  12 ,  14  and  16 , although some of the operating system functions of virtual machines  12 ,  14  or  16  are not needed by the Linux operating system as they are currently provided by the Linux operating system. Although not shown, typically there are many other virtual machines and associated operating systems which also share common base portion  20 . Also, there can be multiple applications executing on each virtual machine. Base portion  20  includes known functions such as virtualized memory, virtualized devices, and virtualized CPUs.  
         [0024]     Computer  11  also includes memory area  21  which is shared by all of the virtual machines  12 ,  14 ,  16  etc. Being “shared” each virtual machine can directly address and access the shared memory area  21  to read data therefrom or write data thereto. For data requested by an application or generated by an application, the application makes the read or write request to the respective virtual machine on which it is running. This respective virtual machines accesses the shared memory on behalf of the application as explained below with reference to  FIGS. 2 and 3 . In one (of many) embodiments of the present invention, the shared memory  21  is part of a Discontiguous Saved Segment (“DCSS”) portion of the base portion  20 . DCSS is a special form of shared memory that can be dynamically loaded and unloaded. It can survive virtual machine termination and even CP termination, and can contain executable code. However, functions other than shared memory within DCSS are not needed for the present invention, so the present invention is not limited to implementations involving DCSS or its equivalents.  
         [0025]     Each virtual machine  12 ,  14 , and  16  includes a respective read function  42   a,    42   b,  and  42   c,  a respective write function  33   a,    33   b  and  33   c  and a respective dispatcher  22   a,    22   b  and  22   c . The virtual machine calls the write function when it encounters a write command in the application it is executing. The write function is standing by, so no queue is required for the write function tasks. The write function writes data from a virtual machine to the shared memory. A write operation does not invoke CP. The virtual machine calls the read function when it encounters a read command in the application it is executing. The read function is standing by, so no queue is required for the read function tasks. The read function reads data from the shared memory. Thus, the data is not copied from the writer&#39;s virtual address space to the reader&#39;s virtual address space. Also, CP is not invoked to read from shared memory, and this reduces overhead. Each virtual machine calls/invokes its dispatcher when it completes a work item and therefore, needs another work item, if any. In response to the call, the dispatcher checks for work items on its respective queue  26   a,    26   b  or  26   c  within shared memory  21 .  
         [0026]     A table  24  is also stored in shared memory  21 . The table indicates the status of each virtual machine  12 ,  14 ,  16 . Each virtual machine  12 ,  14  and  16  also includes a respective Work Queue Management Function (“WQMF”)  81   a,    81   b  or  81   c  which adds work items to work queues when they arise and updates the status of each virtual machine as “idle” or “not idle” as described below. Table  24  includes an identity of each virtual machine and an indication whether or not the respective virtual machine is idle. Table  24  also includes for each virtual machine, a pointer to the respective work queue  26   a,    26   b  or  26   c.  Table  24  changes as the status changes. In the example illustrated in  FIG. 1 , currently virtual machine  12  is not idle, i.e. it is currently executing another work item/task. However, virtual machine  12  currently has nothing in its work queue  26   a  to do after completing its current work item. Virtual machine  14  is currently idle, but has a work item in its queue  26   b.  The work item in queue  26   b  is to read the contents of the shared memory beginning at location  24 D 00  and extending for the specified length. (The word “null” following the work item indicates that there are no further work items in the queue.) Virtual machine  16  currently is not idle, and has a work item in its queue  26   c.  The work item in queue  26   c  is to read the contents of the shared memory beginning at location  24 D 00  and extending for the specified length.  
         [0027]      FIG. 2  is a flow chart illustrating operation of each of the dispatchers, i.e. each of the dispatchers implements the steps of  FIG. 2  separately from the other dispatchers. After a virtual machine completes each work item/task it invokes its dispatcher to look for a new work item to perform (decision  48 ). In response, the dispatcher within the virtual machine checks the respective work queue (work queue  26   a  for dispatcher  22   a,  work queue  26   b  for dispatcher  22   b  and work queue  26   c  for dispatcher  26   c ) for a work item (step  50 ). If there is a work item in the queue (decision  52 ), then the dispatcher parses the work item to determine its nature and what function to call to perform the work item. In the case of a read request, the dispatcher calls the read function to read the message/data at the location indicated by the work item. Thus, this read can be accomplished without the generation of an interrupt and without invoking interrupt handling. Then, the dispatcher loops back to decision  52  to check the work queue again. If during any iteration of decision  52 , there is no work item in the work queue, then the dispatcher sets the status field in the table  24  as “idle” for the respective virtual machine (step  60 ). Then, the dispatcher notifies the virtual machine to enter into a wait state (step  62 ). In this wait state, the virtual machine is in a “sleeping” or “idle” mode where it is not executing any work items for an application or itself. The virtual machine will remain in this wait state until receiving an interrupt indicative of a new work item in its work queue (decision  66 ). When such an interrupt is received, the WQMF for the virtual machine sets the status field in the table  14  as “non idle” for the respective virtual machine (step  68 ). Next, the dispatcher loops back to decision  52  to check the work queue for a work item. At this time, there should be a work item in the work queue.  
