Queue objects provide a blocking, thread-safe message-passing object to Qore programs More...

#include <QC_Queue.dox.h>

Public Member Methods
nothing	clear ()
	Clears the Queue of all data. More...

	clearError ()
	clears the error setting from the Queue; if error information is set, then after this call, the Queue is usable again More...

	constructor (int max=-1)
	Creates the Queue object. More...

	copy ()
	Creates a new Queue object with the same elements and maximum size as the original.

	destructor ()
	Destroys the Queue object. More...

bool	empty ()
	Returns True if the Queue is empty, False if not. More...

auto	get (timeout timeout_ms=0)
	Blocks until at least one entry is available on the queue, then returns the first entry in the queue. If a timeout occurs, an exception is thrown. If the timeout value equal to zero, then the call does not timeout until data is available, while negative timeout values cause the call to timeout immediately if the call would otherwise block. More...

int	getReadWaiting ()
	Returns the number of threads currently blocked on this queue for reading. More...

int	getWaiting ()
	Returns the number of threads currently blocked on this queue for reading. More...

int	getWriteWaiting ()
	Returns the number of threads currently blocked on this queue for writing. More...

nothing	insert (auto arg, timeout timeout_ms=0)
	Inserts a value at the beginning of the queue. More...

int	max ()
	Returns the upper limit of the number of elements in the Queue. More...

auto	pop (timeout timeout_ms=0)
	Blocks until at least one entry is available on the queue, then returns the last entry in the queue. If a timeout occurs, an exception is thrown. If the timeout is less than or equal to zero, then the call does not timeout until data is available. More...

nothing	push (auto arg, timeout timeout_ms=0)
	Pushes a value on the end of the queue. More...

	setError (string err, string desc)
	sets an error status on the Queue and clears the Queue; while a Queue object has an error status, any write operations to the queue will fail and cause an exception to be raised with the information provided to this method More...

int	size ()
	Returns the number of elements in the Queue. More...

Detailed Description

Queue objects provide a blocking, thread-safe message-passing object to Qore programs

Restrictions:: Qore::PO_NO_THREAD_CLASSES

Queue objects can also be used as a stack or as a blocking message channel, if a maximum size is given to Queue::constructor() when the object is created.
In this case when the Queue is full, adding new elements to the Queue will block until the Queue shrinks below the maximum size.
All read and write methods to Queue also take timeout values; if a timeout occurs a QUEUE-TIMEOUT exception is thrown.

Queues can be atomically flagged with an error status by calling Queue::setError(). This method will cause any write operations on the Queue to fail with the error information provided with this call. Calling Queue::clearError() causes the error status to be removed and allows the Queue to be usable again.

Note: This class is not available with the PO_NO_THREAD_CLASSES parse option

Member Function Documentation

◆ clear()

nothing Qore::Thread::Queue::clear ( )

Clears the Queue of all data.

Example:: queue.clear();

Note: This method does not throw any exceptions, but exceptions could be thrown by in destructors of objects that go out of scope by being removed from the Queue

◆ clearError()

Qore::Thread::Queue::clearError ( )

clears the error setting from the Queue; if error information is set, then after this call, the Queue is usable again

Example:: queue.clearError()

See also: setError()

Since: Qore 0.8.12

◆ constructor()

Qore::Thread::Queue::constructor ( int max = -1 )

Creates the Queue object.

Example:: Queue queue();

Parameters

max	the maximum size of the Queue; -1 means no limit; if 0 or a negative number other than -1 is passed then a `QUEUE-SIZE-ERROR` exception will be thrown

Exceptions

QUEUE-SIZE-ERROR the size cannot be zero or any negative number except for -1 or a number that cannot fit in 32 bits (signed)

See also: Queue::max()

Since: Qore 0.8.4 this method takes a maximum size parameter and can throw exceptions if the parameter is invalid

◆ destructor()

Qore::Thread::Queue::destructor ( )

Destroys the Queue object.

