47 lines
789 B
Plaintext
47 lines
789 B
Plaintext
Semaphores pseudocode
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==============================
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int sem_wait(sem_t * sem);
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int sem_trywait(sem_t * sem);
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int sem_post(sem_t * sem);
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int sem_getvalue(sem_t * sem, int * sval);
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struct sem_t {
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unsigned int count;
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- current semaphore count, also used as a futex
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}
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sem_wait(sem_t *sem)
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{
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for (;;) {
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if (atomic_decrement_if_positive(sem->count))
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break;
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futex_wait(&sem->count, 0)
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}
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}
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sem_post(sem_t *sem)
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{
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n = atomic_increment(sem->count);
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// Pass the new value of sem->count
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futex_wake(&sem->count, n + 1);
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}
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sem_trywait(sem_t *sem)
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{
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if (atomic_decrement_if_positive(sem->count)) {
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return 0;
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} else {
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return EAGAIN;
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}
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}
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sem_getvalue(sem_t *sem, int *sval)
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{
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*sval = sem->count;
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read_barrier();
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}
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