Abstract:
A method, suitable for use in client/server system, which allows multiple copies of a single-user application to run simultaneously in a multi-user operating system without modification of the single-user program, by modifying existing operating system methods used for object name creation, look-up, and deletion. The method creates a user global context by labeling each instance of the single-user application with a user identifier (name) that defines a single-user name space in which each labeled object is only available to the named user. In addition, the single-user server process is allowed to impersonate the client for allowing the server to access the named resources of the single-user name space. A coexisting system global context is also created by marking system global named resources.

Description:
FIELD OF INVENTION 
     The invention relates to multi-user distributed process systems having a master process and a plurality of service processes and a method for adapting applications written for a single user environment for use in the multi-user system without recompiling. 
     BACKGROUND TO THE INVENTION 
     The distributed process system described is a multi-user and multi-tasking system. Applications written for a multi-user environment typically assume that more than one copy of the application may be active at the same time. Multi-tasking operating systems (Windows NT and Unix for example) provide the capability to create various types of shared objects for providing interprocess communications and synchronization. By associating a name with an object, it allows for one process to create an object and for another process to make use of it. Synchronization ensures that only one process has control of a resource at a time. Resources include objects such as global variables, common data memory, file handles, and shared object handles. 
     Shared objects used for synchronization and interprocess communication include: 
     Semaphores and event objects for coordinating threads; 
     Mutexes, a mutually exclusive semaphore allowing a single thread access at a time; 
     Named Pipes for duplexed interprocess and interprocessor connection; 
     Message Queues for one way, many to one communications; and 
     Shared Memory for use by all processes that have authorized access. 
     If an application was written for a single user for running under a single user operating system, such as Windows NT (produced by Microsoft Corp. of Redmond, Wash.), and then is run in a multi-user environment under a compatible multi-user operating system, such as WinFrame™ (produced by Citrix Systems, Inc. of Coral Springs, Fla.), in a multi-user environment, it is possible for name collisions to occur if more than one copy of the same application is executed at the same time. The application would have to be modified and recompiled in order for it to execute reliably in the multi-user environment. 
     The present invention modifies the existing methods used for object name creation, look-up, and deletion in a multi-user operating system so that multiple copies of a single user application are able to run simultaneously. 
     SUMMARY OF THE INVENTION 
     A method is described for allowing a single-user application program to operate in a multi-user operating system without modification of the single-user program by modifying existing operating system methods used for object name creation, look-up, and deletion, so that multiple copies of a single-user application program are able to run simultaneously. 
     The method includes the following steps: 
     a) assigning a unique identifier to each user on the system and each of the user&#39;s applications, and attaching this same identifier to each instance of an object created by the user&#39;s applications, for the purpose of creating a distinct single user name space that is only accessible by the same single user; and 
     b) enabling a server process that is serving the application of the single user process to impersonate the single user process by assuming the identity of the single user process, for allowing the server process to access the single user name space. 
     In this manner, the server process assumes the role of the user, has access to the user&#39;s private name space and to all objects required for serving the user&#39;s application. The combination of user labeling and user impersonation allows multiple copies of a given application to run simultaneously even though the application was written for a single-user operating system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention may be more fully understood from the detailed description given below and from the accompanying drawings of the preferred embodiments of the invention, which, however, should not be taken to limit the invention to the specific embodiment but are only for explanation and understanding. 
     FIG. 1 is shows the relationship between a session manager and multiple application servers in a multi-user system. 
     FIG.  2 ( a ) shows an example of a prior art create-object call. 
     FIG.  2 ( b ) shows an example of a prior art open-object call. 
     FIG.  2 ( c ) shows an example of a prior art delete-object call. 
     FIG.  3 ( a ) shows a create-object call example in a system with user global name space. 
     FIG.  3 ( b ) shows an open-object call example in a system with user global name space. 
     FIG.  3 ( c ) shows a delete-object call example in a system with user global name space. 
     FIG. 4 describes the context of named resources that depend on the .EXE/.DLL overrides and on the API override values. 
     FIG. 5 is a flow diagram for creating a user and system global context. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Two important operating system (OS) features for use in a client-server distributed process system are multi-tasking and multi-user operation. 
     Multi-tasking is the ability to run more than one program at a time by dividing each task into multiple “threads” or subtasks so that distinct tasks can share a single processor by multiplexing the threads of each task. In this manner, each distinct task is given access to the processor on a shared basis. Priority based scheduling manages the processor time each task or process is allocated. 
     In an OS like Windows NT, each process is divided into multiple threads for execution. The threads are run while the processes are never run. Each process may consist of one or more threads. Each thread has an assigned priority level that can be set independently. 
     A “process” is a single group of memory addresses in which some of the addresses are allocated to program steps while the rest are allocated for data required by the program steps. Typically, processes do not share memory with other processes because each process is structured as a single entity and its memory space is protected from unauthorized access by other processes. Multiple threads are created within a process with each thread having access to all memory and other resources within the process. 
