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All Rights Reserved. .\" Copyright (c) 2008, Sun Microsystems, Inc. All Rights Reserved. .\" .TH PTHREAD_GETCONCURRENCY 3C "Mar 23, 2005" .SH NAME pthread_getconcurrency, pthread_setconcurrency \- get or set level of concurrency .SH SYNOPSIS .LP .nf cc -mt [ \fIflag\fR... ] \fIfile\fR... -lpthread [ \fIlibrary\fR... ] #include \fBint\fR \fBpthread_getconcurrency\fR(\fBvoid\fR); .fi .LP .nf \fBint\fR \fBpthread_setconcurrency\fR(\fBint\fR \fInew_level\fR); .fi .SH DESCRIPTION .sp .LP 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. .sp .LP The \fBpthread_setconcurrency()\fR function allows an application to inform the threads implementation of its desired concurrency level, \fInew_level\fR. The actual level of concurrency provided by the implementation as a result of this function call is unspecified. .sp .LP If \fInew_level\fR is \fB0\fR, it causes the implementation to maintain the concurrency level at its discretion as if \fBpthread_setconcurrency()\fR was never called. .sp .LP The \fBpthread_getconcurrency()\fR function returns the value set by a previous call to the \fBpthread_setconcurrency()\fR function. If the \fBpthread_setconcurrency()\fR function was not previously called, this function returns \fB0\fR to indicate that the implementation is maintaining the concurrency level. .sp .LP When an application calls \fBpthread_setconcurrency()\fR it is informing the implementation of its desired concurrency level. The implementation uses this as a hint, not a requirement. .sp .LP If an implementation does not support multiplexing of user threads on top of several kernel scheduled entities, the \fBpthread_setconcurrency()\fR and \fBpthread_getconcurrency()\fR functions will be provided for source code compatibility but they will have no effect when called. To maintain the function semantics, the \fInew_level\fR parameter will be saved when \fBpthread_setconcurrency()\fR is called so that a subsequent call to \fBpthread_getconcurrency()\fR returns the same value. .SH RETURN VALUES .sp .LP If successful, the \fBpthread_setconcurrency()\fR function returns \fB0\fR. Otherwise, an error number is returned to indicate the error. .sp .LP The \fBpthread_getconcurrency()\fR function always returns the concurrency level set by a previous call to \fBpthread_setconcurrency()\fR. If the \fBpthread_setconcurrency()\fR function has never been called, \fBpthread_getconcurrency()\fR returns \fB0\fR. .SH ERRORS .sp .LP The \fBpthread_setconcurrency()\fR function will fail if: .sp .ne 2 .na \fB\fBEINVAL\fR\fR .ad .RS 10n The value specified by \fInew_level\fR is negative. .RE .sp .ne 2 .na \fB\fBEAGAIN\fR\fR .ad .RS 10n The value specific by \fInew_level\fR would cause a system resource to be exceeded. .RE .SH ATTRIBUTES .sp .LP See \fBattributes\fR(5) for descriptions of the following attributes: .sp .sp .TS box; c | c l | l . ATTRIBUTE TYPE ATTRIBUTE VALUE _ Interface Stability Standard _ MT-Level MT-Safe .TE .SH SEE ALSO .sp .LP \fBpthread_create\fR(3C), \fBpthread_attr_init\fR(3C), \fBattributes\fR(5), \fBstandards\fR(5)