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 } 45
