HP-UX Reference (11i v1 00/12) - 3 Library Functions N-Z (vol 7)

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pthread_getconcurrency(3T) pthread_getconcurrency(3T)

(Pthread Library)

NAME

pthread_setconcurrency(), pthread_getconcurrency() - set or get 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 con-

tinue 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 maintainingthe 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 entities,

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.

Section 3−−676 − 1 − HP-UX Release 11i: December 2000

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