Abstract:
A method for controlling parallel threads such that the speed of running programs increases and system resources are used efficiently. The method includes monitoring a number of running threads performing parallel processing and a number of standby threads that are in a standby state, and terminating standby threads in accordance with the number of the running threads and the number of the standby threads.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to multithreading, and more particularly, to a method for controlling multithreading in a system that performs parallel processing with multiple threads so as to increase the speed of programs and efficiently use system resources. 
   In a system that executes programs, such as scientific calculations, threads are used to perform parallel processing. This increases the speed of programs. An operating system (OS) program generates threads in accordance with application programs. The OS allocates system resources to each of the generated threads and runs programs associated with the threads in a parallel manner. 
   It takes time for the OS to generate a thread. Thus, once a thread is generated, the thread remains undeleted so that it can be used again. This increases the system processing speed. 
   In more detail, when a thread completes execution of a program, the OS registers the thread as a standby thread in a table. Then, if there is a request for generating the thread, the standby thread registered in the table is used to run a program. This decreases the time for generating threads. 
   In the prior art, all of the generated threads are managed as standby threads. Thus, if the number of the running threads that are actually running is small, the system would have a large number of unnecessary standby threads. This wastes memory resources since system resources are allocated to the standby threads. 
   For example, if 200 parallel threads are run at a certain time, and then only two threads are run at a later time, 198 unnecessary standby threads would be occupying the memory. This is undesirable when operating a system that has low resources and would significantly affect the speed of other programs. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a method for controlling multithreading that increases the speed of running programs and uses system resources efficiently. 
   To achieve the above object, the present invention provides a method for controlling a plurality of threads that perform parallel processing. The method includes monitoring a number of running threads performing parallel processing and a number of standby threads that are in a standby state, and terminating standby threads in accordance with the number of the running threads and the number of the standby threads. 
   The present invention also provides a controller for controlling a plurality of threads that perform parallel processing. The controller includes a thread management table for storing thread information of the plurality of threads. The thread information includes a number of running threads performing parallel processing and a number of standby threads that are in a standby state. Based on the number of the standby threads stored in the thread management table, a thread management circuit requests thread generation and a standby thread to run. A thread termination circuit terminates standby threads in accordance with the number of the running threads and the number of the standby threads stored in the thread management table. 
   The present invention further provides a computer readable storage medium storing a program for controlling a plurality of threads that perform parallel processing. The program performs a method including monitoring a number of running threads performing parallel processing and a number of standby threads that are in a standby state, and terminating standby threads in accordance with the number of the running threads and the number of the standby threads. 
   Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which: 
       FIG. 1  is a schematic block diagram of a multithreading controller according to a preferred embodiment of the present invention; 
       FIG. 2  is a schematic diagram of a thread management table of the multithreading controller of  FIG. 1 ; 
       FIG. 3  is an explanatory diagram of a thread control list of the thread management table of  FIG. 2 ; 
       FIG. 4  is a flowchart illustrating a routine for processing threads; 
       FIG. 5  is a flowchart illustrating a routine performed by a thread termination circuit of the multithreading controller of  FIG. 1 ; and 
       FIG. 6  is a schematic block diagram showing the hardware structure of the system. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  is a schematic block diagram of a multithreading controller  1  according to a preferred embodiment of the present invention. The multithreading controller  1  is incorporated in a system (computer), which runs application programs, and requests an operating system (OS)  2  to generate threads. The controller  1  uses the generated threads to run program sections (e.g., DO loop or subroutines) in parallel. 
   When a thread completes running a program section, the multithreading controller  1  registers the thread as a standby thread. Subsequently, when there is a request to perform the program section, the multithread controller  1  searches for the corresponding standby thread and, when finding the desired standby thread, runs the program section with the standby thread. If the desired standby thread is not found, the controller  1  requests the OS 2 to generate a thread. 
   The multithreading controller  1  monitors the number of threads that are running program sections (hereafter referred to as running thread number) and the number of standby threads (hereafter referred to as standby thread number). The multithreading controller  1  terminates the surplus standby threads when the standby thread number exceeds the number of necessary standby threads relative to the running thread number. The multithreading controller  1  terminates standby threads based on, for example, a maximum running thread number and the standby thread number. 
