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.TH PTHREAD_GETCONCURRENCY "3P" 2013 "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_getconcurrency,

pthread_setconcurrency

\(em get and set the level of concurrency

.SH SYNOPSIS

.LP

.nf

#include <pthread.h>

.P

int pthread_getconcurrency(void);

int pthread_setconcurrency(int \fInew_level\fP);

.fi

.SH DESCRIPTION

Unbound threads in a process may or may not be required to be

simultaneously active. By default, the threads implementation ensures

that a sufficient number of threads are active so that the process can

continue to make progress. While this conserves system resources, it

may not produce the most effective level of concurrency.

.P

The

\fIpthread_setconcurrency\fR()

function allows an application to inform the threads implementation of

its desired concurrency level,

.IR new_level .

The actual level of concurrency provided by the implementation as a

result of this function call is unspecified.

.P

If

.IR new_level

is zero, it causes the implementation to maintain the concurrency level

at its discretion as if

\fIpthread_setconcurrency\fR()

had never been called.

.P

The

\fIpthread_getconcurrency\fR()

function shall return the value set by a previous call to the

\fIpthread_setconcurrency\fR()

function. If the

\fIpthread_setconcurrency\fR()

function was not previously called, this function shall return zero to

indicate that the implementation is maintaining the concurrency level.

.P

A call to

\fIpthread_setconcurrency\fR()

shall inform the implementation of its desired concurrency level.

The implementation shall use this as a hint, not a requirement.

.P

If an implementation does not support multiplexing of user threads on

top of several kernel-scheduled entities, the

\fIpthread_setconcurrency\fR()

and

\fIpthread_getconcurrency\fR()

functions are provided for source code compatibility but they shall

have no effect when called. To maintain the function semantics, the

.IR new_level

parameter is saved when

\fIpthread_setconcurrency\fR()

is called so that a subsequent call to

\fIpthread_getconcurrency\fR()

shall return the same value.

.SH "RETURN VALUE"

If successful, the

\fIpthread_setconcurrency\fR()

function shall return zero; otherwise, an error number shall be

returned to indicate the error.

.P

The

\fIpthread_getconcurrency\fR()

function shall always return the concurrency level set by a previous

call to

\fIpthread_setconcurrency\fR().

If the

\fIpthread_setconcurrency\fR()

function has never been called,

\fIpthread_getconcurrency\fR()

shall return zero.

.SH ERRORS

The

\fIpthread_setconcurrency\fR()

function shall fail if:

.TP

.BR EINVAL

The value specified by

.IR new_level

is negative.

.TP

.BR EAGAIN

The value specified by

.IR new_level

would cause a system resource to be exceeded.

.P

The

\fIpthread_setconcurrency\fR()

function shall not return an error code of

.BR [EINTR] .

.LP

.IR "The following sections are informative."

.SH EXAMPLES

None.

.SH "APPLICATION USAGE"

Application developers should note that an implementation can always

ignore any calls to

\fIpthread_setconcurrency\fR()

and return a constant for

\fIpthread_getconcurrency\fR().

For this reason, it is not recommended that portable applications

use this function.

.SH RATIONALE

None.

.SH "FUTURE DIRECTIONS"

These functions may be removed in a future version.

.SH "SEE ALSO"

The Base Definitions volume of POSIX.1\(hy2008,

.IR "\fB<pthread.h>\fP"

.SH COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form

from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology

-- Portable Operating System Interface (POSIX), The Open Group Base

Specifications Issue 7, Copyright (C) 2013 by the Institute of

Electrical and Electronics Engineers, Inc and The Open Group.

(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .

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 .