Semaphore Services

Collaboration diagram for Semaphore Services:

Functions
void	rtdm_sem_init (rtdm_sem_t *sem, unsigned long value)
	Initialise a semaphore. More...
void	rtdm_sem_destroy (rtdm_sem_t *sem)
	Destroy a semaphore. More...
int	rtdm_sem_down (rtdm_sem_t *sem)
	Decrement a semaphore. More...
int	rtdm_sem_timeddown (rtdm_sem_t *sem, nanosecs_rel_t timeout, rtdm_toseq_t *timeout_seq)
	Decrement a semaphore with timeout. More...
void	rtdm_sem_up (rtdm_sem_t *sem)
	Increment a semaphore. More...
int	rtdm_sem_select (rtdm_sem_t *sem, rtdm_selector_t *selector, enum rtdm_selecttype type, unsigned int fd_index)
	Bind a selector to a semaphore. More...

Detailed Description

Function Documentation

rtdm_sem_destroy()

void rtdm_sem_destroy

(

rtdm_sem_t *

sem

)

Destroy a semaphore.

Parameters

[in,out]

sem

Semaphore handle as returned by rtdm_sem_init()

Tags

task-unrestricted, might-switch

References XNRMID, and xnselect_destroy().

rtdm_sem_down()

int rtdm_sem_down

(

rtdm_sem_t *

sem

)

Decrement a semaphore.

This is the light-weight version of rtdm_sem_timeddown(), implying an infinite timeout.

Parameters

[in,out]

sem

Semaphore handle as returned by rtdm_sem_init()

Returns

0 on success, otherwise:

• -EINTR is returned if calling task has been unblock by a signal or explicitly via rtdm_task_unblock().
• -EIDRM is returned if sem has been destroyed.
• -EPERM may be returned if an illegal invocation environment is detected.

Tags

primary-only, might-switch

References rtdm_sem_timeddown().

rtdm_sem_init()

void rtdm_sem_init	(	rtdm_sem_t *	sem,
		unsigned long	value
	)

Initialise a semaphore.

Parameters

[in,out]	sem	Semaphore handle
[in]	value	Initial value of the semaphore

Tags

task-unrestricted

rtdm_sem_select()

int rtdm_sem_select	(	rtdm_sem_t *	sem,
		rtdm_selector_t *	selector,
		enum rtdm_selecttype	type,
		unsigned int	fd_index
	)

Bind a selector to a semaphore.

This functions binds the given selector to the semaphore so that the former is notified when the semaphore state changes. Typically the select binding handler will invoke this service.

Parameters

[in,out]	sem	Semaphore handle as returned by rtdm_sem_init()
[in,out]	selector	Selector as passed to the select binding handler
[in]	type	Type of the bound event as passed to the select binding handler
[in]	fd_index	File descriptor index as passed to the select binding handler

Returns

0 on success, otherwise:

• -ENOMEM is returned if there is insufficient memory to establish the dynamic binding.
• -EINVAL is returned if type or fd_index are invalid.

Tags

task-unrestricted

rtdm_sem_timeddown()

int rtdm_sem_timeddown	(	rtdm_sem_t *	sem,
		nanosecs_rel_t	timeout,
		rtdm_toseq_t *	timeout_seq
	)

Decrement a semaphore with timeout.

This function tries to decrement the given semphore's value if it is positive on entry. If not, the caller is blocked unless non-blocking operation was selected.

Parameters

[in,out]	sem	Semaphore handle as returned by rtdm_sem_init()
[in]	timeout	Relative timeout in nanoseconds, see RTDM_TIMEOUT_xxx for special values
[in,out]	timeout_seq	Handle of a timeout sequence as returned by rtdm_toseq_init() or NULL

Returns

0 on success, otherwise:

• -ETIMEDOUT is returned if the if the request has not been satisfied within the specified amount of time.
• -EWOULDBLOCK is returned if timeout is negative and the semaphore value is currently not positive.
• -EINTR is returned if calling task has been unblock by a signal or explicitly via rtdm_task_unblock().
• -EIDRM is returned if sem has been destroyed.
• -EPERM may be returned if an illegal invocation environment is detected.

Tags

primary-timed, might-switch

Referenced by rtdm_sem_down().

rtdm_sem_up()

void rtdm_sem_up

(

rtdm_sem_t *

sem

)

Increment a semaphore.

This function increments the given semphore's value, waking up a potential waiter which was blocked upon rtdm_sem_down().

Parameters

[in,out]

sem

Semaphore handle as returned by rtdm_sem_init()

Tags

unrestricted, might-switch