   In more detail, the multithreading controller  1  monitors the running thread number for a predetermined time period, and sets the necessary number of standby threads to the maximum value of the running thread number (maximum running thread number) taken during the time period. Then, the multithreading controller  1  compares the maximum running thread number with the currently managed number of standby threads. If the standby thread number is greater than the maximum running thread number, the multithreading controller  1  terminates the excessive standby threads. In other words, the multithreading controller  1  decreases the standby thread number until it matches the maximum running thread number. 
   In this manner, the multithreading controller  1  decreases the standby threads that are using the system resources in a wasteful manner. Thus, the running threads are unaffected by surplus standby threads. 
   The maximum running thread number varies in accordance with the operational state of the system. Hence, by terminating standby threads in accordance with changes in the maximum running thread number, the standby threads are managed at an optimal number with respect to the operational state. 
   Since the number of standby threads correspond to the maximum running thread number, which is obtained by monitoring the running thread number over a predetermined time period, sudden increases in the number of threads can be handled. That is, even if the running thread number decreases momentarily, a number of standby threads corresponding to the maximum running thread number are stored. This avoids the termination of too many standby threads and enables programs to run immediately. 
   The structure of the multithreading controller will now be discussed. 
   The multithreading controller  1  includes a thread management circuit  11 , a thread termination circuit  12 , and a thread management table  13 . 
   The thread management circuit  11  requests the OS 2 to generate a thread and requests a thread to run a program. The thread termination circuit  12  monitors the standby threads and deletes surplus standby threads. 
   Three threads  14 ,  15 ,  16 , which have been generated by the OS 2, are illustrated in  FIG. 1 . The first two threads  14 ,  15  are running threads, which run programs, and the third thread  16  is a standby thread, which has completed a program. 
     FIG. 2  is a schematic diagram of the thread management table  13 . The thread management table  13  includes an information management table  21  and a plurality (three in association with the threads  14  to  16  in  FIG. 1 ) of thread control lists  22 ,  23 ,  24 . The information management table  21  has a running thread queue section  21   a , a standby thread queue section  21   b , a standby thread counter section  21   c , a running thread counter section  21   d , and a maximum running thread counter section  21   e.    
   The running thread queue section  21   a  stores addresses of the thread control table lists that correspond to the queued running threads. Further, the running thread queue section  21   a  manages information concerning the running threads. 
   The standby thread queue section  21   b  stores addresses of the thread control table lists that correspond to the queued standby threads. Further, the standby thread queue section  21   b  manages information concerning the standby threads. Accordingly, the running thread queue section  21   a  records the addresses of the thread control lists  22 ,  23  associated with the running threads  14 ,  15 , and the standby thread queue section  21   b  records the address of the thread control list  24  associated with the standby thread  16 . 
     FIG. 3  is an explanatory diagram illustrating the structure of the thread control list  24 . The other thread control lists  22 ,  23  have a structure similar to the thread control list  24  and will thus not be discussed. 
   The thread control list  24  includes a thread running event control block (ECB)  24   a  and a thread terminating ECB  24   b . The thread running ECB  24   a  manages the requests received from the thread management circuit  11 . The thread terminating ECB  24   b  manages termination requests received from the thread termination circuit  12  of  FIG. 1 . The standby thread  16  runs or stops a program in accordance with information written to the ECBs  24   a ,  24   b.    
   The thread management circuit  11  stores a run request in the thread running ECB  24   a  of the thread control list  24  associated with the standby thread queue section  21   b . When the run request stored in the thread running ECB  24   a  is associated with the standby thread  16 , the standby thread  16  runs the program associated with the standby thread  16  in accordance with the information. 
   The thread termination circuit  12  stores a termination request in the thread terminating ECB  24   b  of the thread control list  24  associated with the standby thread queue section  21   b . When the termination request stored in the thread terminating ECB  24   b  is associated with the standby thread  16 , the standby thread  16  is terminated. This frees the system resources that were allocated to the standby thread  16 . 
