A counting semaphore is a generalization of a mutex semaphore that allows multiple resources to be locked and unlocked. Threads can use the blocking method lock() to acquire a single resource, or they can use the method try_lock() to attempt acquisition of one or more resources without blocking.

Unlike the os_mutex_semaphore , an os_counting_semaphore is not owned by a particular thread; it is simply owned. One thread can wait() and a different thread can post() to increase the available resource count and unblock waiters. Contrast this with an os_mutex_semaphore , where the same thread that waits (and acquires the resource) must also post to release the resource.

Interface

Constructor

os_counting_semaphore( unsigned int initial )

Constructs a counting semaphore with initial resources available.

Throws: os_thread_toolkit_error

Constructor

os_counting_semaphore( unsigned int initial , unsigned int maximum )

Constructs a counting semaphore with initial resources available and a maximum size.

Throws: os_thread_toolkit_error

Destructor

~os_counting_semaphore()

Destroys this semaphore.

count

unsigned int count() const

Returns the current count.

Throws: os_thread_toolkit_error

lock

void lock( unsigned int count )

Decrements the number of resources by count (default 1 ). If no resources are present, blocks until one becomes available.

Throws: os_thread_toolkit_error

obtain

void obtain( unsigned int count )

Synonym for lock() ; alternative acquisition syntax.

Throws: os_thread_toolkit_error

post

void post( unsigned int count )

Synonym for unlock() ; alternative event syntax.

Throws: os_thread_toolkit_error

print

void print( ostream& stream ) const

Prints to stream .

Throws: os_thread_toolkit_error

release

void release( unsigned int count )

Synonym for unlock() ; alternative acquisition syntax.

Throws: os_thread_toolkit_error

size

unsigned
    int size() const

Returns size.

Throws: os_thread_toolkit_error

try_lock

bool try_lock( unsigned int count )

If the counting semaphore has at least count resources, decrements the resources by count (default 1 ) and returns true ; otherwise, leaves the resource count unchanged and immediately returns false .

Throws: os_thread_toolkit_error

unlock

void unlock( unsigned int count )

Increments the number of resources by count (default 1 ).

Throws: os_thread_toolkit_error

wait

void wait( unsigned int count )

Synonym for lock() ; alternative event syntax.

Throws: os_thread_toolkit_error

counting_semaphore

Library

Declaration

Typedefs

Interface

Non-Member Functions