Detailed Description

Files
file	semaphore.h
	Semaphores.

Macros
#define	SEM_FAILED ((sem_t *) 0)
	Value returned if ‘sem_open’ failed.

Typedefs
typedef sema_t	sem_t
	POSIX-specific semaphore type.

Functions
static int	sem_init (sem_t *sem, int pshared, unsigned value)
	Initialize an unnamed semaphore. More...

static int	sem_destroy (sem_t *sem)
	destroy an unnamed semaphore More...

static int	sem_post (sem_t *sem)
	Unlock a semaphore. More...

static int	sem_wait (sem_t *sem)
	Lock a semaphore. More...

static sem_t *	sem_open (const char *name, int oflag,...)
	Open a named semaphore `name` with open flags `oflag`. More...

static int	sem_close (sem_t *sem)
	Close descriptor for named semaphore `sem`. More...

static int	sem_unlink (const char *name)
	Remove named semaphore `name`. More...

int	sem_timedwait (sem_t sem, const struct timespec abstime)
	Similar to ‘sem_wait’ but wait only until `abstime`. More...

static int	sem_trywait (sem_t *sem)
	Test whether `sem` is posted. More...

static int	sem_getvalue (sem_t sem, int sval)
	Get current value of `sem` and store it in `sval`. More...

Function Documentation

◆ sem_close()

static int sem_close ( sem_t * sem )

inlinestatic

Close descriptor for named semaphore sem.

See also: The Open Group Base Specifications Issue 7, sem_close()

Todo:: named semaphore are currently not supported

Parameters

[in] sem Semaphore to close.

Returns: Always -1, since it is not implemented currently.

Definition at line 198 of file semaphore.h.

◆ sem_destroy()

static int sem_destroy ( sem_t * sem )

inlinestatic

destroy an unnamed semaphore

See also: The Open Group Base Specifications Issue 7, sem_destroy()

The sem_destroy() function shall destroy the unnamed semaphore indicated by sem. Only a semaphore that was created using sem_init() may be destroyed using sem_destroy(); the effect of calling sem_destroy() with a named semaphore is undefined. The effect of subsequent use of the semaphore sem is undefined until sem is reinitialized by another call to sem_init().

It is safe to destroy an initialized semaphore upon which no threads are currently blocked. The effect of destroying a semaphore upon which other threads are currently blocked is undefined.

Parameters

sem	A semaphore.

Returns: 0 on success.; -1, on error and errno set to indicate the error.

Definition at line 96 of file semaphore.h.

◆ sem_getvalue()

static int sem_getvalue	(	sem_t *	sem,
		int *	sval
	)

inlinestatic

Get current value of sem and store it in sval.

See also: The Open Group Base Specifications Issue 7, sem_getvalue()

Parameters

[in]	sem	Semaphore to get the value from.
[out]	sval	Place where value goes to.

Returns: 0 on success.; -1, on error and errno set to indicate the error.

Definition at line 283 of file semaphore.h.

◆ sem_init()

static int sem_init	(	sem_t *	sem,
		int	pshared,
		unsigned	value
	)

inlinestatic

Initialize an unnamed semaphore.

See also: The Open Group Base Specifications Issue 7, sem_init()

The sem_init() function shall initialize the unnamed semaphore referred to by sem. The value of the initialized semaphore shall be value. Following a successful call to sem_init(), the semaphore may be used in subsequent calls to sem_wait(), sem_timedwait(), sem_trywait(), sem_post(), and sem_destroy(). This semaphore shall remain usable until the semaphore is destroyed.

Parameters

[out]	sem	Semaphore to initialize.
[in]	pshared	(unused, since RIOT only has threads) Semaphore is shared between processes not threads.
[in]	value	Value to set.

Returns: 0 on success.; -1, on error and errno set to indicate the error.

Definition at line 68 of file semaphore.h.

◆ sem_open()

static sem_t* sem_open	(	const char *	name,
		int	oflag,
			...
	)

inlinestatic

Open a named semaphore name with open flags oflag.

See also: The Open Group Base Specifications Issue 7, sem_open()

Todo:: named semaphore are currently not supported

Parameters

[in]	name	Name to set.
[in]	oflag	Flags to set.

Returns: Always SEM_FAILED, since it is not implemented currently.

Definition at line 177 of file semaphore.h.

◆ sem_post()

static int sem_post ( sem_t * sem )

inlinestatic

Unlock a semaphore.

See also: The Open Group Base Specifications Issue 7, sem_post()

The sem_post() function shall unlock the semaphore referenced by sem by performing a semaphore unlock operation on that semaphore.

If the semaphore value resulting from this operation is positive, then no threads were blocked waiting for the semaphore to become unlocked; the semaphore value is simply incremented.

If the value of the semaphore resulting from this operation is zero, then one of the threads blocked waiting for the semaphore shall be allowed to return successfully from its call to sem_wait().

Parameters

sem	A semaphore

Returns: 0 on success.; -1, on error and errno set to indicate the error.

Definition at line 124 of file semaphore.h.

◆ sem_timedwait()

int sem_timedwait	(	sem_t *	sem,
		const struct timespec *	abstime
	)

Similar to ‘sem_wait’ but wait only until abstime.

See also: The Open Group Base Specifications Issue 7, sem_timedwait()

The sem_timedwait() function shall lock the semaphore referenced by sem as in the sem_wait() function. However, if the semaphore cannot be locked without waiting for another process or thread to unlock the semaphore by performing a sem_post() function, this wait shall be terminated when the specified timeout expires.

Parameters

[in]	sem	Semaphore to wait on.
[in]	abstime	Absolute time (that is when the clock on which temouts are based equals this value) the timeout for the wait shall expire. If the value specified has already passed the timeout expires immediately.

Returns: 0 on success.; -1, on error and errno set to indicate the error.

◆ sem_trywait()

static int sem_trywait ( sem_t * sem )

inlinestatic

Test whether sem is posted.

See also: The Open Group Base Specifications Issue 7, sem_trywait()

Parameters

[in] sem Semaphore to try to wait on

Returns: 0 on success.; -1, on error and errno set to indicate the error.

Definition at line 259 of file semaphore.h.

◆ sem_unlink()

static int sem_unlink ( const char * name )

inlinestatic

Remove named semaphore name.

See also: The Open Group Base Specifications Issue 7, sem_unlink()

Todo:: named semaphore are currently not supported

Parameters

[in] name Name to unlink.

Returns: Always -1, since it is not implemented currently.

Definition at line 218 of file semaphore.h.

◆ sem_wait()

static int sem_wait ( sem_t * sem )

inlinestatic

Lock a semaphore.

See also: The Open Group Base Specifications Issue 7, sem_wait()

The sem_wait() function shall lock the semaphore referenced by sem by performing a semaphore lock operation on that semaphore. If the semaphore value is currently zero, then the calling thread shall not return from the call to sem_wait() until it either locks the semaphore or the call is interrupted by a signal.

Parameters

sem	A semaphore.

Returns: 0 on success.; -1, on error and errno set to indicate the error.

Definition at line 152 of file semaphore.h.

Detailed Description

Files

Macros

Typedefs

Functions

Function Documentation

◆ sem_close()

◆ sem_destroy()

◆ sem_getvalue()

◆ sem_init()

◆ sem_open()

◆ sem_post()

◆ sem_timedwait()

◆ sem_trywait()

◆ sem_unlink()

◆ sem_wait()