helgrind/tests/tc03_re_excl.c

   1
   2 #include <pthread.h>
   3 #include <stdio.h>
   4 #include <stdlib.h>
   5
   6 /* Simple test program, no race: parent only modifies x after child
   7    has modified it and then joined with the parent.  Tests simple
   8    thread lifetime segment handling. */
   9
  10 /* A simple function to "use" a value, so that gcc can't
  11    possibly optimise it into nothing. */
  12 static void use ( int x ) {
  13    __asm__ __volatile__( "" : : "r"(x) : "cc","memory" );
  14 }
  15
  16 static void* worker_thread ( void* argV )
  17 {
  18   int* arg = (int*)argV;
  19   use(arg[5]); /* read access */
  20   return NULL;
  21 }
  22
  23 int main ( void )
  24 {
  25    pthread_t thread_id;
  26    volatile int* x = malloc(10 * sizeof(int));
  27    x[5] = 1;
  28    /* x[5] is Excl(parent) */
  29
  30    pthread_create(&thread_id, 0, worker_thread, (void*)x);
  31
  32    use(x[5]); /* read access */
  33
  34    /* Just before the threads join, x[5] is ShR (read by both parent
  35       and child) */
  36    pthread_join(thread_id, 0);
  37    /* x[5] is Excl(parent), because only parent and child accessed it
  38       and child has merged to parent.  So now it's ok for parent to
  39       access it without locking. */
  40
  41    x[5] = 0; /* write access */
  42
  43    return x[5];
  44 }