NAME

semaphore, sema_init, sema_destroy, sema_p, sema_p_sig, sema_v, sema_tryp − semaphore functions

SYNOPSIS

#include <sys/ksynch.h>

void sema_init(ksema_t ∗sp, u_int val, char ∗name, ksema_type_t type, void ∗arg);

void sema_destroy(ksema_t ∗sp);

void sema_p(ksema_t ∗sp);

void sema_v(ksema_t ∗sp);

int sema_p_sig(ksema_t ∗sp);

int sema_tryp(ksema_t ∗sp);

INTERFACE LEVEL

Solaris DDI specific (Solaris DDI). 

ARGUMENTS

sp A pointer to a semaphore, type ksema_t. 

val Initial value for semaphore. 

name A string describing the semaphore for statistics and debugging. 

type Variant type of the semaphore.  Currently only SEMA_DRIVER is supported. 

arg Type-specific argument, should be NULL.

DESCRIPTION

These functions implement counting semaphores as described by Dijkstra.  A semaphore has a value which is atomicly decremented by sema_p() and atomicly incremented by sema_v().  The value must always be greater than or equal to zero.  If sema_p() is called and the value is zero, the calling thread is blocked until another thread performs a sema_v() operation on the semaphore. 

Semaphores are initialized by calling sema_init().  The argument, val, gives the initial value for the semaphore. The semaphore storage is provided by the caller but more may be dynamicly allocated, if necessary, by sema_init().  For this reason, sema_destroy() should be called before deallocating the storage containing the semaphore. 

sema_p_sig() decrements the semaphore, as does sema_p(), however, if the semaphore value is zero, sema_p_sig() will return without decrementing the value if a signal (e.g. from kill(2)) is pending for the thread. 

sema_tryp() will decrement the semaphore value only if it is greater than zero, and will not block. 

RETURN VALUES

0 sema_tryp() could not decrement the semaphore value because it was zero. 

1 sema_p_sig() was not able to decrement the semaphore value and detected a pending signal. 

CONTEXT

These function can be called from user or interrupt context, except for sema_init() and sema_destroy(), which can be called from user context only. 

SEE ALSO

kill(2), condvar(9F), mutex(9F)

Writing Device Drivers

SunOS 5.4  —  Last change: 17 Oct 1991