Added additional poll method without timeout

lib/main/concurrent/piblockingdequeue.h

@@ -136,9 +136,11 @@ public:
 	 *
 	 * @param timeoutMs how long to wait before giving up, in milliseconds
 	 * @param defaultVal value, which returns if the specified waiting time elapses before an element is available
+	 * @param isOk flag, which indicates result of method execution. It will be set to false if timeout, or true if
+	 * return value is retrieved value
 	 * @return the head of this queue, or defaultVal if the specified waiting time elapses before an element is available
 	 */
-	T poll(int timeoutMs, const T & defaultVal, bool* isOk = nullptr) {
+	T poll(int timeoutMs, const T & defaultVal = T(), bool* isOk = nullptr) {
 		T t;
 		mutex.lock();
 		bool isNotEmpty = cond_var_add->waitFor(mutex, timeoutMs, [&]() { return !PIDeque<T>::isEmpty(); });
@@ -149,6 +151,26 @@ public:
 		return t;
 	}
 
+	/**
+	 * @brief Retrieves and removes the head of this queue and return it if queue not empty, otherwise return defaultVal.
+	 * Do it immediately without waiting.
+	 *
+	 * @param defaultVal value, which returns if the specified waiting time elapses before an element is available
+	 * @param isOk flag, which indicates result of method execution. It will be set to false if timeout, or true if
+	 * return value is retrieved value
+	 * @return the head of this queue, or defaultVal if the specified waiting time elapses before an element is available
+	 */
+	T poll(const T & defaultVal = T(), bool* isOk = nullptr) {
+		T t;
+		mutex.lock();
+		bool isNotEmpty = !PIDeque<T>::isEmpty();
+		t = isNotEmpty ? T(PIDeque<T>::take_front()) : defaultVal;
+		mutex.unlock();
+		if (isNotEmpty) cond_var_rem->notifyOne();
+		if (isOk != nullptr) *isOk = isNotEmpty;
+		return t;
+	}
+
 	/**
 	 * @brief Returns the number of elements that this queue can ideally (in the absence of memory or resource
 	 * constraints) contains. This is always equal to the initial capacity of this queue less the current size of this queue.