pthread_rwlock_init - Initializes a read-write lock object with attributes specified by a read-write lock attributes object.
DECthreads POSIX 1003.1c Library (libpthread.so)
const pthread_rwlockattr_t *attr);
Address of the read-write lock object to be initialized. Address of the read-write lock attributes object to use to initialize the object rwlock.
This routine initializes a read-write lock object with the attributes specified by the read-write lock attributes object specified in attr. A read-write lock is a synchronization object that serializes access to shared information that needs to be read frequently and written only occasionally. A thread can acquire a read-write lock for shared read access or for exclusive write access.
Upon successful completion of this routine, the read-write lock is initialized and set to the unlocked state. If attr is set to NULL, the default read-write lock attributes are used; the effect is the same as passing the address of a default read-write lock attributes object. Once initialized, the lock can be used any number of times without being reinitialized.
Results of calling this routine are undefined if attr specifies an already initialized read-write lock or if rwlock is used without first being initialized.
If this routine returns unsuccessfully, rwlock is not initialized and the contents of rwlock are undefined.
A read-write lock is a resource of the process, not part of any particular thread. A read-write lock is neither destroyed not unlocked automatically when any thread exits. Because read-write locks are shared, they may be allocated in heap or static memory, but not on a stack.
In cases where default read-write lock attributes are appropriate, use the PTHREAD_RWLOCK_INITIALIZER macro to statically initialize the lock object without calling this routine. The effect is equivalent to dynamic initialization by a call to pthread_rwlock_init with attr specified as NULL, except that no error checks are performed. Statically initialized read-write locks need not be destroyed using pthread_rwlock_destroy.
Use the PTHREAD_RWLOCK_INITIALIZER macro as follows:
pthread_rwlock_t rwlock = PTHREAD_RWLOCK_INITIALIZER
If an error condition occurs, this routine returns an integer value indicating the type of error. Possible return values are as follows: Successful completion. The system lacks the necessary resources to initialize the read-write lock. Insufficient memory exists to initialize the read-write lock. The caller does not have privileges to perform this operation. The implementation has detected an attempt to reinitialize the read-write lock (a previously initialized, but not yet destroyed read-write lock object). The value specified by attr is invalid.
Manuals: Guide to DECthreads and Programmer's Guide