Standard C Library Functions           pthreadgetconcurrency(3C)



NAME
     pthreadgetconcurrency, pthreadsetconcurrency - get or  set
     level of concurrency

SYNOPSIS
     cc -mt [ flag... ] file... -lpthread [ library... ]
     #include 

     int pthreadgetconcurrency(void);


     int pthreadsetconcurrency(int newlevel);


DESCRIPTION
     Unbound threads in a process may or may not be  required  to
     be  simultaneously active. By default, the threads implemen-
     tation 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  pthreadsetconcurrency() function allows an application
     to  inform  the  threads  implementation of its desired con-
     currency level, newlevel. The actual level  of  concurrency
     provided  by the implementation as a result of this function
     call is unspecified.


     If newlevel is  0, it causes the implementation to maintain
     the    concurrency   level   at   its   discretion   as   if
     pthreadsetconcurrency() was never called.


     The  pthreadgetconcurrency() function  returns  the   value
     set  by  a  previous  call  to the  pthreadsetconcurrency()
     function. If the  pthreadsetconcurrency() function was  not
     previously called, this function returns  0 to indicate that
     the implementation is maintaining the concurrency level.


     When an application calls   pthreadsetconcurrency()  it  is
     informing  the  implementation  of  its  desired concurrency
     level. The  implementation  uses  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
     pthreadsetconcurrency() and  pthreadgetconcurrency() func-
     tions  will  be  provided  for source code compatibility but



SunOS 5.11          Last change: 23 Mar 2005                    1






Standard C Library Functions           pthreadgetconcurrency(3C)



     they will have no effect when called. To maintain the  func-
     tion  semantics,  the newlevel parameter will be saved when
     pthreadsetconcurrency() is called so that a subsequent call
     to pthreadgetconcurrency() returns the same value.

RETURN VALUES
     If  successful,   the    pthreadsetconcurrency()   function
     returns   0. Otherwise, an error number is returned to indi-
     cate the error.


     The  pthreadgetconcurrency() function  always  returns  the
     concurrency    level    set    by   a   previous   call   to
     pthreadsetconcurrency(). If  the   pthreadsetconcurrency()
     function  has  never  been called,  pthreadgetconcurrency()
     returns  0.

ERORS
     The pthreadsetconcurrency() function will fail if:

     EINVAL    The value specified by newlevel is negative.


     EAGAIN    The value specific by newlevel would cause a sys-
               tem resource to be exceeded.


ATRIBUTES
     See attributes(5) for descriptions of the  following  attri-
     butes:



     
           ATRIBUTE TYPE               ATRIBUTE VALUE       
    
     Interface Stability          Standard                    
    
     MT-Level                     MT-Safe                     
    


SEE ALSO
     pthreadcreate(3C),  pthreadattrinit(3C),   attributes(5),
     standards(5)










SunOS 5.11          Last change: 23 Mar 2005                    2