         [0028]      FIG. 3  illustrates operation of one of the virtual machines, for example virtual machine  12  when it desires to send a message/data to another of the virtual machines, for example virtual machine  14 . In step  80 , virtual machine  12  calls its write function  33   a  to write data to the shared memory  21 . As explained above, each of the virtual machines has direct access to the shared memory by providing the appropriate address. So, the write function  33   a  of virtual machine  12  writes the data to the shared memory by specifying the address to be written and furnishing the data to be written. Next, Work Queue Management function (“WQMF”)  81   a  within virtual machine  12  adds a work item to the work queue  26   b  of virtual machine  14 , by writing the work item onto the work queue (step  82 ). Because the work queue is in shared memory, this does not require invocation of CP. Next, WQMF  81   a  determines if virtual machine  14  is currently idle by checking the table  24  (decision  84 ). If not, then virtual machine  12  does nothing further to complete this communication and CP is not invoked at any point in the communication process (termination step  86 ). In accordance with the present invention, virtual machine  12  does not interrupt virtual machine  14  because of the overhead involved in interrupting the virtual machine. As explained above with reference to  FIG. 2 , when virtual machine  14  completes its current work item, it will automatically invoke/call its dispatcher to check its work queue for another work item (decision  48  and step  50 ). At that time it will see the work item from virtual machine  12 . Referring again to decision  84 , if virtual machine  14  is idle, then in accordance with the present invention, virtual machine  12  issues a “wakening” type of interrupt to virtual machine  14  (step  88 ). This requires invocation of CP. The wakening type of interrupt alerts/invokes virtual machine  14  that there is a work item in its queue  26   b.  With the issuance of this interrupt, virtual machine  12  has completed its part of the data communication. The “wakening” interrupt automatically causes virtual machine  14  to activate its dispatcher  22   b  (decision  48  of  FIG. 2 ) to check its work queue for a work item. Dispatcher  22   b  then implements the steps illustrated in  FIG. 2  to check its work queue  26   b  (step  50  and decision  52 ) and then read the data with read function  42 ( b ) (step  54 ).  
         [0029]      FIG. 3  also illustrates operation of one of the virtual machines, for example virtual machine  12  when it desires to communicate with two or more other virtual machines, for example virtual machines  14  and  16 . In step  80 , virtual machine  12  calls its write function  32   a  to write data to the shared memory  21 . So, virtual machine  12  writes the data to the shared memory by specifying the address to be written and furnishing the data to be written. In the example illustrated in  FIG. 1 , the data was written to shared memory locations beginning at address  24 D 00 . Next, WQMF  81   a  within virtual machine  12  adds a work item to the work queues  26   b  and  26   c  of virtual machines  14  and  16 , by writing the work item, data address and data length onto the work queues (step  82 ). Next, WQMF  81   a  within virtual machine  12  determines if virtual machines  14  and  16  are currently idle by checking the table  24  (decision  84 ). In the example illustrated in  FIG. 1 , virtual machine  14  is idle but virtual machine  16  is busy. So, for virtual machine  16  which is busy, virtual machine  12  does nothing further to complete the communication (termination step  86 ). In accordance with the present invention, virtual machine  12  does not interrupt the busy virtual machine  16  because of the overhead involved in interrupting a virtual machine. As explained above with reference to  FIG. 2 , when the busy virtual machine  16  completes its current work item, it will automatically check its work queue for another work item (decision  48  and step  50 ). At that time it will see the work item from virtual machine  12  and the communication will be completed without invocation of CP. Referring again to decision  84 , because virtual machine  14  is idle, then in accordance with the present invention, virtual machine  12  issues a “wakening” type of interrupt to the idle virtual machine  14  (step  88 ). The wakening type of interrupt alerts/invokes the idle virtual machine  14  that there is a work item in its queue. With the issuance of this interrupt, virtual machine  12  has completed its part of the data communication. The “wakening” interrupt automatically causes the idle virtual machine  14  to invoke/call its dispatcher  22   b  to check its work queue for a work item. Dispatcher  22   b  then implements the steps illustrated in  FIG. 2  to check its work queue  26   b  (decision  52 ) and then read the data (step  54 ).  
