90 lines
2.3 KiB
C
90 lines
2.3 KiB
C
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#include <assert.h>
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#include <inttypes.h>
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#include <pthread.h>
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#include <semaphore.h>
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#include <stdio.h>
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#include <stdint.h>
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#include <stdlib.h>
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// Use the struct here for passing arguments to the runner() threads.
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// All instances of this struct should point to the same pthread_mutex_t
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// and shared variables.
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typedef struct args {
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pthread_mutex_t *lock;
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int64_t *shared;
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} arg_t;
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/* Function to run in concurrent threads. The argument passed should be a
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pointer to a pthread_mutex_t to be used for mutual exclusion. Within the
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nested for-loop structure, use the mutex to protect the the increments
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and decrements of the shared variable. To get the timing right for the
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unit tests, experiment with placing the lock/unlock calls in different
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places (e.g., around both for-loops, inside the outer one, inside the
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inner one, etc.) */
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void *
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runner (void *arg)
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{
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// Retrieve the shared pointer and mutex from the passed struct.
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arg_t *args = (arg_t *) arg;
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pthread_mutex_t *lock = args->lock;
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int64_t *shared = args->shared;
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for (int j = 0; j < 1000000; j++)
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{
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pthread_mutex_lock (lock);
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for (int i = 0; i < 100; i++)
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{
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*shared += 1;
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*shared -= 1;
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}
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pthread_mutex_unlock (lock);
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}
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pthread_exit (NULL);
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}
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/* Simple fork-join routine that creates two threads running the runner()
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function above. Pass the lock and a pointer to the shared variable to
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both threads. When both threads complete, return the shared variable,
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which should have a value of 0.
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*/
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int64_t
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run (void)
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{
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int64_t shared = 0;
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pthread_mutex_t lock;
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if (pthread_mutex_init (&lock, NULL) != 0)
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{
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fprintf (stderr, "Failed to initialize mutex\n");
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return shared;
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}
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arg_t args;
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args.lock = &lock;
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args.shared = &shared;
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pthread_t t1, t2;
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if (pthread_create (&t1, NULL, runner, &args) != 0)
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{
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fprintf (stderr, "Failed to create thread 1\n");
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pthread_mutex_destroy (&lock);
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return shared;
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}
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if (pthread_create (&t2, NULL, runner, &args) != 0)
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{
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fprintf (stderr, "Failed to create thread 2\n");
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pthread_cancel (t1);
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pthread_join (t1, NULL);
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pthread_mutex_destroy (&lock);
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return shared;
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}
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pthread_join (t1, NULL);
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pthread_join (t2, NULL);
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pthread_mutex_destroy (&lock);
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return shared;
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}
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