Note: It is a programming error to delete this object while other threads are blocked on it; in this case an exception is thrown in the deleting thread, and also in each thread blocked on this object when it is deleted

Exceptions

QUEUE-ERROR The queue was deleted while at least one thread was blocked on it

◆ empty()

bool Qore::Thread::Queue::empty ( )

Returns True if the Queue is empty, False if not.

Code Flags:: CONSTANT

Example:: bool b = queue.empty();

Returns: True if the Queue is empty, False if not

See also: Queue::size()

Since: Qore 0.8.8

◆ get()

auto Qore::Thread::Queue::get ( timeout timeout_ms = 0 )

Blocks until at least one entry is available on the queue, then returns the first entry in the queue. If a timeout occurs, an exception is thrown. If the timeout value equal to zero, then the call does not timeout until data is available, while negative timeout values cause the call to timeout immediately if the call would otherwise block.

Example:: auto data = queue.get();

Parameters

timeout_ms a timeout value to wait for data to become available on the queue; integers are interpreted as milliseconds; relative date/time values are interpreted literally with a maximum resolution of milliseconds. A negative timeout value causes the call to time out immediately with a QUEUE-TIMEOUT exception if the call would otherwise block. If a positive timeout argument is passed, and no data is available in the timeout period, a "QUEUE-TIMEOUT" exception is thrown. If no value or a value that converts to integer 0 is passed as the argument, then the call does not timeout until data is available on the queue.

Returns: the first entry on the queue

Note: This method throws a "QUEUE-TIMEOUT" exception on timeout, in order to enable the case where NOTHING was pushed on the queue to be differentiated from a timeout

Exceptions

QUEUE-TIMEOUT	The timeout value was exceeded
QUEUE-ERROR	The queue was deleted while at least one thread was blocked on it
QUEUE-TIMEOUT-ERROR	the timeout value must be >= -2147483648 and <= 2147483647 or this exception is thrown

◆ getReadWaiting()

int Qore::Thread::Queue::getReadWaiting ( )

Returns the number of threads currently blocked on this queue for reading.

This is a "synonym" for Queue::getWaiting()

Code Flags:: CONSTANT

Example:: int waiting = queue.numReadWaiting();

Returns: the number of threads currently blocked on this queue for reading

See also: Queue::getWriteWaiting()

Since: Qore 0.8.4

◆ getWaiting()

int Qore::Thread::Queue::getWaiting ( )

Returns the number of threads currently blocked on this queue for reading.

This is a "synonym" for Queue::getReadWaiting()

Code Flags:: CONSTANT

Example:: int waiting = queue.numWaiting();

Returns: the number of threads currently blocked on this queue for reading

See also: Queue::getWriteWaiting()

◆ getWriteWaiting()

int Qore::Thread::Queue::getWriteWaiting ( )

Returns the number of threads currently blocked on this queue for writing.

Code Flags:: CONSTANT

Example:: int waiting = queue.getWriteWaiting();

Returns: the number of threads currently blocked on this queue for writing

See also: Queue::getReadWaiting()

Since: Qore 0.8.4

◆ insert()

nothing Qore::Thread::Queue::insert	(	auto	arg,
		timeout	timeout_ms = `0`
	)

Inserts a value at the beginning of the queue.

Example:: queue.insert(value);

Parameters

arg value to be put on the queue

timeout_ms a timeout value to wait for a free entry to become available on the queue; integers are interpreted as milliseconds; relative date/time values are interpreted literally with a maximum resolution of milliseconds. A negative timeout value causes the call to time out immediately with a QUEUE-TIMEOUT exception if the call would otherwise block. If a positive timeout argument is passed, and the queue has already reached its maximum size and does not go below the maximum size within the timeout period, a "QUEUE-TIMEOUT" exception is thrown. If no value or a value that converts to integer 0 is passed as the argument, then the call does not timeout until a slot becomes available on the queue. Queue slots are only limited if a maximum size is passed to Queue::constructor().

Exceptions

QUEUE-TIMEOUT	The timeout value was exceeded
QUEUE-ERROR	The queue was deleted while at least one thread was blocked on it
QUEUE-TIMEOUT-ERROR	the timeout value must be >= -2147483648 and <= 2147483647 or this exception is thrown

Since: Qore 0.8.4 this method takes a timeout parameter

◆ max()

int Qore::Thread::Queue::max ( )

Returns the upper limit of the number of elements in the Queue.

