decaf::util::concurrent::BlockingQueue< E > Class Template Reference

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. More...

#include <src/main/decaf/util/concurrent/BlockingQueue.h>

Inheritance diagram for decaf::util::concurrent::BlockingQueue< E >:

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Public Member Functions
virtual	~BlockingQueue ()
virtual void	put (const E &value)=0
	Inserts the specified element into this queue, waiting if necessary for space to become available.
virtual bool	offer (const E &e, long long timeout, const TimeUnit &unit)=0
	Inserts the specified element into this queue, waiting up to the specified wait time if necessary for space to become available.
virtual E	take ()=0
	Retrieves and removes the head of this queue, waiting if necessary until an element becomes available.
virtual bool	poll (E &result, long long timeout, const TimeUnit &unit)=0
	Retrieves and removes the head of this queue, waiting up to the specified wait time if necessary for an element to become available.
virtual int	remainingCapacity () const =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.
virtual int	drainTo (Collection< E > &c)=0
	Removes all available elements from this queue and adds them to the given collection.
virtual int	drainTo (Collection< E > &c, int maxElements)=0
	Removes at most the given number of available elements from this queue and adds them to the given collection.

Detailed Description

template<typename E>
class decaf::util::concurrent::BlockingQueue< E >

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 exception	Boolean Flag	Blocks	Times out
Insert	add(e)	offer(e)	put(e)	offer(e, time, unit)
Remove	remove()	poll()	take()	poll(time, unit)
Examine	element()	peek()	not applicable	not 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 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

Constructor & Destructor Documentation

template<typename E>

virtual decaf::util::concurrent::BlockingQueue< E >::~BlockingQueue ( ) [inline, virtual]

Member Function Documentation

template<typename E>

virtual int decaf::util::concurrent::BlockingQueue< E >::drainTo	(	Collection< E > &	c,
		int	maxElements
	)			`[pure virtual]`

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.

Parameters:

	c	the collection to transfer elements into
	maxElements	the maximum number of elements to transfer

Returns:: the number of elements transferred

Exceptions:

	UnsupportedOperationException	if addition of elements is not supported by the specified collection
	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

Implemented in decaf::util::concurrent::LinkedBlockingQueue< E >, decaf::util::concurrent::SynchronousQueue< E >, and decaf::util::concurrent::LinkedBlockingQueue< Pointer< Transport > >.

template<typename E>

virtual int decaf::util::concurrent::BlockingQueue< E >::drainTo ( Collection< E > & c ) [pure virtual]

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.

Parameters:

c

the collection to transfer elements into

Returns:: the number of elements transferred

Exceptions:

	UnsupportedOperationException	if addition of elements is not supported by the specified collection
	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

Implemented in decaf::util::concurrent::LinkedBlockingQueue< E >, decaf::util::concurrent::SynchronousQueue< E >, and decaf::util::concurrent::LinkedBlockingQueue< Pointer< Transport > >.

template<typename E>

virtual bool decaf::util::concurrent::BlockingQueue< E >::offer	(	const E &	e,
		long long	timeout,
		const TimeUnit &	unit
	)			`[pure virtual]`

Inserts the specified element into this queue, waiting up to the specified wait time if necessary for space to become available.

Parameters:

	e	the element to add
	timeout	how long to wait before giving up, in units of `unit`
	unit	a `TimeUnit` determining how to interpret the `timeout` parameter

Returns:: true if successful, or false if the specified waiting time elapses before space is available

Exceptions:

	InterruptedException	if interrupted while waiting
	NullPointerException	if the specified element is null
	IllegalArgumentException	if some property of the specified element prevents it from being added to this queue

Implemented in decaf::util::concurrent::LinkedBlockingQueue< E >, decaf::util::concurrent::SynchronousQueue< E >, and decaf::util::concurrent::LinkedBlockingQueue< Pointer< Transport > >.

template<typename E>

virtual bool decaf::util::concurrent::BlockingQueue< E >::poll	(	E &	result,
		long long	timeout,
		const TimeUnit &	unit
	)			`[pure virtual]`

Retrieves and removes the head of this queue, waiting up to the specified wait time if necessary for an element to become available.

Parameters:

	result	the referenced value that will be assigned the value retrieved from the Queue. Undefined if this methods returned false.
	timeout	how long to wait before giving up, in units of `unit`
	unit	a `TimeUnit` determining how to interpret the `timeout` parameter.

Returns:: true if successful or false if the specified waiting time elapses before an element is available.

Exceptions:

InterruptedException

if interrupted while waiting

Implemented in decaf::util::concurrent::LinkedBlockingQueue< E >, decaf::util::concurrent::SynchronousQueue< E >, and decaf::util::concurrent::LinkedBlockingQueue< Pointer< Transport > >.

template<typename E>

virtual void decaf::util::concurrent::BlockingQueue< E >::put ( const E & value ) [pure virtual]

Inserts the specified element into this queue, waiting if necessary for space to become available.

Parameters:

value

the element to add

Exceptions:

	InterruptedException	if interrupted while waiting
	NullPointerException	if the specified element is null
	IllegalArgumentException	if some property of the specified element prevents it from being added to this queue

Implemented in decaf::util::concurrent::LinkedBlockingQueue< E >, decaf::util::concurrent::SynchronousQueue< E >, and decaf::util::concurrent::LinkedBlockingQueue< Pointer< Transport > >.

template<typename E>

virtual int decaf::util::concurrent::BlockingQueue< E >::remainingCapacity ( ) const [pure virtual]

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.