helgrind/tests/tc21_pthonce.c

   1
   2 /* This really exists to check that Thrcheck behaves plausibly
   3    with pthread_once calls.  Which it appears to.
   4
   5    The original source of this program is as shown below, although it
   6    has been modified somewhat.  See
   7    http://www.oreilly.com/pub/a/oreilly/ask_tim/2001/codepolicy.html
   8    for OReilly's policy on using bits of their code examples.
   9 */
  10
  11
  12 /********************************************************
  13  * An example source module to accompany...
  14  *
  15  * "Using POSIX Threads: Programming with Pthreads"
  16  *     by Brad Nichols, Dick Buttlar, Jackie Farrell
  17  *     O'Reilly & Associates, Inc.
  18  *
  19  ********************************************************
  20  * once_exam.c
  21  *
  22  * An example of using the pthreads_once() call to execute an
  23  * initialization procedure.
  24  *
  25  * A program spawns multiple threads and each one tries to
  26  * execute the routine welcome() using the once call. Only
  27  * the first thread into the once routine will actually
  28  * execute welcome().
  29  *
  30  * The program's main thread synchronizes its exit with the
  31  * exit of the threads using the pthread_join() operation.
  32  *
  33 */
  34
  35 #include <stdlib.h>
  36 #include <stdio.h>
  37 #include <unistd.h>
  38 #include <sys/types.h>
  39 #include <assert.h>
  40
  41 #include <pthread.h>
  42
  43 /* With more than 2 threads, the precise error reports vary between
  44    platforms, in terms of the number of races detected.  Make life
  45    simple and just have 2 threads and so just 1 race. */
  46 #define  NUM_THREADS 2
  47
  48 static pthread_once_t welcome_once_block = PTHREAD_ONCE_INIT;
  49
  50 static int unprotected1 = 0;
  51 static int unprotected2 = 0;
  52
  53 /* This is a hack: delay threads except the first enough so as to
  54    ensure threads[0] gets to the pthread_once call first.  This is so
  55    as to ensure that this test produces results which aren't
  56    scheduling sensitive.  (sigh) */
  57 void maybe_stall ( int myid )
  58 {
  59    assert(myid >= 0 && myid < NUM_THREADS);
  60    if (myid > 0)
  61       sleep(1);
  62 }
  63
  64 void welcome(void) {
  65    printf("welcome: Welcome\n");
  66    unprotected1++; /* this is harmless */
  67 }
  68
  69 void* child ( void* argV ) {
  70    int r;
  71    maybe_stall( *(int*)argV );
  72    r= pthread_once(&welcome_once_block, welcome); assert(!r);
  73    printf("child: Hi, I'm thread %d\n", *(int*)argV);
  74    unprotected2++; /* whereas this is a race */
  75    return NULL;
  76 }
  77
  78 int main ( void ) {
  79    int       *id_arg, i, r;
  80    pthread_t threads[NUM_THREADS];
  81
  82    id_arg = (int *)malloc(NUM_THREADS*sizeof(int));
  83
  84    printf("main: Hello\n");
  85    for (i = 0; i < NUM_THREADS; i++) {
  86       id_arg[i] = i;
  87       r= pthread_create(&threads[i], NULL, child, &id_arg[i]);
  88       assert(!r);
  89    }
  90
  91    for (i = 0; i < NUM_THREADS; i++) {
  92       pthread_join(threads[i], NULL);
  93       /* printf("main: joined to thread %d\n", i); */
  94    }
  95    printf("main: Goodbye\n");
  96    return 0;
  97 }