semaphore.h

Introduction

Use the links in the table of contents to the left to access the documentation.

Functions

dispatch_semaphore_create

Creates new counting semaphore with an initial value.

dispatch_semaphore_signal

Signal (increment) a semaphore.

dispatch_semaphore_wait

Wait (decrement) for a semaphore.

dispatch_semaphore_create

Creates new counting semaphore with an initial value.

(
    macos(
        10.6),
    ios(
        4.0)) DISPATCH_MALLOC DISPATCH_RETURNS_RETAINED   dispatch_semaphore_t dispatch_semaphore_create(
    intptr_t value);  

Parameters

Return Value

The newly created semaphore, or NULL on failure.

Discussion

Passing zero for the value is useful for when two threads need to reconcile the completion of a particular event. Passing a value greater than zero is useful for managing a finite pool of resources, where the pool size is equal to the value.

dispatch_semaphore_signal

Signal (increment) a semaphore.

(
    macos(
        10.6),
    ios(
        4.0))  intptr_t dispatch_semaphore_signal(
    dispatch_semaphore_t dsema);  

Parameters

Return Value

This function returns non-zero if a thread is woken. Otherwise, zero is returned.

Discussion

Increment the counting semaphore. If the previous value was less than zero, this function wakes a waiting thread before returning.

dispatch_semaphore_wait

Wait (decrement) for a semaphore.

(
    macos(
        10.6),
    ios(
        4.0))  intptr_t dispatch_semaphore_wait(
    dispatch_semaphore_t dsema,
    dispatch_time_t timeout);  

Parameters

Return Value

Returns zero on success, or non-zero if the timeout occurred.

Discussion

Decrement the counting semaphore. If the resulting value is less than zero, this function waits for a signal to occur before returning.

Typedefs

dispatch_semaphore_t

A counting semaphore.

dispatch_semaphore_t

A counting semaphore.

typedef struct dispatch_semaphore_s *dispatch_semaphore_t;