         [0030]      FIG. 4  illustrates a logically partitioned computer system generally designated  110  according to the present invention. System  10  is a logical partition of a physical computer  11  such as an IBM zSeries mainframe although the present invention can be implemented in other server computers or personal computers as well. System  110  comprises logical partitions  112 ,  114 ,  116 . Each logical partition  112 ,  114  and  116  provides standard operating system functions such as I/O, communication, etc. to its applications. Each logical partition  112 ,  114  and  116  is capable of concurrently executing a number of different applications such as applications  132 ,  134  and  136  as shown. By way of examples, applications  132 ,  134  and  136  can be Telnet, FTP and Ping (and use the present invention instead of the prior art communication mechanisms). Base portion  120  participates in the actual logical partitioning of the computer  111  and its resources, i.e. partitions the CPU(s), partitions memory, partitions I/O, etc. The functions of one example of base portion  120  and logical partitions  112 ,  114  and  116 , aside from the present invention, are described in a document entitled “Enterprise System/9000 9221 Processors: Operating Your System—Volume 2 (Logically Partitioned Mode)”, Publication # SA24-4351-02, which document is available International Business Machines at PO Box 29570, B3M Publications, Raleigh, N.C. 27626-0570 or on the WWW at www.IBM.com/shop/publications/order.  
         [0031]     Computer  111  also includes memory area  121  which is shared by all of the logical partitions  112 ,  114 ,  116  etc. Being “shared” each logical partition can directly address and access the shared memory area  121  to read data therefrom or write data thereto. For data requested by an application or generated by an application, the application makes the read or write request to the respective logical partition on which it is running. This respective logical partition accesses the shared memory on behalf of the application as explained below with reference to  FIGS. 5 and 6 .  
         [0032]     Each logical partition  112 ,  114 , and  116  includes a respective read function  142   a,    142   b , and  142   c,  a respective write function  133   a,    133   b  and  133   c  and a respective dispatcher  122   a ,  122   b  and  122   c.  The logical partition calls the write function when it encounters a write command in the application it is executing. The write function is standing by, so no queue is required for the write function tasks. The write function writes data from a logical partition to the shared memory, and therefore does not invoke base portion  120 . The logical partition calls the read function when it encounters a read command in the application it is executing. The read function is standing by, so no queue is required for the read function tasks. The read function reads data from the shared memory, and therefore does not invoke base portion  120 . Also, the data is not copied from the writer&#39;s virtual address space to the reader&#39;s virtual address space. Each logical partition calls/invokes its dispatcher when it completes a work item and therefore, needs another work item, if any. In response to the call, the dispatcher checks for work items on its respective queue  126   a,    126   b  or  126   c  within shared memory  121 .  
         [0033]     A table  124  is also stored in shared memory  121 . The table indicates the status of each logical partition  112 ,  114 ,  116 . Each logical partition  112 ,  114  and  116  also includes a respective WQMF  181   a,    181   b  or  181   c  which adds work items to work queues when they arise and updates the status of each logical partition as “idle” or “not idle” as described below. Table  124  includes an identity of each logical partition and an indication whether or not the respective logical partition is idle. Table  124  also includes for each logical partition, a pointer to the respective work queue  126   a,    126   b  or  126   c.  Table  124  changes as the status changes. In the example illustrated in  FIG. 4 , currently logical partition  112  is not idle, i.e. it is currently executing another work item/task. However, logical partition  112  currently has nothing in its work queue  126   a  to do after completing its current work item. Logical partition  114  is currently idle, but has a work item in its queue  126   b.  The work item in queue  126   b  is to read the contents of the shared memory beginning at location  24 D 00  and extending for the specified length. (The word “null” following the work item indicates that there are no further work items in the queue.) Logical partition  116  currently is not idle, and has a work item in its queue  126   c.  The work item in queue  126   c  is to read the contents of the shared memory beginning at location  24 D 00  and extending for the specified length.  
         [0034]      FIG. 5  is a flow chart illustrating operation of each of the dispatchers, i.e. each of the dispatchers implements the steps of  FIG. 5  separately from the other dispatchers. After a logical partition completes each work item/task it invokes its dispatcher to look for a new work item to perform (decision  148 ). In response, the dispatcher within the logical partition checks the respective work queue (work queue  126   a  for dispatcher  122   a,  work queue  126   b  for dispatcher  122   b  and work queue  126   c  for dispatcher  126   c ) for a work item (step  150 ). If there is a work item in the queue (decision  152 ), then the dispatcher parses the work item to determine its nature and what function to call to perform the work item. In the case of a read request, the dispatcher calls the read function to read the message/data at the location indicated by the work item. Thus, this read can be accomplished without the generation of an interrupt and without invoking interrupt handling. Then, the dispatcher loops back to decision  152  to check the work queue again. If during any iteration of decision  152 , there is no work item in the work queue, then the dispatcher sets the status field in the table  124  as “idle” for the respective logical partition (step  160 ). Then, the dispatcher notifies the logical partition to enter into a wait state (step  162 ). In this wait state, the logical partition is in a “sleeping” or “idle” mode where it is not executing any work items for an application or itself. The logical partition will remain in this wait state until receiving an interrupt indicative of a new work item in its work queue (decision  166 ). When such an interrupt is received, the WQMF for the logical partition sets the status field in the table  114  as “non idle” for the respective logical partition (step  168 ). Next, the dispatcher loops back to decision  152  to check the work queue for a work item. At this time, there should be a work item in the work queue.  
