cras::ReverseSemaphore Class Reference

A reverse counting semaphore which can wait until its count is zero. Each acquire() increases this count and each release() decreases it. waitZero() is the function that waits until the internal count is zero. The semaphore can be disabled, which means no new acquire() calls will be accepted. This is useful if you plan to quit. More...

#include <semaphore.hpp>

Public Member Functions
bool	acquire ()
	Acquire the semaphore (increase its count). This method never blocks for long. More...
void	disable ()
	Disable the semaphore. All following acquire() calls will return immediately with false. More...
void	enable ()
	Enable the semaphore. Calling acquire() works normally after this call. More...
size_t	getCount () const
	Get the current number of unreleased acquire()s. More...
bool	isEnabled () const
	Whether the semaphore is enabled or not. More...
void	release ()
	Release the semaphore (decrease its count). More...
	ReverseSemaphore (bool waitZeroAtDestroy=true)
	Create the semaphore (internal count is zero). More...
bool	waitZero ()
	Wait until the internal count reaches zero. More...
	~ReverseSemaphore ()
	Destroys this semaphore. Internally blocks it and waits for zero count. More...

Private Attributes
volatile size_t	count {0}
	The internal count of the semaphore. More...
::std::condition_variable	cv
	Condition variable used for signalling between release() and waitZero(). More...
volatile bool	disabled {false}
	Whether the semaphore is disabled. More...
bool	isDestroying {false}
	True if the destructor has begun. More...
mutable ::std::mutex	mutex
	Mutex protecting cv, count and disabled. More...
bool	waitZeroAtDestroy
	Whether to wait for zero when the object is being destroyed. More...

Detailed Description

A reverse counting semaphore which can wait until its count is zero. Each acquire() increases this count and each release() decreases it. waitZero() is the function that waits until the internal count is zero. The semaphore can be disabled, which means no new acquire() calls will be accepted. This is useful if you plan to quit.

Definition at line 22 of file semaphore.hpp.

Constructor & Destructor Documentation

ReverseSemaphore()

cras::ReverseSemaphore::ReverseSemaphore ( bool  waitZeroAtDestroy = true )

explicit

Create the semaphore (internal count is zero).

Parameters

[in]

waitZeroAtDestroy

Whether the semaphore should waitForZero() when it is destroyed.

~ReverseSemaphore()

cras::ReverseSemaphore::~ReverseSemaphore

(

)

Destroys this semaphore. Internally blocks it and waits for zero count.

Member Function Documentation

acquire()

bool cras::ReverseSemaphore::acquire

(

)

Acquire the semaphore (increase its count). This method never blocks for long.

Returns

Whether acquisition succeeded. It can fail if the semaphore is disabled.

disable()

void cras::ReverseSemaphore::disable

(

)

Disable the semaphore. All following acquire() calls will return immediately with false.

enable()

void cras::ReverseSemaphore::enable

(

)

Enable the semaphore. Calling acquire() works normally after this call.

getCount()

size_t cras::ReverseSemaphore::getCount

(

)

const

Get the current number of unreleased acquire()s.

Note

Do not use this to tell when all acquire()s are released. Use waitZero() for that.

Returns

The number of unreleased acquire()s.

isEnabled()

bool cras::ReverseSemaphore::isEnabled

(

)

const

Whether the semaphore is enabled or not.

release()

void cras::ReverseSemaphore::release

(

)

Release the semaphore (decrease its count).

Note

If the internal count decreases to zero, all outstanding waitZero() calls are notified.

If the internal count should go below 0, an error is printed to stderr and all outstanding waitZero() calls are notified.

release() calls are processed even if the semaphore is disabled.

waitZero()

bool cras::ReverseSemaphore::waitZero

(

)

Wait until the internal count reaches zero.

Returns

Whether the wait succeeded. False can be returned if this semaphore is being destroyed.

Note

It is suggested to call disable() before this method if you call it because some object needs to exit.

Member Data Documentation

count

volatile size_t cras::ReverseSemaphore::count {0}

private

The internal count of the semaphore.

Definition at line 88 of file semaphore.hpp.

cv

::std::condition_variable cras::ReverseSemaphore::cv

private

Condition variable used for signalling between release() and waitZero().

Definition at line 97 of file semaphore.hpp.

disabled

volatile bool cras::ReverseSemaphore::disabled {false}

private

Whether the semaphore is disabled.

Definition at line 91 of file semaphore.hpp.

isDestroying

bool cras::ReverseSemaphore::isDestroying {false}

private

True if the destructor has begun.

Definition at line 85 of file semaphore.hpp.

mutex

mutable ::std::mutex cras::ReverseSemaphore::mutex

private

Mutex protecting cv, count and disabled.

Definition at line 94 of file semaphore.hpp.

waitZeroAtDestroy

bool cras::ReverseSemaphore::waitZeroAtDestroy

private

Whether to wait for zero when the object is being destroyed.

Definition at line 82 of file semaphore.hpp.

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The documentation for this class was generated from the following file:

• semaphore.hpp