80 lines
1.6 KiB
C
80 lines
1.6 KiB
C
/*
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* con2.c - Concurrency using flag array - version 1
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* Allows threads to specify desire for critical secgion
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* Due to race conditions with the flag array, it cannot guarentee mutual exclusion
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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 <sys/types.h>
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#include <unistd.h>
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// shared global
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static int counter1 = 0;
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static int counter2 = 0;
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// start flag
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volatile int start = 0;
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// flag array
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volatile int flag[2] = {0, 0};
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void *thread_routine(void *args)
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{
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int me = *((int *)args);
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int you = me ? 0 : 1;
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printf("Worker thread: %d ready, you are %d\n", me, you);
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// wait for start from master thread
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while (!start)
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;
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for (int j = 0; j < 100000000; j++)
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{
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while (flag[you])
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{
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/* do nothing */
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}
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flag[me] = 1;
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// this is the critical section
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counter1++;
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counter2++;
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// leaving critical section
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flag[me] = 0;
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}
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printf("Worker thread: %d done\n", me);
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return NULL;
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}
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int main()
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{
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int val1 = 0;
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int val2 = 1;
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pthread_t thr1;
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pthread_t thr2;
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if (pthread_create(&thr1, NULL, thread_routine, (void *)&val1) == -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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if (pthread_create(&thr2, NULL, thread_routine, (void *)&val2) == -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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start = 1;
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pthread_join(thr1, NULL);
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pthread_join(thr2, NULL);
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printf("counter1: %d\n", counter1);
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printf("counter2: %d\n", counter2);
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return EXIT_SUCCESS;
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}
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