pthread_rwlock_init.3t (2010 09)

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pthread_rwlock_init(3T) pthread_rwlock_init(3T)
(Pthread Library)
NAME
pthread_rwlock_init(), pthread_rwlock_destroy() - initialize or destroy a read-write lock
SYNOPSIS
#include <pthread.h>
int pthread_rwlock_init(
pthread_rwlock_t *__restrict rwlock,
const pthread_rwlockattr_t *__restrict attr
);
pthread_rwlock_t rwlock = PTHREAD_RWLOCK_INITIALIZER;
int pthread_rwlock_destroy(
pthread_rwlock_t *rwlock
);
PARAMETERS
rwlock Pointer to the read-write lock to be initialized or destroyed.
attr Pointer to the attributes object that defines the characteristics of the read-write lock to be
initialized. If the pointer is NULL, default attributes are used.
DESCRIPTION
pthread_rwlock_init()
initializes the read-write lock referenced by rwlock with the attributes
attr .Ifattr is NULL, the default read-write lock attributes are used. Upon successful initialization, the
state of the read-write lock becomes initialized and unlocked. Attempting to initialize an already initial-
ized read-write lock object results in undefined behavior.
The macro
PTHREAD_RWLOCK_INITIALIZER
can be used to initialize read-write locks which are stati-
cally allocated. The effect is equivalent to dynamic initialization by a call to
pthread_rwlock_init()
with the attr parameter specified as NULL, except that no error checks are
performed. The read-write lock will be initialized with default attributes.
If the process-shared attribute in the read-write lock attributes object referenced by attr is defined as
PTHREAD_PROCESS_SHARED
, the read-write lock must be allocated such that the processes sharing the
read-write lock has access to it. This may be done through the memory-mapping functions (see mmap(2))
or shared memory functions (see shmget(2)).
pthread_rwlock_destroy()
destroys the read-write referenced by rwlock . This function may set
rwlock to an invalid value. The destroyed read-write lock can be reinitialized using the function
pthread_rwlock_init()
. If the read-write lock is referenced after destruction in any read-write
lock call, the resulting behavior is undefined.
A read-write lock should be destroyed only when no threads are currently using it. Destroying a read-
write lock which is currently in use results in undefined behavior.
RETURN VALUE
Upon successful completion,
pthread_rwlock_init() and pthread_rwlock_destroy()
returns 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_rwlock_init() function returns the corresponding error
number:
[EAGAIN] The necessary resources (other than memory) to initialize rwlock are not available.
[EBUSY] rwlock is an already initialized read-write lock. However, getting [EBUSY] for
reinitializing the rwlock cannot be expected all the time since the behavior of reini-
tializing the rwlock is undefined.
[EINVAL] The value specified by rwlock or attr is invalid.
[ENOMEM] There is insufficient memory available in which to initialize the read-write lock
rwlock .
[EPERM] The caller does not have the privilege to perform the operation.
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