/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ #ifndef _DECAF_UTIL_CONCURRENT_BLOCKINGQUEUE_H_ #define _DECAF_UTIL_CONCURRENT_BLOCKINGQUEUE_H_ #include #include #include #include namespace decaf { namespace util { namespace concurrent { /** * A decaf::util::Queue that additionally supports operations that wait for * the queue to become non-empty when retrieving an element, and wait for space * to become available in the queue when storing an element. * * BlockingQueue methods come in four forms, with different ways of * handling operations that cannot be satisfied immediately, but may be satisfied * at some point in the future: * one throws an exception, the second returns a special value (either * true or false, depending on the operation), the third * blocks the current thread indefinitely until the operation can succeed, * and the fourth blocks for only a given maximum time limit before giving * up. These methods are summarized in the following table: * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Throws exceptionBoolean FlagBlocksTimes out
Insert{@link #add add(e)}{@link #offer offer(e)}{@link #put put(e)}{@link #offer(Object, long, TimeUnit) offer(e, time, unit)}
Remove{@link #remove remove()}{@link #poll poll()}{@link #take take()}{@link #poll(long, TimeUnit) poll(time, unit)}
Examine{@link #element element()}{@link #peek peek()}not applicablenot applicable
* * A BlockingQueue may be capacity bounded. At any given time it may have * a remainingCapacity beyond which no additional elements can be put * without blocking. A BlockingQueue without any intrinsic capacity * constraints always reports a remaining capacity of Integer::MAX_VALUE. * * BlockingQueue implementations are designed to be used primarily for * producer-consumer queues, but additionally support {@link decaf::util::Collection} * interface. So, for example, it is possible to remove an arbitrary element from a * queue using remove(x). However, such operations are in general not * performed very efficiently, and are intended for only occasional use, such as * when a queued message is cancelled. * * BlockingQueue implementations are thread-safe. All queuing methods * achieve their effects atomically using internal locks or other forms of concurrency * control. However, the bulk Collection operations addAll, * containsAll, retainAll and removeAll are not * necessarily performed atomically unless specified otherwise in an implementation. * So it is possible, for example, for addAll(c) to fail (throwing an exception) * after adding only some of the elements in c. * * A BlockingQueue does not intrinsically support any kind of * "close" or "shutdown" operation to indicate that no more * items will be added. The needs and usage of such features tend to be * implementation-dependent. For example, a common tactic is for producers to * insert special end-of-stream or poison objects, that are * interpreted accordingly when taken by consumers. * *

* Usage example, based on a typical producer-consumer scenario. Note that a * BlockingQueue can safely be used with multiple producers and multiple * consumers. * 

     * class Producer : public Runnable {
     * private:
     *
     *     BlockingQueue* queue;
     *
     * public:
     *
     *     Producer( BlockingQueue* q ) : queue( q ) {}
     *
     *     virtual void run() {
     *         try {
     *             while( true ) { queue->put( produce() ); }
     *         } catch( InterruptedException& ex ) { ... handle ...}
     *     }
     *
     *     Object produce() { ... }
     * }
     *
     * class Consumer : public Runnable {
     * private:
     *
     *     BlockingQueue* queue;
     *
     * public:
     *
     *     Consumer( BlockingQueue* q ) : queue( q ) {}
     *
     *     virtual void run() {
     *         try {
     *             while( true ) { consume( queue->take() ); }
     *         } catch( InterruptedException& ex ) { ... handle ...}
     *     }
     *
     *     void consume( Object& x ) { ... }
     * }
     *
     * int main( int argc, char** argv ) {
     *
     *     BlockingQueue q = new SomeQueueImplementation();
     *     Producer p( &q );
     *     Consumer c1( &q );
     *     Consumer c2( &q );
     *     Thread t1( &p ).start();
     *     Thread t2( &c1 ).start();
     *     Thread t3( &c2 ).start();
     * }
     *
* *

Memory consistency effects: As with other concurrent collections, actions in a * thread prior to placing an object into a BlockingQueue happen-before * actions subsequent to the access or removal of that element from the * BlockingQueue in another thread. * * @since 1.0 */ template< typename E > class BlockingQueue : public AbstractQueue { public: virtual ~BlockingQueue() { } using Queue::offer; using Queue::poll; /** * Inserts the specified element into this queue, waiting if necessary for space * to become available. * * @param value the element to add * @throws InterruptedException if interrupted while waiting * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException if some property of the specified * element prevents it from being added to this queue */ virtual void put( const E& value ) = 0; /** * Inserts the specified element into this queue, waiting up to the specified wait * time if necessary for space to become available. * * @param e the element to add * @param timeout how long to wait before giving up, in units of * unit * @param unit a TimeUnit determining how to interpret the * timeout parameter * * @return true if successful, or false if * the specified waiting time elapses before space is available * * @throws InterruptedException if interrupted while waiting * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException if some property of the specified * element prevents it from being added to this queue */ virtual bool offer( const E& e, long long timeout, const TimeUnit& unit ) = 0; /** * Retrieves and removes the head of this queue, waiting if necessary until an * element becomes available. * * @return the head of this queue * @throws InterruptedException if interrupted while waiting */ virtual E take() = 0; /** * Retrieves and removes the head of this queue, waiting up to the specified * wait time if necessary for an element to become available. * * @param result the referenced value that will be assigned the value * retrieved from the Queue. Undefined if this methods returned false. * @param timeout how long to wait before giving up, in units of unit * @param unit a TimeUnit determining how to interpret the * timeout parameter. * @return true if successful or false if the specified * waiting time elapses before an element is available. * @throws InterruptedException if interrupted while waiting */ virtual bool poll( E& result, long long timeout, const TimeUnit& unit ) = 0; /** * Returns the number of additional elements that this queue can ideally * (in the absence of memory or resource constraints) accept without * blocking, or Integer::MAX_VALUE if there is no intrinsic * limit. * *

Note that you cannot always tell if an attempt to insert * an element will succeed by inspecting remainingCapacity * because it may be the case that another thread is about to * insert or remove an element. * * @return the remaining capacity */ virtual int remainingCapacity() const = 0; /** * Removes all available elements from this queue and adds them to the given * collection. This operation may be more efficient than repeatedly polling * this queue. A failure encountered while attempting to add elements to * collection c may result in elements being in neither, either or * both collections when the associated exception is thrown. Attempts to * drain a queue to itself result in IllegalArgumentException. * Further, the behavior of this operation is undefined if the specified * collection is modified while the operation is in progress. * * @param c the collection to transfer elements into * @return the number of elements transferred * @throws UnsupportedOperationException if addition of elements * is not supported by the specified collection * @throws IllegalArgumentException if the specified collection is this * queue, or some property of an element of this queue prevents * it from being added to the specified collection */ virtual int drainTo( Collection& c ) = 0; /** * Removes at most the given number of available elements from * this queue and adds them to the given collection. A failure * encountered while attempting to add elements to * collection c may result in elements being in neither, * either or both collections when the associated exception is * thrown. Attempts to drain a queue to itself result in * IllegalArgumentException. Further, the behavior of * this operation is undefined if the specified collection is * modified while the operation is in progress. * * @param c the collection to transfer elements into * @param maxElements the maximum number of elements to transfer * @return the number of elements transferred * @throws UnsupportedOperationException if addition of elements * is not supported by the specified collection * @throws IllegalArgumentException if the specified collection is this * queue, or some property of an element of this queue prevents * it from being added to the specified collection */ virtual int drainTo( Collection& c, int maxElements ) = 0; }; }}} #endif /* _DECAF_UTIL_CONCURRENT_BLOCKINGQUEUE_H_ */