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Annotation of os2sdk/demos/examples/suspend/suspend.c, revision 1.1.1.2

1.1       root        1: /*
1.1.1.2 ! root        2:  * Example of DosSuspendThread/DosResumeThread usage.
1.1       root        3:  *
1.1.1.2 ! root        4:  * DosSuspendThread can be used to ensure mutual exclusion when a thread
        !             5:  * knows by number all the other threads which might try to access the
1.1       root        6:  * shared resource.
                      7:  * 
                      8:  * In this example the main thread can call printf() freely because it
                      9:  * knows that the only other thread has been suspended, so the main
                     10:  * thread will not be interrupted, and because it knows that the
                     11:  * subthread must have been suspended while outside of a critical
                     12:  * section, and so the main thread will not be interrupting the
                     13:  * subthread's call to vio.
                     14:  * 
                     15:  * Any thread may suspend any other thread in its process, including the
                     16:  * main thread and itself.  If a thread suspends all the threads in a
                     17:  * process, including itself, then deadlock will result, and the process
                     18:  * will have to be killed externally.
                     19:  *
                     20:  * Note that there are three methods for managing critical sections
                     21:  * amongst threads in a process:
                     22:  *
                     23:  *     1. Semaphores - this is almost always the right solution
                     24:  *     2. DosEnterCritSec
                     25:  *     3. DosSuspendThread
                     26:  *
                     27:  * compile as: cl -Gs -AL -G2 -Lp suspend.c
                     28:  *
1.1.1.2 ! root       29:  * Created by Microsoft Corp. 1986
1.1       root       30:  */
                     31: 
1.1.1.2 ! root       32: #define INCL_DOSPROCESS
        !            33: #define INCL_SUB
        !            34: 
        !            35: #include <os2def.h>
        !            36: #include <bse.h>
1.1       root       37: #include "stdio.h"
                     38: #include "malloc.h"
                     39: #define STACK_SIZE     1024
                     40: 
                     41: extern void f_thread(void);
                     42: int flag;
                     43: 
                     44: void main()
                     45: {
                     46:        char *stkptr;
1.1.1.2 ! root       47:        TID thread_id;
1.1       root       48:        register int i;
                     49:        
                     50:        /* obtain pointer to the END of a block of memory */
                     51:        stkptr = (char *)malloc(STACK_SIZE) + STACK_SIZE - 1;
                     52:        
                     53:        /* create another thread */
1.1.1.2 ! root       54:        DosCreateThread(f_thread, &thread_id, stkptr);
1.1       root       55:        
                     56:        for(i = 0; i < 20; i++) {
1.1.1.2 ! root       57:                DosSuspendThread(thread_id);    /* suspend the subthread */
1.1       root       58:        
                     59:                printf("the main thread has suspended thread %u\n", thread_id);
1.1.1.2 ! root       60:                DosSleep(3000L);
1.1       root       61:        
                     62:                /* resume the subthread */
                     63:                printf("now resuming the suspended thread\n");
1.1.1.2 ! root       64:                DosResumeThread(thread_id);
1.1       root       65: 
1.1.1.2 ! root       66:                DosSleep(3000L);
1.1       root       67:        }
1.1.1.2 ! root       68:        DosExit(EXIT_PROCESS, 0);          /* exit all threads */
1.1       root       69: }
                     70: 
                     71: void f_thread()
                     72: {
                     73:        while (1) {
1.1.1.2 ! root       74:                DosEnterCritSec();
        !            75:                VioWrtTTy("subthread running\r\n", 19, 0);
        !            76:                DosExitCritSec();
        !            77:                DosSleep(300L);
1.1       root       78:        }
                     79: }

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