Recursive Mutex

RecursiveMutex/RecursiveMutex.c

@@ -0,0 +1,131 @@
+#include "RecursiveMutex.h"
+#include <stdlib.h>
+#include <assert.h>
+
+void
+rec_mutex_init(rec_mutex_t* mutex) {
+
+	/* No lock till by same thread*/
+	mutex->nLocks = 0;
+
+	/* No lock by any thread*/
+	mutex->lockingThread = 0;
+
+	/* initialising cv */
+	pthread_cond_init(&mutex->cv, NULL);
+
+	/* initialising state mutex*/
+	pthread_mutex_init(&mutex->stateMutex, NULL);
+
+	/* No blocked threads till now*/
+	mutex->nWaited = 0;
+}
+
+void
+rec_mutex_lock(rec_mutex_t* mutex) {
+
+	pthread_mutex_lock(&mutex->stateMutex);
+	/* Case 1 : No lock is applied till now */
+	if (mutex->nLocks == 0) {
+		mutex->lockingThread = pthread_self();
+		mutex->nLocks=1;
+		pthread_mutex_unlock(&mutex->stateMutex);
+		return;
+	}
+	/* Case 2 : Locked is applied by same thread */
+	if (mutex->lockingThread == pthread_self()) {
+
+		if (mutex->nLocks == 0) {
+			printf("No self locking. Thread is applying lock for first time.\n");
+			exit(EXIT_FAILURE);
+		}
+
+		mutex->nLocks++;
+		pthread_mutex_unlock(&mutex->stateMutex);
+		return;
+	}
+	/* Case 3 : Different thread is trying to apply
+	the lock */
+
+	while (mutex->lockingThread && mutex->lockingThread != pthread_self()) {
+
+		mutex->nWaited++;
+		pthread_cond_wait(&mutex->cv, &mutex->stateMutex);
+		mutex->nWaited--;
+	}
+
+	/* Another thread trying to applying lock after 
+	the owner thread unlocked all its locks on mutexes.*/
+	if (mutex->nLocks != 0 || 
+		mutex->lockingThread != 0 ) {
+		printf("Locks is still on rec mutex and another thread is trying to apply a lock.\n");
+		exit(EXIT_FAILURE);
+	}
+
+	mutex->nLocks = 1;
+	mutex->lockingThread = pthread_self();
+	pthread_mutex_unlock(&mutex->stateMutex);
+
+}
+
+void
+rec_mutex_unlock(rec_mutex_t* mutex) {
+
+	pthread_mutex_lock(&mutex->stateMutex);
+	/* Case 1 : No lock is currently on recursive mutex.*/
+	if (mutex->nLocks == 0 || mutex->lockingThread == 0) {
+		printf("No lock is present on the rec mutex.\n");
+		exit(EXIT_FAILURE);
+	}
+
+	/* Case 2 : Unlocking by same thread. */
+	if (mutex->lockingThread == pthread_self()) {
+
+		assert(mutex->nLocks > 0);
+
+		mutex->nLocks--;
+
+		if (mutex->nLocks > 0) {
+			pthread_mutex_unlock(&mutex->stateMutex);
+			return;
+		}
+
+		mutex->lockingThread = 0;
+		if (mutex->nWaited > 0) {
+			pthread_cond_signal(&mutex->cv);
+		}
+
+		pthread_mutex_unlock(&mutex->stateMutex);
+		return;
+	}
+
+	/* Case 3 : Unlocking attempt by different thread. */
+
+	while (mutex->lockingThread && mutex->lockingThread != pthread_self()) {
+		assert(0);
+	}
+
+	pthread_mutex_unlock(&mutex->stateMutex);
+}
+
+void
+rec_mutex_destroy(rec_mutex_t* mutex) {
+	if (mutex->nLocks > 0) {
+		printf("Mutex is still locked by live thread.\n");
+		exit(EXIT_FAILURE);
+	}
+
+	if (mutex->lockingThread != 0) {
+		printf("Mutex is still locked by live thread.\n");
+		exit(EXIT_FAILURE);
+	}
+
+	if (mutex->nWaited > 0) {
+		printf("There is some blocked state.\n");
+		exit(EXIT_FAILURE);
+	}
+
+	pthread_mutex_destroy(&mutex->stateMutex);
+
+	pthread_cond_destroy(&mutex->cv);
+}