получить и установить уровень параллелизма (get and set the level of concurrency)
Пролог (Prolog)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
Имя (Name)
pthread_getconcurrency, pthread_setconcurrency — get and set the
level of concurrency
Синопсис (Synopsis)
#include <pthread.h>
int pthread_getconcurrency(void);
int pthread_setconcurrency(int new_level);
Описание (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.
Возвращаемое значение (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.
Ошибки (Error)
The pthread_setconcurrency() function shall 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.
The pthread_setconcurrency() function shall not return an error
code of [EINTR].
The following sections are informative.
Примеры (Examples)
None.
Использование в приложениях (Application usage)
Application developers should note that an implementation can
always ignore any calls to pthread_setconcurrency() and return a
constant for pthread_getconcurrency(). For this reason, it is
not recommended that portable applications use this function.
Обоснование (Rationale)
None.
Будущие направления (Future directions)
These functions may be removed in a future version.
Смотри также (See also)
The Base Definitions volume of POSIX.1‐2017, pthread.h(0p)