     Each thread has three possible states that include: 
     Running—when the thread is executing; 
     Ready—when thread is waiting for other threads to finish executing; and 
     Blocked—when the thread is waiting for some event to occur. 
     Because processes may have need to communicate with each other, a variety of methods are provided that include synchronization and interprocess communication objects such as: 
     Event objects for notifying a waiting thread that an event has occurred; 
     Mutex (mutual exclusion) objects for use between processes to ensure only one process has access at a time; 
     Semaphore objects for use when a counter is required for limiting the number of threads that can use a given resource; 
     Named Pipe objects are one way or duplex stream connections between two processes; and 
     Communication Port objects are message connections between two processes. 
     By associating a name with each of these objects, the objects become capable of being shared between processes. An additional named object is named shared memory that allows one process to create the named object and another to make use of it in a multi-tasking system. 
     FIG. 1 shows the architecture of a multi-user application server system  100  resident in a host system and includes a session manager  101  and and a number of application servers  200 . Each application server  200  interfaces to a client (user) workstation for running the client&#39;s application in the host system by inputting data from and providing processed data and display data to the associated client workstation. The host system contains common resources that are shared amongst the numerous client workstations through the associated application server  200 . 
     In a multi-user multi-tasking system as shown in FIG. 1, applications must be written so that more than one copy of the application can run at the same time without object name collisions occurring. However, most applications written for a single user environment implicitly assume that only one copy of the application will be active in the system at a given time. Consequently, if more than one such application were to be run at the same time in a multi-user environment, there is a reasonable probability for name collisions to occur. This would make it impractical to use many existing single user applications in a multi-user environment without modifying the application program. 
     For example, if a single user Windows NT operating system application that uses a named resource, such as a semaphore, were to attempt to run in a multi-user environment, it would initially attempt to create the named semaphore. However, if the same application had been previously started by another user, the attempt to create the named semaphore would fail. This type of application would have difficulty running multiple instances of itself in a single user environment. In order for it to run in a multi-user environment (e.g. under operating system WinFrame™), constructs must be included that localize global resources to the user level. The named resources that can run into this type of problem include: semaphores, named pipes, queues, communication ports, and named shared memory. 
     FIGS.  2 ( a,b,c ) are flow diagrams depicting the actions and results when two single-user processes (process A and process B) attempt to operate in a multi-user prior art environment. The first column (on the left) shows actions initiated by process A and the results while the second column shows the actions taken by process B and the results. The three flow diagrams are: FIG.  2 ( a ) for creating an object named “XYZ”; FIG.  2 ( b ) for opening an object named “XYZ”; and FIG.  2 ( c ) for deleting an object named “XYZ”. 
     In step  11  of FIG.  2 ( a ), application process A calls an application program interface (API) in the host systems operating system (OS) kernel for creating an object named “XYZ”. Then process B makes the same request in step  21 . In step  12 , object “XYZ” is created by the OS kernel as requested by process A and the name is stored. However, the request by process B in step  22  fails because the OS finds that the named object “XYZ” already exists. As a result process A receives the required object handle in step  13  while process B receives an error status message. 
     In FIG.  2 ( b ), both application processes A and B call an API to open the object named “XYZ”. The OS conducts a search for object “XYZ” in steps  15  and  25 . The two searches find the previously created object named “XYZ” and the object handle is returned to process A and B respectively in steps  16  and  26 . 
     In FIG.  2 ( c ) at step  17 , process A calls an A for deleting an object named “X”. Assume that process B subsequently makes the same request in step  27 . As a result, the request by process A causes a search for the object named “XYZ” in step  18  and results in the object being deleted in step  19 . Because of the earlier request to delete by process A, the search for the object named “XYZ” in step  28  fails and step  29  returns an error status message. 
     The actions and results shown in FIG.  2 ( b ) are not proper because process B gained access to object “XYZ” created by process A and not to the process named “XYZ” that was to be created by process B. Similarly, the actions and results shown in FIG.  2 ( c ) may be undesirable because an object named “XYZ” could be deleted by either process A or B as determined by which process called for the deletion first. 
     In order to accommodate Windows NT, single user applications in a multi-user WinFrame™ operating environment, the following steps are taken: 
     (1) all application program interface (API) calls by a given user for these named resources are intercepted; 
     (2) a user identifier is added to the name before it is passed on in the API call; and 
     (3) all applications running on behalf of the given user will have the named requests for resources identically modified. 
     In this manner, these named resources are made “user global” which makes them shareable only within the given user&#39;s context. 
     FIGS.  3 ( a,b,c ) steps taken to accommodate single user applications in the multi-user system and the consequence of actions taken by process A on the left and process B on the right. 
     In FIG.  3 ( a ) at step  30 , process A calls an API in the OS kernel to create an object named “XYZ”. The OS assigns ID(1) as a unique user identification (ID) associated with application process A in step  31 . In step  32 , the OS creates the object and saves the name “XYZ” together with the unique user ID(A). In step  33  the system returns the object handle to process A. Meanwhile, process B initiates similar actions in step  50  calling for the creation of an object named “XYZ” with the result that a unique user ID(B) is associated with the application process in step  51  and an object named “XYZ” is created in step  52  and the name is saved together with ID(B). The object handle for the object named “XYZ” associated with ID(B) is returned to process B. It should be noted that process A and B refer to their respective objects named “XYZ” using the same name but the OS clearly distinguishes them because of the associated user ID. 
