Semaphore Usage
[L4 Semaphore API]

L4 Semaphore usage. More...

Defines
#define	L4SEMAPHORE_INITIALIZER(x)   {(x), 0, NULL}
	Semaphore initializer, use this to initialize semaphores in nested structures.
#define	L4SEMAPHORE_INIT(x)   ((l4semaphore_t)L4SEMAPHORE_INITIALIZER(x))
	Semaphore value generator, use this to initialize plain semaphores.
#define	L4SEMAPHORE_LOCKED_INITIALIZER   L4SEMAPHORE_INITIALIZER(0)
	Semaphore initializer, initial count 0 (semaphore locked).
#define	L4SEMAPHORE_LOCKED   ((l4semaphore_t)L4SEMAPHORE_LOCKED_INITIALIZER)
	Locked semaphore value, initial count 0.
#define	L4SEMAPHORE_UNLOCKED_INITIALIZER   L4SEMAPHORE_INITIALIZER(1)
	Semaphore initializer, initial count 1 (semaphore unlocked).
#define	L4SEMAPHORE_UNLOCKED   ((l4semaphore_t)L4SEMAPHORE_UNLOCKED_INITIALIZER)
	Unlocked semaphore value, initial count 1.
Functions
L4_INLINE void	l4semaphore_down (l4semaphore_t *sem)
	Decrement semaphore counter, block if result is < 0.
L4_INLINE int	l4semaphore_down_timed (l4semaphore_t *sem, unsigned timeout)
	Decrement semaphore counter, block for a given time if result is < 0.
L4_INLINE int	l4semaphore_try_down (l4semaphore_t *sem)
	Decrement semaphore counter, do not wait if result is < 0.
L4_INLINE void	l4semaphore_up (l4semaphore_t *sem)
	Increment semaphore counter, wakeup next thread in wait queue.

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Detailed Description

L4 Semaphore usage.

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Define Documentation

#define L4SEMAPHORE_INITIALIZER

(

x

)

{(x), 0, NULL}

Semaphore initializer, use this to initialize semaphores in nested structures.

Parameters:

x

Initial value for semaphore counter

Definition at line 73 of file semaphore.h.

#define L4SEMAPHORE_INIT

(

x

)

((l4semaphore_t)L4SEMAPHORE_INITIALIZER(x))

Semaphore value generator, use this to initialize plain semaphores.

Parameters:

x

Initial value for semaphore counter

Definition at line 80 of file semaphore.h.

#define L4SEMAPHORE_LOCKED_INITIALIZER   L4SEMAPHORE_INITIALIZER(0)

Semaphore initializer, initial count 0 (semaphore locked).

Definition at line 87 of file semaphore.h.

#define L4SEMAPHORE_LOCKED   ((l4semaphore_t)L4SEMAPHORE_LOCKED_INITIALIZER)

Locked semaphore value, initial count 0.

Definition at line 94 of file semaphore.h.

#define L4SEMAPHORE_UNLOCKED_INITIALIZER   L4SEMAPHORE_INITIALIZER(1)

Semaphore initializer, initial count 1 (semaphore unlocked).

Definition at line 101 of file semaphore.h.

#define L4SEMAPHORE_UNLOCKED   ((l4semaphore_t)L4SEMAPHORE_UNLOCKED_INITIALIZER)

Unlocked semaphore value, initial count 1.

Definition at line 108 of file semaphore.h.

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Function Documentation

L4_INLINE void l4semaphore_down

(

l4semaphore_t *

sem

)

Decrement semaphore counter, block if result is < 0.

Parameters:

sem

Semaphore structure

Decrement semaphore counter by 1. If the result is < 0, l4semaphore_down blocks and waits for the release of the semaphore.

L4_INLINE int l4semaphore_down_timed	(	l4semaphore_t *	sem,
		unsigned	timeout
	)

Decrement semaphore counter, block for a given time if result is < 0.

Parameters:

	sem	Semaphore structure
	timeout	Timeout (in ms), timeout must be positive

Returns:

0 if semaphore successfully decremented within given time, != 0 otherwise.

: A timeout of 0 ms means promptly checkin to enter the critical section. If infinitive timeouts are required, use l4semaphore_down instead.

Decrement semaphore counter by 1. If the result is < 0, l4semaphore_down_timed blocks for time ms and waits for the release of the semaphore.

L4_INLINE int l4semaphore_try_down

(

l4semaphore_t *

sem

)

Decrement semaphore counter, do not wait if result is < 0.

Parameters:

sem

Semaphore structure

Returns:

1 on success (counter decremented), 0 if semaphore already locked

Try to decrement semaphore counter by 1, if the result would be < 0, return error instead.

L4_INLINE void l4semaphore_up

(

l4semaphore_t *

sem

)

Increment semaphore counter, wakeup next thread in wait queue.

Parameters:

sem

Semaphore structure

Increment semaphore counter by 1. If threads are enqueued in the wait queue, wakeup the first thread.