управление конкретными данными (specific data management)
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_getspecific, pthread_setspecific — thread-specific data
management
Синопсис (Synopsis)
#include <pthread.h>
void *pthread_getspecific(pthread_key_t key);
int pthread_setspecific(pthread_key_t key, const void *value);
Описание (Description)
The pthread_getspecific() function shall return the value
currently bound to the specified key on behalf of the calling
thread.
The pthread_setspecific() function shall associate a thread-
specific value with a key obtained via a previous call to
pthread_key_create(). Different threads may bind different
values to the same key. These values are typically pointers to
blocks of dynamically allocated memory that have been reserved
for use by the calling thread.
The effect of calling pthread_getspecific() or
pthread_setspecific() with a key value not obtained from
pthread_key_create() or after key has been deleted with
pthread_key_delete() is undefined.
Both pthread_getspecific() and pthread_setspecific() may be
called from a thread-specific data destructor function. A call to
pthread_getspecific() for the thread-specific data key being
destroyed shall return the value NULL, unless the value is
changed (after the destructor starts) by a call to
pthread_setspecific(). Calling pthread_setspecific() from a
thread-specific data destructor routine may result either in lost
storage (after at least PTHREAD_DESTRUCTOR_ITERATIONS attempts at
destruction) or in an infinite loop.
Both functions may be implemented as macros.
Возвращаемое значение (Return value)
The pthread_getspecific() function shall return the thread-
specific data value associated with the given key. If no thread-
specific data value is associated with key, then the value NULL
shall be returned.
If successful, the pthread_setspecific() function shall return
zero; otherwise, an error number shall be returned to indicate
the error.
Ошибки (Error)
No errors are returned from pthread_getspecific().
The pthread_setspecific() function shall fail if:
ENOMEM Insufficient memory exists to associate the non-NULL value
with the key.
The pthread_setspecific() function shall not return an error code
of [EINTR].
The following sections are informative.
Примеры (Examples)
None.
Использование в приложениях (Application usage)
None.
Обоснование (Rationale)
Performance and ease-of-use of pthread_getspecific() are critical
for functions that rely on maintaining state in thread-specific
data. Since no errors are required to be detected by it, and
since the only error that could be detected is the use of an
invalid key, the function to pthread_getspecific() has been
designed to favor speed and simplicity over error reporting.
If an implementation detects that the value specified by the key
argument to pthread_setspecific() does not refer to a a key value
obtained from pthread_key_create() or refers to a key that has
been deleted with pthread_key_delete(), it is recommended that
the function should fail and report an [EINVAL] error.
Будущие направления (Future directions)
None.
Смотри также (See also)
pthread_key_create(3p)
The Base Definitions volume of POSIX.1‐2017, pthread.h(0p)