Code Flags:: CONSTANT

Example:: int max = queue.max();

Returns: the upper limit of the number of elements in the Queu

See also: Queue::size()

◆ pop()

auto Qore::Thread::Queue::pop ( timeout timeout_ms = 0 )

Blocks until at least one entry is available on the queue, then returns the last entry in the queue. If a timeout occurs, an exception is thrown. If the timeout is less than or equal to zero, then the call does not timeout until data is available.

Example:: auto data = queue.pop();

Parameters

timeout_ms a timeout value to wait for data to become available on the queue; integers are interpreted as milliseconds; relative date/time values are interpreted literally with a maximum resolution of milliseconds. A negative timeout value causes the call to time out immediately with a QUEUE-TIMEOUT exception if the call would otherwise block. If a positive timeout argument is passed, and no data is available in the timeout period, a "QUEUE-TIMEOUT" exception is thrown. If no value or a value that converts to integer 0 is passed as the argument, then the call does not timeout until data is available on the queue.

Returns: the last entry on the queue

Note: This method throws a "QUEUE-TIMEOUT" exception on timeout, in order to enable the case where NOTHING was pushed on the queue to be differentiated from a timeout

Exceptions

QUEUE-TIMEOUT	The timeout value was exceeded
QUEUE-ERROR	The queue was deleted while at least one thread was blocked on it
QUEUE-TIMEOUT-ERROR	the timeout value must be >= -2147483648 and <= 2147483647 or this exception is thrown

◆ push()

nothing Qore::Thread::Queue::push	(	auto	arg,
		timeout	timeout_ms = `0`
	)

Pushes a value on the end of the queue.

Example:: queue.push(value);

Parameters

arg value to be put on the queue

timeout_ms a timeout value to wait for a free entry to become available on the queue; integers are interpreted as milliseconds; relative date/time values are interpreted literally with a maximum resolution of milliseconds. A negative timeout value causes the call to time out immediately with a QUEUE-TIMEOUT exception if the call would otherwise block. If a positive timeout argument is passed, and the queue has already reached its maximum size and does not go below the maximum size within the timeout period, a "QUEUE-TIMEOUT" exception is thrown. If no value or a value that converts to integer 0 is passed as the argument, then the call does not timeout until a slot becomes available on the queue. Queue slots are only limited if a maximum size is passed to Queue::constructor().

Exceptions

QUEUE-TIMEOUT	The timeout value was exceeded
QUEUE-ERROR	The queue was deleted while at least one thread was blocked on it
QUEUE-TIMEOUT-ERROR	the timeout value must be >= -2147483648 and <= 2147483647 or this exception is thrown

Since: Qore 0.8.4 this method takes a timeout parameter

◆ setError()

Qore::Thread::Queue::setError	(	string	err,
		string	desc
	)

sets an error status on the Queue and clears the Queue; while a Queue object has an error status, any write operations to the queue will fail and cause an exception to be raised with the information provided to this method

Example:: queue.setError("INVALID-OPERATION", "the data queue has been closed");

Parameters

err	the exception error code string
desc	the exception description string

Any threads blocked on this Queue will be woken up immediately and have the given exception thrown

Note: This method does not throw any exceptions, but exceptions could be thrown by in destructors of objects that go out of scope by being removed from the Queue

See also: clearError()

Since: Qore 0.8.12

◆ size()

int Qore::Thread::Queue::size ( )

Returns the number of elements in the Queue.

Code Flags:: CONSTANT

Example:: int size = queue.size();

Returns: the number of elements in the Queue

See also: Queue::max()

Public Member Methods

Detailed Description

Member Function Documentation

◆ clear()

◆ clearError()

◆ constructor()

◆ destructor()

◆ empty()

◆ get()

◆ getReadWaiting()

◆ getWaiting()

◆ getWriteWaiting()

◆ insert()

◆ max()

◆ pop()

◆ push()

◆ setError()

◆ size()