monitor.c

#include "sync.h"

void monitor_acquire(Monitor * monitor) {
	P(monitor->mutex);
}


void monitor_release(Monitor * monitor) {
	if (sem_getvalue(monitor->next) > 0) {
		V(monitor->next);
	} else {
		V(monitor->mutex);
	}
}

queue.c

#include "sync.h"

void condition_wait(Condition * cond) {
	if (sem_getvalue(cond->monitor->next) > 0) {
		V(cond->monitor->next);
	} else {
		V(cond->monitor->mutex);
	}
	
	P(cond->queue);
	P(cond->monitor->next);
}

void condition_signal(Condition * cond) {
	if (sem_getvalue(cond->queue) > 0) {
		V(cond->queue);
	}
}

synch.h

/**
 * A monitor implementing the SIGNAL & CONTINUE model.
 */
typedef struct {
	int * waiting;
	sem_t * mutex;
	sem_t * next;
} Monitor;


/**
 * A condition bound to a monitor.
 *
 * This condition uses a shared memory segment to hold a counter and a named
 * semaphore to queue requests.
 */
typedef struct {
	int * waiting;
	Monitor * monitor;
	sem_t * queue;
} Condition;