pthread_getconcurrency.3t (2010 09)

p
pthread_getconcurrency(3T) pthread_getconcurrency(3T)
(Pthread Library)
NAME
pthread_getconcurrency(), pthread_setconcurrency() - get or set the concurrency level of unbound threads
SYNOPSIS
#include <pthread.h>
int pthread_setconcurrency(
int new_level
);
int pthread_getconcurrency(void);
PARAMETERS
new_level New concurrency level for the unbound threads in the calling process.
DESCRIPTION
The 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 pro-
vided by the system as a result of this function call is unspecified.
If new_level is zero, it will cause the implementation to maintain the concurrency level at its discretion as
if
pthread_setconcurrency()
were never called.
The
pthread_getconcurrency()
function returns the value set by a previous call to
pthread_setconcurrency()
. If the pthread_setconcurrency()
function was not previously
called, this function returns zero to indicate that the system is maintaining the concurrency level.
Note: When an application calls
pthread_setconcurrency()
, it is informing the implementation of
its desired concurrency level. The implementation will use this as a hint, not a requirement. A call to
pthread_getconcurrency()
immediately after a call to pthread_setconcurrency()
may
return a different concurrency level specified in
pthread_setconcurrency()
.
If the system does not support the multiplexing of user threads on top of several kernel-scheduled enti-
ties, the functions
pthread_getconcurrency()
and pthread_setconcurrency()
functions
will be provided for source code compatibility, but they shall have no effect when called. To maintain the
function semantics, the new_level parameter will be saved when
pthread_setconcurrency()
is
called so that a subsequent call to
pthread_getconcurrency()
will return the same value.
RETURN VALUE
If successful,
pthread_setconcurrency()
returns zero. Otherwise, an error number is returned to
indicate the error (the
errno variable is not set).
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() shall return zero.
ERRORS
If any of the following occur, the
pthread_setconcurrency() function shall return the correspond-
ing error number.
[EINVAL] The value specified by new_level is invalid.
[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 level upon which the application
depends. Library developers are advised to not use the
pthread_getconcurrency() and
pthread_setconcurrency() functions as their use may conflict with an applications use of these
functions.
AUTHOR
pthread_getconcurrency() and pthread_setconcurrency() were developed by X/Open.
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1