make queue thread-safe

README.md

@@ -8,4 +8,4 @@ It is not production-ready. Use at your own risk.
 - Hashmaps - Thread-safe (MT Safe)
 - Dynamic strings - Thread-safe (MT Safe)
   > Requires linking with the C math library (`-lm`)
-- Circular Queue - Not thread-safe (MT Unsafe)
+- Circular Queue - Thread-safe (MT Safe)

queue/myqueue.c

@@ -1,5 +1,6 @@
 #include "myqueue.h"
 
+#include <pthread.h>
 #include <stdlib.h>
 #include <string.h>
 
@@ -16,6 +17,14 @@ mcl_queue *mcl_queue_init(size_t queue_size, size_t elem_size) {
 		return NULL;
 	}
 
+	int ret = pthread_mutex_init(&queue->lock, NULL);
+	if (ret != 0) {
+		free(queue->buffer);
+		free(queue);
+
+		return NULL;
+	}
+
 	queue->front = 0;
 	queue->rear = 0;
 	queue->size = 0;
@@ -26,8 +35,15 @@ mcl_queue *mcl_queue_init(size_t queue_size, size_t elem_size) {
 }
 
 int mcl_queue_push(mcl_queue *queue, const void *elem) {
+	int ret = pthread_mutex_lock(&queue->lock);
+	if (ret != 0) {
+		return -1;
+	}
+
 	if (queue->size == queue->capacity) {
 		/* Queue full */
+		pthread_mutex_unlock(&queue->lock);
+
 		return -1;
 	}
 
@@ -38,12 +54,21 @@ int mcl_queue_push(mcl_queue *queue, const void *elem) {
 	queue->size++;
 	queue->rear = (queue->rear + 1) % queue->capacity;
 
+	pthread_mutex_unlock(&queue->lock);
+
 	return 0;
 }
 
 int mcl_queue_pop(mcl_queue *queue, void *out_elem) {
+	int ret = pthread_mutex_lock(&queue->lock);
+	if (ret != 0) {
+		return -1;
+	}
+
 	if (queue->size == 0) {
 		/* Queue empty */
+		pthread_mutex_unlock(&queue->lock);
+
 		return -1;
 	}
 
@@ -53,20 +78,41 @@ int mcl_queue_pop(mcl_queue *queue, void *out_elem) {
 	queue->front = (queue->front + 1) % queue->capacity;
 	queue->size--;
 
+	pthread_mutex_unlock(&queue->lock);
+
 	return 0;
 }
 
-void *mcl_queue_get_front(mcl_queue *queue) {
-	if (queue->size == 0) {
-		return NULL;
+int mcl_queue_get_front(mcl_queue *queue, void *out) {
+	int ret = pthread_mutex_lock(&queue->lock);
+	if (ret != 0) {
+		return -1;
 	}
 
-	return (void *)queue->buffer + (queue->front * queue->elem_size);
+	if (queue->size == 0) {
+		pthread_mutex_unlock(&queue->lock);
+
+		return -1;
+	}
+
+	void *front = (void *)queue->buffer + (queue->front * queue->elem_size);
+	memcpy(out, front, queue->elem_size);
+
+	pthread_mutex_unlock(&queue->lock);
+
+	return 0;
+}
+
+int mcl_queue_get_rear(mcl_queue *queue, void *out) {
+	int ret = pthread_mutex_lock(&queue->lock);
+	if (ret != 0) {
+		return -1;
 	}
 
-void *mcl_queue_get_rear(mcl_queue *queue) {
 	if (queue->size == 0) {
-		return NULL;
+		pthread_mutex_unlock(&queue->lock);
+
+		return -1;
 	}
 
 	size_t rear_index;
@@ -76,7 +122,12 @@ void *mcl_queue_get_rear(mcl_queue *queue) {
 		rear_index = queue->rear - 1;
 	}
 
-	return (void *)queue->buffer + (rear_index * queue->elem_size);
+	void *rear = (void *)queue->buffer + (rear_index * queue->elem_size);
+	memcpy(out, rear, queue->elem_size);
+
+	pthread_mutex_unlock(&queue->lock);
+
+	return 0;
 }
 
 void mcl_queue_free(mcl_queue *queue) {
@@ -84,6 +135,8 @@ void mcl_queue_free(mcl_queue *queue) {
 		return;
 	}
 
