pthread_mutex_init.3t (2010 09)

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pthread_mutex_init(3T) pthread_mutex_init(3T)
(Pthread Library)
NAME
pthread_mutex_init(), pthread_mutex_destroy() - initialize or destroy a mutex
SYNOPSIS
#include <pthread.h>
int pthread_mutex_init(
pthread_mutex_t *__restrict mutex,
const pthread_mutexattr_t *__restrict attr
);
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
int pthread_mutex_destroy(
pthread_mutex_t *mutex
);
PARAMETERS
mutex Pointer to the mutex to be initialized or destroyed.
attr Pointer to the attributes object that defines the characteristics of the mutex to be initial-
ized. If the pointer is NULL, default attributes are used.
DESCRIPTION
The pthread_mutex_init()
function initializes the mutex referenced by mutex with the attributes
attr . If the parameter attr is NULL, the default mutex attributes are used. See
pthread_mutexattr_init(3T) for a list of default mutex attributes. After successful initialization, the
mutex is initialized, unlocked, and ready to be used in mutex operations. A mutex should be initialized
only once or the resulting behavior is undefined. The
pthread_once()
function provides a way to
ensure that a mutex is initialized only once.
The macro
PTHREAD_MUTEX_INITIALIZER
can be used to initialize mutexes that are statically allo-
cated. These mutexes will be initialized with default attributes. The
pthread_mutex_init()
func-
tion does not need to be called for statically initialized mutexes.
If the process-shared attribute in the mutex attributes object referenced by attr is defined as
PTHREAD_PROCESS_SHARED
, the mutex must be allocated such that the processes sharing the mutex
have access to it. This may be done through the memory-mapping functions (see mmap(2)) or the shared
memory functions (see shmget (2)).
The
pthread_mutex_destroy()
function destroys the mutex referenced by mutex. This function
may set mutex to an invalid value. The destroyed mutex can be reinitialized using the function
pthread_mutex_init()
. If the mutex is used after destruction in any mutex call, the resulting
behavior is undefined.
A mutex should be destroyed only when it is unlocked. Destroying a mutex that is currently being used
results in undefined behavior.
RETURN VALUE
Upon successful completion,
pthread_mutex_init() and pthread_mutex_destroy()
return
zero. Otherwise, an error number is returned to indicate the error (the
errno variable is not set).
ERRORS
If any of the following occur, the
pthread_mutex_init() function returns the corresponding error
number:
[EAGAIN] The necessary resources (other than memory) to initialize mutex were not available.
[EBUSY] mutex is an already initialized mutex. However, getting [EBUSY] for reinitializing
the mutex cannot be expected all the time since the behavior of reinitializing the
mutex is undefined.
[EFAULT] mutex points to an illegal address.
[EINVAL] The value specified by mutex or attr is invalid.
[ENOMEM] There is insufficient memory available in which to initialize mutex .
[EPERM] The caller does not have the necessary permission to perform the mutex initializa-
tion.
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