   The standby thread counter section  21   c  stores the number of standby threads counted by a standby thread counter (not shown). The running thread counter section  21   d  stores the number of running threads counted by a running thread counter (not shown). The maximum running thread counter section  21   e  stores a maximum value of the number of running threads counted by a maximum running thread counter (not shown). 
   When the running threads  14 ,  15  complete the associated programs, the running thread counter decrements by one the value of the running thread counter section  21   d  for each of the running threads  14 ,  15 . Further, the standby thread counter increments by one the value of the standby thread counter section  21   c  for each of the running threads  14 ,  15 . 
   When the standby thread  16  receives a run request from the thread management circuit  11 , the value of the standby thread counter section  21   c  is decremented by one, and the value of the running thread counter section  21   d  is incremented by one. If the value of the running thread counter section  21   d  is greater than that of the maximum running thread counter section  21   e , the standby thread  16  updates the value of the maximum running thread counter section  21   e  to the value of the running thread counter section  21   d.    
   The thread management circuit  11  requests the generation or running of a thread based on the data of the standby thread counter section  21   c . More specifically, when the thread management circuit  11  receives a request for running a parallel program, the thread management circuit  11  requests the OS 2 to generate a thread if the value of the standby thread counter section  21   c  is null. The thread management circuit  11  queues the generated thread in the running thread queue section  21   a  and requests the thread to run a program. If the value of the standby thread counter section  21   c  is one or greater, the thread management circuit  11  requests the standby thread  16  queued in the standby thread queue section  21   b  to run a program. 
   Based on the values of the standby thread counter section  21   c  and the maximum running thread counter section  21   e , the thread termination circuit  12  deletes surplus threads. In other words, the thread termination circuit  12  monitors the maximum running thread counter section  21   e  and the standby thread counter section  21   c  at predetermined time intervals and compares the values of the two counter sections  21   c ,  21   e . If the value of the standby thread counter section  21   c  is greater than that of the maximum running thread counter section  21   e , the thread termination circuit  12  terminates the standby threads until the number of the standby threads becomes equal to the value of the maximum running thread counter section  21   e . More specifically, the thread termination circuit  12  requests termination of a number of standby threads exceeding the value of the maximum running thread counter section to recover system resources. 
   The operation of the threads  14  to  16  and the thread termination circuit  12  will now be discussed.  FIG. 4  is a flowchart illustrating a routine performed by a thread (running thread or standby thread). 
   When entering the routine, at step S 31 , the thread first increments the value of the running thread counter section  21   d  by one. 
   At step S 32 , the thread compares the value of the running thread counter section  21   d  with the value of the maximum running thread counter section  21   e . If the value of the running thread counter section  21   d  is greater than that of the maximum running thread counter section  21   e , the thread proceeds to step S 33 . At step S 33 , the thread updates the value of the maximum running thread counter section  21   e  to that of the running thread counter section  21   d.    
   At step S 34 , the thread runs a program. When the program is completed, the thread proceeds to step S 35 . 
   At step S 35 , the thread decrements the running thread counter section  21   d  by one. Next, at step S 36 , the thread increments the value of the standby thread counter section  21   c  by one. At step S 37 , the thread queues the corresponding thread control list in the standby thread queue section  21   b.    
   At step S 38 , the thread (standby thread) performs a multi-wait process. In the multi-wait process, the thread monitors the thread running ECB  24   a  and the thread terminating ECB  24   b  and waits until information is written to one of the two ECBs  24   a ,  24   b . When information is written to the thread running ECB  24   a  or the thread terminating ECB  24   b , the thread proceeds to step S 39 . 
   At step S 39 , the thread determines whether the information written in step S 38  is a termination request. If the written information is not a termination request, that is, if the information is a run request, the thread proceeds to step S 40 . At step S 40 , the thread increments the standby thread counter section  21   c  by one. The thread then returns to step S 31 . As a result, the thread functions as a running thread, which runs a program, and the standby thread is recycled. 
   If the written information is a termination request in step S 39 , the thread proceeds to step S 41 . At step S 41 , the standby thread undergoes a termination process. This terminates (deletes) the standby thread. 
     FIG. 5  is a flowchart showing a routine performed by the thread termination circuit  12 . 
