Semaphores

The semaphore is the simplest thread synchronization primitive, consisting of a simple counter. More...

Collaboration diagram for Semaphores:

Data Structures
struct	vlc_sem_t
	Semaphore. More...

Functions
void	vlc_sem_init (vlc_sem_t *sem, unsigned count)
	Initializes a semaphore.
int	vlc_sem_post (vlc_sem_t *)
	Increments the value of a semaphore.
void	vlc_sem_wait (vlc_sem_t *)
	Waits on a semaphore.
int	vlc_sem_trywait (vlc_sem_t *sem)
	Tries to decrement a semaphore.
int	vlc_sem_timedwait (vlc_sem_t *sem, vlc_tick_t deadline)
	Waits on a semaphore within a deadline.

Detailed Description

The semaphore is the simplest thread synchronization primitive, consisting of a simple counter.

See also POSIX sem_t .

Function Documentation

vlc_sem_init()

void vlc_sem_init	(	vlc_sem_t *	sem,
		unsigned	count
	)

Initializes a semaphore.

Parameters

sem	a semaphore to initialize
count	initial semaphore value (typically 0)

References vlc_sem_t::value, and vlc_cond_waiter::value.

Referenced by vlc::threads::semaphore::semaphore(), vlc::threads::semaphore::semaphore(), TaskNew(), TsStart(), vlc_getaddrinfo_i11e(), and vlc_mta_acquire().

vlc_sem_post()

int vlc_sem_post

(

vlc_sem_t *

sem

)

Increments the value of a semaphore.

Note

This function is not a cancellation point.

Returns

0 on success, EOVERFLOW in case of integer overflow.

References unlikely, vlc_sem_t::value, and vlc_atomic_notify_one().

Referenced by Interrupt(), MtaMainLoop(), OnParserEnded(), vlc::threads::semaphore::post(), TsStop(), vlc_gai_thread(), vlc_getaddrinfo_notify(), vlc_interrupt_sem(), and vlc_mta_release().

vlc_sem_timedwait()

int vlc_sem_timedwait	(	vlc_sem_t *	sem,
		vlc_tick_t	deadline
	)

Waits on a semaphore within a deadline.

This function waits for the semaphore just like vlc_sem_wait(), but only up to a given deadline.

Parameters

sem	semaphore to wait for
deadline	deadline to wait until

Return values

0	the semaphore was decremented
ETIMEDOUT	the deadline was reached

References likely, vlc_sem_t::value, and vlc_atomic_timedwait().

Referenced by Parse(), and TsRun().

vlc_sem_trywait()

int vlc_sem_trywait

(

vlc_sem_t *

sem

)

Tries to decrement a semaphore.

This function decrements the semaphore if its value is not zero.

Parameters

sem	semaphore to decrement

Return values

0	the semaphore was decremented
EAGAIN	the semaphore was zero and could not be decremented

References vlc_sem_t::value.

Referenced by TsRun().

vlc_sem_wait()

void vlc_sem_wait

(

vlc_sem_t *

sem

)

Waits on a semaphore.

This function atomically waits for the semaphore to become non-zero then decrements it, and returns. If the semaphore is non-zero on entry, it is immediately decremented.

Note

This function may be a point of cancellation.

References likely, vlc_sem_t::value, and vlc_atomic_wait().

Referenced by MtaMainLoop(), Parse(), vlc_getaddrinfo_i11e(), vlc_mta_acquire(), vlc_sem_wait_i11e(), and vlc::threads::semaphore::wait().