Implement tryadd, adding itmes with a timeout

src/ucore_threadqueue.c

@@ -57,21 +57,44 @@ int uc_thread_queue_init(struct uc_threadqueue *queue, long max_elements)
     return rc;
 }
 
-int uc_thread_queue_add(struct uc_threadqueue *queue, struct uc_threadmsg *msg)
+int uc_thread_queue_tryadd(struct uc_threadqueue *queue, const struct timespec *timeout, struct uc_threadmsg *msg)
 {
+    int rc = 0;
+    struct timespec abstimeout;
+
     if (queue == NULL || msg == NULL) {
         return EINVAL;
     }
 
+    if (timeout) {
+        uc_get_absolute_time(&abstimeout, timeout);
+    }
+
     pthread_mutex_lock(&queue->mutex);
 
     //Wait if the queue is full
-    while(queue->num_elements >= queue->max_elements) {
+    while(queue->num_elements >= queue->max_elements && rc != ETIMEDOUT) {
+
         queue->num_write_waiters++;
-        pthread_cond_wait(&queue->write_cond, &queue->mutex);
+        if(timeout) {
+            //fastpath, check for a poll
+            if(timeout->tv_sec == 0 && timeout->tv_nsec == 0) {
+                rc = ETIMEDOUT;
+            } else {
+                rc = pthread_cond_timedwait(&queue->write_cond, &queue->mutex, &abstimeout);
+            }
+
+        } else {
+            pthread_cond_wait(&queue->write_cond, &queue->mutex);
+        }
         queue->num_write_waiters--;
     }
-    
+
+    if (rc == ETIMEDOUT) {
+        pthread_mutex_unlock(&queue->mutex);
+        return rc;
+    }
+ 
     //insert the new element
     msg->next = NULL;
     if (msg->msgtype >= 0) { //add at the tail