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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-15 19:43:11 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-15 19:43:11 +0000 |
commit | fc22b3d6507c6745911b9dfcc68f1e665ae13dbc (patch) | |
tree | ce1e3bce06471410239a6f41282e328770aa404a /upstream/archlinux/man3p/pthread_once.3p | |
parent | Initial commit. (diff) | |
download | manpages-l10n-fc22b3d6507c6745911b9dfcc68f1e665ae13dbc.tar.xz manpages-l10n-fc22b3d6507c6745911b9dfcc68f1e665ae13dbc.zip |
Adding upstream version 4.22.0.upstream/4.22.0
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'upstream/archlinux/man3p/pthread_once.3p')
-rw-r--r-- | upstream/archlinux/man3p/pthread_once.3p | 197 |
1 files changed, 197 insertions, 0 deletions
diff --git a/upstream/archlinux/man3p/pthread_once.3p b/upstream/archlinux/man3p/pthread_once.3p new file mode 100644 index 00000000..c9007ef8 --- /dev/null +++ b/upstream/archlinux/man3p/pthread_once.3p @@ -0,0 +1,197 @@ +'\" et +.TH PTHREAD_ONCE "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual" +.\" +.SH PROLOG +This manual page is part of the POSIX Programmer's Manual. +The Linux implementation of this interface may differ (consult +the corresponding Linux manual page for details of Linux behavior), +or the interface may not be implemented on Linux. +.\" +.SH NAME +pthread_once +\(em dynamic package initialization +.SH SYNOPSIS +.LP +.nf +#include <pthread.h> +.P +int pthread_once(pthread_once_t *\fIonce_control\fP, + void (*\fIinit_routine\fP)(void)); +pthread_once_t \fIonce_control\fP = PTHREAD_ONCE_INIT; +.fi +.SH DESCRIPTION +The first call to +\fIpthread_once\fR() +by any thread in a process, with a given +.IR once_control , +shall call the +.IR init_routine +with no arguments. Subsequent calls of +\fIpthread_once\fR() +with the same +.IR once_control +shall not call the +.IR init_routine . +On return from +\fIpthread_once\fR(), +.IR init_routine +shall have completed. The +.IR once_control +parameter shall determine whether the associated initialization +routine has been called. +.P +The +\fIpthread_once\fR() +function is not a cancellation point. However, if +.IR init_routine +is a cancellation point and is canceled, the effect on +.IR once_control +shall be as if +\fIpthread_once\fR() +was never called. +.P +If the call to +.IR init_routine +is terminated by a call to +\fIlongjmp\fR(), +\fI_longjmp\fR(), +or +\fIsiglongjmp\fR(), +the behavior is undefined. +.P +The constant PTHREAD_ONCE_INIT is defined in the +.IR <pthread.h> +header. +.P +The behavior of +\fIpthread_once\fR() +is undefined if +.IR once_control +has automatic storage duration or is not initialized by +PTHREAD_ONCE_INIT. +.SH "RETURN VALUE" +Upon successful completion, +\fIpthread_once\fR() +shall return zero; otherwise, an error number shall be returned to +indicate the error. +.SH ERRORS +The +\fIpthread_once\fR() +function shall not return an error code of +.BR [EINTR] . +.LP +.IR "The following sections are informative." +.SH EXAMPLES +None. +.SH "APPLICATION USAGE" +If +.IR init_routine +recursively calls +\fIpthread_once\fR() +with the same +.IR once_control , +the recursive call will not call the specified +.IR init_routine , +and thus the specified +.IR init_routine +will not complete, and thus the recursive call to +\fIpthread_once\fR() +will not return. Use of +\fIlongjmp\fR(), +\fI_longjmp\fR(), +or +\fIsiglongjmp\fR() +within an +.IR init_routine +to jump to a point outside of +.IR init_routine +prevents +.IR init_routine +from returning. +.SH RATIONALE +Some C libraries are designed for dynamic initialization. That is, the +global initialization for the library is performed when the first +procedure in the library is called. In a single-threaded program, this +is normally implemented using a static variable whose value is checked +on entry to a routine, as follows: +.sp +.RS 4 +.nf + +static int random_is_initialized = 0; +extern void initialize_random(void); +.P +int random_function() +{ + if (random_is_initialized == 0) { + initialize_random(); + random_is_initialized = 1; + } + ... /* Operations performed after initialization. */ +} +.fi +.P +.RE +.P +To keep the same structure in a multi-threaded program, a new primitive +is needed. Otherwise, library initialization has to be accomplished by +an explicit call to a library-exported initialization function prior to +any use of the library. +.P +For dynamic library initialization in a multi-threaded process, if an +initialization flag is used the flag needs to be protected against +modification by multiple threads simultaneously calling into the +library. This can be done by using a mutex (initialized by assigning +PTHREAD_MUTEX_INITIALIZER). However, the better solution is to use +\fIpthread_once\fR() +which is designed for exactly this purpose, as follows: +.sp +.RS 4 +.nf + +#include <pthread.h> +static pthread_once_t random_is_initialized = PTHREAD_ONCE_INIT; +extern void initialize_random(void); +.P +int random_function() +{ + (void) pthread_once(&random_is_initialized, initialize_random); + ... /* Operations performed after initialization. */ +} +.fi +.P +.RE +.P +If an implementation detects that the value specified by the +.IR once_control +argument to +\fIpthread_once\fR() +does not refer to a +.BR pthread_once_t +object initialized by PTHREAD_ONCE_INIT, it is recommended that the +function should fail and report an +.BR [EINVAL] +error. +.SH "FUTURE DIRECTIONS" +None. +.SH "SEE ALSO" +The Base Definitions volume of POSIX.1\(hy2017, +.IR "\fB<pthread.h>\fP" +.\" +.SH COPYRIGHT +Portions of this text are reprinted and reproduced in electronic form +from IEEE Std 1003.1-2017, Standard for Information Technology +-- Portable Operating System Interface (POSIX), The Open Group Base +Specifications Issue 7, 2018 Edition, +Copyright (C) 2018 by the Institute of +Electrical and Electronics Engineers, Inc and The Open Group. +In the event of any discrepancy between this version and the original IEEE and +The Open Group Standard, the original IEEE and The Open Group Standard +is the referee document. The original Standard can be obtained online at +http://www.opengroup.org/unix/online.html . +.PP +Any typographical or formatting errors that appear +in this page are most likely +to have been introduced during the conversion of the source files to +man page format. To report such errors, see +https://www.kernel.org/doc/man-pages/reporting_bugs.html . |