Open System Services System Calls Reference Manual (G06.25+, H06.03+)

ManualsBrandsHP ManualsServerHP NonStop G-Series

301

302

303

304

305

306

307

308

309

310

pthread_once(2) OSS System Calls Reference Manual

NAME

pthread_once - Calls a routine to be executed once by a single thread

LIBRARY

G-series native OSS processes: /G/system/sysnn/zsptsrl

H-series OSS processes: /G/system/zdllnnn/zsptdll

SYNOPSIS

#include <spthread.h>

pthread_once_t once_control = PTHREAD_ONCE_INIT;

int pthread_once(

pthread_once_t *once_control,

void ( *routine)(void) );

PARAMETERS

once_control speciﬁes a block that controls the one-time execution code. Each one-time exe-

cution routine must have its own unique pthread_once_t block.

routine speciﬁes the address of the routine to be executed once. This routine is called

only once, regardless of the number of times it and its associated once_control

block are passed to pthread_once().

DESCRIPTION

The ﬁrst call to this function by any thread in a process with a given once_control block calls the

routine speciﬁed by routine with no arguments. Subsequent calls to pthread_once() with the

same once_control block do not call the routine. On return from pthread_once(), the routine is

guaranteed to have ﬁnished.

For example, a mutex or a per-thread context key must be created exactly once. Calling

pthread_once() ensures that the initialization is serialized across multiple threads. Other

threads that reach the same point in the code are delayed until the ﬁrst thread is ﬁnished.

To initialize the once_control block, use the PTHREAD_ONCE_INIT macro, as shown in the

SYNOPSIS.

RETURN VALUES

If an error condition occurs, this function returns an integer value indicating the type of error.

Possible return values are:

0 Successful completion.

[EINVAL] The value speciﬁed for the once_control parameter is not valid.

STANDARDS CONFORMANCE

This function is an extension to the XPG4 Version 2 speciﬁcation. Interfaces documented on this

reference page conform to the following industry standards:

• IEEE Std 1003.1c-1995, POSIX System Application Program Interface

The use of the header ﬁle spthread.h is an HP exception to the POSIX standard.

5−88 Hewlett-Packard Company 527186-003