54 lines
1.3 KiB
C
54 lines
1.3 KiB
C
/*
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* pthreads_race.c - Shows a "race condition" when multiple threads
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* try to race to modify a global value
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* Due to unpredictable behavior in context switching
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* the value of global_value does not result in what is
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* expected
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*/
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#include <pthread.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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int global_value[5] = {0};
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void *thread_routine(void *arg)
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{
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int *idx = (int *)(arg);
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for (int i = 0; i < 1000000; i++)
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{
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global_value[*idx]++;
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}
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return NULL;
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}
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int main()
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{
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// Create 5 threads
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pthread_t thr_id[5];
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int args[5] = {0, 1, 2, 3, 4};
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for (int i = 0; i < 5; i++)
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{
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if (pthread_create(&thr_id[i], NULL, thread_routine, (void *)&args[i]) == -1)
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{
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printf("COULD NOT CREATE A THREAD\n");
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exit(EXIT_FAILURE);
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}
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}
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// Wait for all threads to finish
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for (int i = 0; i < 5; i++)
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{
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pthread_join(thr_id[i], NULL);
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}
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// Print out final value of global value
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// 5 threads * 100000000 iterations - expected value is 500000000
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for (int i = 0; i < 5; i++)
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printf("PARENT READS GLOBAL: %d\n", global_value[i]);
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// Return success
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return 0;
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}
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