         [0035]      FIG. 6  illustrates operation of one of the logical partitions, for example logical partition  112  when it desires to send a message/data to another of the logical partition, for example logical partition  114 . In step  180 , logical partition  112  calls its write function  133   a  to write data to the shared memory  121 . As explained above, each of the logical partitions has direct access to the shared memory by providing the appropriate address. So, the write function  133   a  of logical partition  112  writes the data to the shared memory by specifying the address to be written and furnishing the data to be written. Next, WQMF  181   a  within logical partition  112  adds a work item to the work queue  126   b  of logical partition  114 , by writing the work item onto the work queue (step  182 ). Next, WQMF  181   a  determines if logical partition  114  is currently idle by checking the table  124  (decision  184 ). If not, then the logical partition does nothing further to complete this communication and the base portion  120  is not invoked at any point in the communication process (termination step  186 ). In accordance with the present invention, logical partition  112  does not interrupt logical partition  114  because of the overhead involved in interrupting the logical partition. As explained above with reference to  FIG. 5 , when logical partition  114  completes its current work item, it will automatically invoke/call its dispatcher to check its work queue for another work item (decision  148  and step  150 ). At that time it will see the work item from logical partition  112 . Referring again to decision  184 , if logical partition  114  is idle, then in accordance with the present invention, logical partition  112  issues a “wakening” type of interrupt to logical partition  114  (step  188 ). The wakening type of interrupt alerts/invokes logical partition  114  that there is a work item in its queue  126   b.  With the issuance of this interrupt, logical partition  112  has completed its part of the data communication. The “wakening” interrupt automatically causes logical partition  114  to activate its dispatcher  122   b  (decision  148  of  FIG. 5 ) to check its work queue for a work item. Dispatcher  122   b  then implements the steps illustrated in  FIG. 5  to check its work queue  126   b  (step  150  and decision  152 ) and then read the data with read function  142 ( b ) (step  154 ).  
         [0036]      FIG. 6  also illustrates operation of one of the logical partitions, for example logical partition  112  when it desires to communicate with two or more other logical partitions, for example logical partitions  114  and  116 . In step  80 , logical partition  112  calls its write function  132   a  to write data to the shared memory  121 . So, logical partition  112  writes the data to the shared memory by specifying the address to be written and furnishing the data to be written. In the example illustrated in  FIG. 4 , the data was written to shared memory locations beginning at address  24 D 00 . Next, WQMF  81   a  within logical partition  112  adds a work item to the work queues  126   b  and  126   c  of logical partitions  114  and  116 , by writing the work item, data address and data length onto the work queues (step  182 ). Next, WQMF  181   a  within logical partition  112  determines if logical partitions  114  and  116  are currently idle by checking the table  124  (decision  184 ). In the example illustrated in  FIG. 4 , logical partition  114  is idle but logical partition  116  is busy. So, for logical partition  116  which is busy, logical partition  112  does nothing further to complete the communication (termination step  186 ). In accordance with the present invention, logical partition  112  does not interrupt the busy logical partition  116  because of the overhead involved in interrupting a logical partition. As explained above with reference to  FIG. 5 , when the busy logical partition  116  completes its current work item, it will automatically check its work queue for another work item (decision  148  and step  150 ). At that time it will see the work item from logical partition  112  and the communication will be completed without invocation of base portion  120 . Referring again to decision  184 , because logical partition  114  is idle, then in accordance with the present invention, logical partition  112  issues a “wakening” type of interrupt to the idle logical partition  114  (step  188 ). The wakening type of interrupt alerts/invokes the idle logical partition  114  that there is a work item in its queue. With the issuance of this interrupt, logical partition  112  has completed its part of the data communication. The “wakening” interrupt automatically causes the idle logical partition  114  to invoke/call its dispatcher  122   b  to check its work queue for a work item. Dispatcher  122   b  then implements the steps illustrated in  FIG. 5  to check its work queue  126   b  (decision  152 ) and then read the data (step  154 ).