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pthread_setspecific (3)
  • pthread_setspecific (3) ( FreeBSD man: Библиотечные вызовы )
  • >> pthread_setspecific (3) ( POSIX man: Библиотечные вызовы )
  •  

    NAME

    pthread_getspecific, pthread_setspecific - thread-specific data management
     
    

    SYNOPSIS

    #include <pthread.h>

    void *pthread_getspecific(pthread_key_t key);
    int pthread_setspecific(pthread_key_t
    key, const void *value);
     

    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.  

    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.  

    ERRORS

    No errors are returned from pthread_getspecific().

    The pthread_setspecific() function shall fail if:

    ENOMEM
    Insufficient memory exists to associate the value with the key.

    The pthread_setspecific() function may fail if:

    EINVAL
    The key value is invalid.

    These functions shall not return an error code of [EINTR].

    The following sections are informative.  

    EXAMPLES

    None.  

    APPLICATION USAGE

    None.  

    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.  

    FUTURE DIRECTIONS

    None.  

    SEE ALSO

    pthread_key_create() , the Base Definitions volume of IEEE Std 1003.1-2001, <pthread.h>  

    COPYRIGHT

    Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .


     

    Index

    NAME
    SYNOPSIS
    DESCRIPTION
    RETURN VALUE
    ERRORS
    EXAMPLES
    APPLICATION USAGE
    RATIONALE
    FUTURE DIRECTIONS
    SEE ALSO
    COPYRIGHT


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