NAME

       pthread_getconcurrency, pthread_setconcurrency - get and set the level of concurrency

SYNOPSIS

       #include <pthread.h>

       int pthread_getconcurrency(void);
       int pthread_setconcurrency(int new_level);

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.

       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() had never been called.

       The   pthread_getconcurrency()   function  shall  return  the  value  set  by  a  previous  call  to  the
       pthread_setconcurrency() function. If the pthread_setconcurrency() function was  not  previously  called,
       this function shall return zero to indicate that the implementation is maintaining the concurrency level.

       A  call to pthread_setconcurrency() shall inform the implementation of its desired concurrency level. The
       implementation shall use this as a hint, not a requirement.

       If an implementation does not support multiplexing of user threads on  top  of  several  kernel-scheduled
       entities,  the  pthread_setconcurrency()  and  pthread_getconcurrency() functions are provided for source
       code compatibility but they shall have no effect when called. To maintain  the  function  semantics,  the
       new_level  parameter  is  saved  when  pthread_setconcurrency()  is  called  so that a subsequent call to
       pthread_getconcurrency() shall return the same value.

RETURN VALUE

       If successful, the pthread_setconcurrency() function shall return zero; otherwise, an error number  shall
       be returned to indicate the error.

       The pthread_getconcurrency() function shall always return the concurrency level set by a previous call to
       pthread_setconcurrency().   If   the   pthread_setconcurrency()   function   has   never   been   called,
       pthread_getconcurrency() shall return zero.

ERRORS

       The pthread_setconcurrency() function shall fail if:

       EINVAL The value specified by new_level is negative.

       EAGAIN The value specific by new_level would cause a system resource to be exceeded.

       These functions shall not return an error code of [EINTR].

       The following sections are informative.

EXAMPLES

       None.

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 applications use of these
       functions.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       The Base Definitions volume of IEEE Std 1003.1-2001, <pthread.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
       Standard  for  Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003 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 .