     FIG.  3 ( b ) is a flow diagram for opening an object by process A and B. Instep  34 , process A calls an API to open an object named “XYZ”. In step  35  the unique ID that has been assigned to process A, ID(A), is retrieved by the OS and a search for the object named “XYZ” with the assigned unique user ID is made in step  36 . If a match is found for both the name “XYZ” and ID(1), step  37  returns the handle for the desired object. Step  54  initiates a similar call from application process B to open an object named “XYZ” and the OS assigns the unique user ID, ID(B), associated with process B and searches for object “XYZ” together with ID(B). Because of the unique ID assigned to each process, two same named objects can be separately supported by the OS. Consequently, step  56  searches and is able to find object “XYZ” belonging to process B. The proper object handle is returned to process B in step  57 . 
     FIG.  3 ( c ) is a flow diagram of deleting objects having the same name “XYZ”. In step  38 , process A calls an API to delete the object named “XYZ”. Again the OS retrieves the unique identifier ID(A) associated with process A in step  39  and proceeds to search for “XYZ” with matching identifier ID(A). When found, the object is deleted in step  41 . Similarly, process B calls for deletion of object “XYZ” in step  58  and the following steps  59 ,  60  and  61  result in the deletion of object “XYZ” associated with ID(B). 
     Thus, by associating a unique ID with each named object, a single user application can be used in a multi-user system without modification by using the OS modifications described above. 
     Indiscriminately applying the user identifier to API calls can lead to problems. For example, if a multi-user application uses a system semaphore to serialize access to a protected resource,sa “system global” context is needed rather than a user global context. Because the characteristics of the application making the API call are not readily available to the application program kernel, this potential problem is resolved by 
     (1) establishing user global as the default context, 
     (2) establishing a system global context, 
     (3) enabling an application to select between user global and system global context for a specific named object on an individual API basis by appending a context modifier to the name of the named object, and 
     (4) enabling the marking of specific application executable (.EXE) files or dynamically linkable library (.DLL) files so that all API calls from the executable or dynamically linked files are of the system global context. 
     In the WinFrame™ environment, multi-user applications and dynamic link libraries can intermix allocation of system global and user global named resources from within the same .EXE or .DLL. Because WinFrame™ requires that the resource type be specified at the end of the name string, accommodation of the named resource APIs require that the applications append the system global identifier to the name string. 
     FIG. 4 describes the context of named resources as a function of the user and system global modifiers applied to .EXE/.DLL and to the API call. If system global is not specified in the API call, the context is system global if .EXE/.DLL is marked system global. Otherwise, the context is user global. If the API call specifies system global, the context is system global independent of the .EXE/.DLL marking. 
     Because the client portion of an application in a distributed process client-server system generally resides at another location than the server, the server must verify the security or privilege level of the client. Also, if the client makes a request to access data in a file controlled by the server by use of an API call to open, read, or write the file, the server must have open/read/write privileges for that file. For example, if the file to be accessed by the application server is owned by the client as a user global file, access would be limited to the client. The concept of “impersonation” provides a means for resolving this dilemma. 
     Impersonation allows servers to access data on behalf of privileged clients by assuming the security level of the client. With this arrangement, a user on the network without the proper security clearance would be denied access to a file through the application server when the server attempts accessing the file by impersonating the unauthorized user. The client&#39;s APIs provide the information needed for a thread to take on the security context of the client. The named thread then receives the proper access validation. 
     Because it is possible that a multi-user server process will service requests from several single-user application processes, it is necessary that the multi-user server process be able to access the correct user global name space when referencing a named object on behalf of some single-user application process. For this purpose, the concept of user impersonation is used and extended so that impersonation not only allows the server process to assume the security context of the client process but also allows it access to the object name space of the client process. 
     A method for allowing single user applications to operate in a multi-user environment without modification of the single user application has been described. The method involves modification of the multi-user operating system by creating distinct user name spaces that have a user global context and by extending the concept of impersonation to make the user name spaces available to the application server. 
     The method described above is further summarized in the flow diagram of FIG. 5 where it is identified as method  400  for creating a coexistant user and system global context. Step  401  establishes a user global context by assigning a label to each instance of an object or application that is to be used by a single user. A single-user name space is thereby created by identifying each such instance as being globally available to the specified single-user. Step  402  enables the server process to impersonate the single-user by assuming its identity and thereby provides the server access to the single-user name space. Step  403  establishes a system global context by adding a system global identifier to each of the executable files and dynamically linkable library files. The method ends with step  404  establishing the user global context as the default context. 
     As will be understood by those skilled in the art, many changes in the methods described above may be made by the skilled practitioner without departing from the spirit and scope of the invention, which should be limited only as set forth in the claims which follow.