call_once, once_flag, ONCE_FLAG_INIT

 

C

Language

headers

Type support

Dynamic memory management

Error handling

Program utilities

Variadic function support

Date and time utilities

Strings library

Algorithms

Numerics

Input/output support

Localization support

Thread support (C11)

Atomic operations (C11)

Technical Specifications

 

Thread support library

Threads
thrd_create thrd_equal thrd_current thrd_sleep thrd_yield thrd_exit	thrd_detach thrd_join thrd_successthrd_timedoutthrd_busythrd_nomemthrd_error
Mutual exclusion
mtx_init mtx_lock mtx_timedlock mtx_trylock call_once	mtx_unlock mtx_destroy mtx_plainmtx_recursivemtx_timed
Condition variables
cnd_init cnd_signal cnd_broadcast	cnd_wait cnd_timedwait cnd_destroy
Thread-local storage
thread_local TSS_DTOR_ITERATIONS tss_create	tss_get tss_set tss_delete

 

Defined in header <threads.h>
void call_once( once_flag* flag, void (*func)(void) );	(1)	(since C11)
typedef /* unspecified */ once_flag	(2)	(since C11)
#define ONCE_FLAG_INIT /* unspecified */	(3)	(since C11)

1) Calls function func exactly once, even if invoked from several threads. The completion of the function func synchronizes with all previous or subsequent calls to call_once with the same flag variable.

2) Complete object type capable of holding a flag used by call_once

3) Expands to a value that can be used to initialize an object of type once_flag.

Parameters

flag	-	pointer to an object of type call_once that is used to ensure func is called only once
func	-	the function to execute only once

Return value

(none)

Notes

The POSIX equivalent of this function is pthread_once.