NAME

pthread_getconcurrency, pthread_setconcurrency —

get or set level of concurrency

LIBRARY

POSIX Threads Library (libpthread, -lpthread)

SYNOPSIS

#include <pthread.h>

int
pthread_getconcurrency(void);

int
pthread_setconcurrency(int new_level);

DESCRIPTION

The pthread_setconcurrency() function allows an application to inform the threads implementation of its desired concurrency level, new_level. The actual level of concurrency provided by the implementation as a result of this function call is unspecified. If new_level is zero, it causes the implementation to maintain the concurrency level at its discretion as if pthread_setconcurrency() was never called. The pthread_getconcurrency() function returns the value set by a previous call to the pthread_setconcurrency() function. If the pthread_setconcurrency() function was not previously called, this function returns zero to indicate that the implementation is maintaining the concurrency level. When an application calls pthread_setconcurrency(), it is informing the implementation of its desired concurrency level. The implementation uses this as a hint, not a requirement.

RETURN VALUES

If successful, the pthread_setconcurrency() function returns zero. Otherwise, an error number is returned to indicate the error. The pthread_getconcurrency() function always returns the concurrency level set by a previous call to pthread_setconcurrency(). If the pthread_setconcurrency() function has never been called, pthread_getconcurrency() returns zero.

ERRORS

The pthread_setconcurrency() function will fail if:

[EINVAL]: The value specified by new_level is negative.
[EAGAIN]: The value specified by new_level would cause a system resource to be exceeded.

APPLICATION USAGE

Use of these functions changes the state of the underlying concurrency upon which the application depends. Library developers are advised to not use the pthread_getconcurrency() and pthread_setconcurrency() functions since their use may conflict with an application's use of these functions.

STANDARDS

The pthread_getconcurrency() and pthread_setconcurrency() functions conform to Version 2 of the Single UNIX Specification (“SUSv2”).