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

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

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

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