+	pthread_mutex_destroy(&queue->lock);
+
 	free(queue->buffer);
 	free(queue);
 }

queue/myqueue.h

@@ -1,26 +1,28 @@
 #ifndef MYCLIB_QUEUE_H
 #define MYCLIB_QUEUE_H
 
+#include <pthread.h>
 #include <stddef.h>
 
 /**
- * @brief A generic circular queue (ring buffer).
+ * @brief A simple circular queue (ring buffer).
  */
 typedef struct mcl_queue_t {
-	size_t front;	  /**< Index of the first element (read position). */
-	size_t rear;	  /**< Index where the next element will be written (write position). */
+	size_t front;		  /**< Index of the next element to read. */
+	size_t rear;		  /**< Index where the next element will be written. */
 	size_t size;		  /**< Current number of elements in the queue. */
 	size_t capacity;	  /**< Maximum number of elements the queue can hold. */
-	size_t elem_size; /**< Size in bytes of each element in the queue. */
-	void *buffer;	  /**< Pointer to the memory buffer that stores the elements. */
+	size_t elem_size;	  /**< Size in bytes of each element. */
+	void *buffer;		  /**< Memory buffer that holds the elements. */
+	pthread_mutex_t lock; /**< Mutex to protect concurrent access. */
 } mcl_queue;
 
 /**
  * @brief Create and initialize a new queue.
  *
  * @param queue_size Number of elements the queue can hold.
- * @param elem_size Size (in bytes) of each element in the queue.
- * @return Pointer to the new queue, or NULL if allocation fails.
+ * @param elem_size  Size in bytes of each element.
+ * @return Pointer to the new queue, or NULL on failure.
  */
 mcl_queue *mcl_queue_init(size_t queue_size, size_t elem_size);
 
@@ -28,8 +30,8 @@ mcl_queue *mcl_queue_init(size_t queue_size, size_t elem_size);
  * @brief Add an element to the queue.
  *
  * @param queue Pointer to the queue.
- * @param elem Pointer to the element to insert.
- * @return 0 on success, -1 if the queue is full.
+ * @param elem  Pointer to the data to add.
+ * @return 0 on success, -1 if the queue is full or on error.
  */
 int mcl_queue_push(mcl_queue *queue, const void *elem);
 
@@ -37,32 +39,34 @@ int mcl_queue_push(mcl_queue *queue, const void *elem);
  * @brief Remove an element from the queue.
  *
  * @param queue    Pointer to the queue.
- * @param out_elem Pointer where the removed element will be copied.
- * @return 0 on success, -1 if the queue is empty.
+ * @param out_elem Pointer to memory where the removed element will be copied.
+ * @return 0 on success, -1 if the queue is empty or on error.
  */
 int mcl_queue_pop(mcl_queue *queue, void *out_elem);
 
 /**
- * @brief Get a pointer to the front element of the queue (oldest one).
+ * @brief Copy the front element without removing it.
  *
  * @param queue Pointer to the queue.
- * @return Pointer to the front element, or NULL if the queue is empty.
+ * @param out   Pointer to memory where the element will be copied.
+ * @return 0 on success, -1 if the queue is empty or on error.
  */
-void *mcl_queue_get_front(mcl_queue *queue);
+int mcl_queue_get_front(mcl_queue *queue, void *out);
 
 /**
- * @brief Get a pointer to the rear element of the queue (most recently added).
+ * @brief Copy the last element without removing it.
  *
  * @param queue Pointer to the queue.
- * @return Pointer to the rear element, or NULL if the queue is empty.
+ * @param out   Pointer to memory where the element will be copied.
+ * @return 0 on success, -1 if the queue is empty or on error.
  */
-void *mcl_queue_get_rear(mcl_queue *queue);
+int mcl_queue_get_rear(mcl_queue *queue, void *out);
 
 /**
- * @brief Free all memory used by the queue.
+ * @brief Free all resources used by the queue.
  *
  * @param queue Pointer to the queue to free.
  */
 void mcl_queue_free(mcl_queue *queue);
 
-#endif
+#endif	// MYCLIB_QUEUE_H