   At step S 51 , the thread termination circuit  12  sets a timer to time a predetermined time. The predetermined time is the time period during which the values of the standby thread counter section  21   c  and the maximum running thread counter section  21   e  is monitored. The monitoring time may be fixed in accordance with the system or varied in accordance with the operating time of the system. When the predetermined time elapses, the thread termination circuit  12  proceeds to step S 52 . 
   At step S 52 , the thread termination circuit  12  compares the values of the standby thread counter section  21   c  and the maximum running thread counter section  21   e  to determine whether the maximum running thread number is greater than the standby thread number. If the maximum running thread number is greater than the standby thread number, the thread termination circuit  12  returns to step S 51 . If the standby thread number is greater than the maximum running thread number, the thread termination circuit  12  proceeds to step S 53 . 
   At step S 53 , the thread termination circuit  12  requests termination of a standby thread (writes a termination request to the thread terminating ECB  24   b  of the thread control list corresponding to the standby thread) to terminate the standby thread and recover memory resources. 
   The multithreading controller  1  may also be embodied in a computer program executed by a computer.  FIG. 6  shows a computer  60 , which performs multithreading to run programs in parallel. The computer  60  includes a processor  61 , an input/output device  62 , a main memory  63 , and an auxiliary memory  64 . 
   The computer program is stored in a portable storage medium  65 , such as a floppy disk or a CD-ROM. Alternatively, the computer program may be stored in a main memory or an auxiliary memory of another network-connected computer. 
   The computer program is loaded to the main memory  63  of the computer  60  after the computer program is temporarily copied or installed to the auxiliary memory  64  from the storage medium  65 . Alternatively, the computer program is loaded directly to the main memory  63  from the storage medium  65 . Afterward, the program is executed. The thread management table  13  of  FIG. 1  is generated in the main memory  63 , and the thread management table  13  manages thread information. 
   Further, when a computer program is provided from another device that is connected to a network, the program is first received via the network from the device. The program is then either directly stored in the main memory  63  or temporarily copied or installed in the auxiliary memory  64  and then loaded to the main memory  63 . Afterward, the program is run. 
   The devices  61 – 64  shown in  FIG. 6  may be replaced by elements that perform the same function when the computer program is run. Further, the computer program may be used in a system having a plurality of each of the devices  61 – 64 . Additionally, the computer program may be used in a loosely-coupled or tightly-coupled computer system. 
   The multithreading controller  1  has the advantages described below. 
   (1) The thread termination circuit  12  of the multithreading controller  1  monitors the number of running threads over a predetermined time period and compares the maximum value obtained during the time period (maximum running thread number) with the standby thread number. When the standby thread number is greater than the maximum running thread number, the surplus standby threads, the number of which exceeds the maximum running thread number, are terminated. This recovers the system resources that were used insufficiently by the standby threads and decreases the effects on the running threads of such surplus standby threads. 
   (2) The thread termination circuit  12  keeps a number of standby threads corresponding to the value of the maximum running thread counter section  21   e , or the maximum number of standby threads corresponding to the number running threads obtained during the predetermined time, and terminates the remaining, surplus standby threads. The maximum running thread number varies in accordance with the state of the running programs, or the operational state of the system. Since the standby threads are terminated in accordance with the changes in the maximum running thread number, the necessary number of standby threads are ensured in accordance with the operational state of the system. 
   It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the present invention may be embodied in the following forms. 
   The value of the standby thread counter section  21   c  may be the currently necessary number of standby threads. In this case, standby threads may be terminated based on a comparison between the value of the standby thread counter section  21   c  and the value of the running thread counter section  21   d . Alternatively, an average value of the number of the running threads during a predetermined time period may be obtained as the necessary number of standby threads. In this case, standby threads are terminated based on a comparison between the average value and the current number of running threads until the number of the standby threads decreases to the average value or the present running thread number. 
   The necessary number of standby threads may be obtained by multiplying the running thread number by a coefficient, which is a fixed value or a value obtained in accordance with the state of the system. In this case, standby threads are terminated until the number of standby threads decreases to the necessary number. 
   The thread management circuit  11  or the thread termination circuit  12  may be configured to update the value of the maximum running thread counter section (maximum running thread counter section  21   e ). 
   The present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.