43 lines
854 B
C
43 lines
854 B
C
#include <pthread.h>
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#include <inttypes.h>
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#include <assert.h>
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#include <stdio.h>
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#define RUNS (4096 * 256)
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#define THREADS 4
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static int counter = 0;
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void* count(void* null) {
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for (int r = 0; r < RUNS; r++) {
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counter++;
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// Equivalent to:
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//
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// int local = counter;
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// counter = local + 1;
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//
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// This is not thread-safe as the increment is not atomic.
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// **Incorrect**
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}
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}
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int main() {
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pthread_t handlers[THREADS];
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for (intptr_t i = 0; i < THREADS; i++) {
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int res = pthread_create(&handlers[i], NULL, count, NULL);
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assert(!res);
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}
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for (int i = 0; i < THREADS; i++) {
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int res = pthread_join(handlers[i], NULL);
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assert(!res);
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}
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if (counter != RUNS * THREADS) {
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printf("Didn't count so well. :/, found %d\n", counter);
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} else {
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printf("Counted up to %d.\n", counter);
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}
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}
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