pthread_rwlock_init(3)pthread_rwlock_init(3)NAMEpthread_rwlock_init - Initializes a read-write lock object
SYNOPSIS
#include <pthread.h>
int pthread_rwlock_init(
pthread_rwlock_t *rwlock,
const pthread_rwlockattr_t *attr );
LIBRARY
DECthreads POSIX 1003.1c Library (libpthread.so)
PARAMETERS
Read-write lock object to be initialized. Read-write lock attributes
object that defines the characteristics of the read-write lock to be
initialized.
DESCRIPTION
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 ini‐
tialized 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 partic‐
ular thread. A read-write lock is neither destroyed not unlocked auto‐
matically 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, you
may 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. Stati‐
cally 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;
RETURN VALUES
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. 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 not a valid attributes block. Insufficient memory exists to
initialize the read-write lock. The caller does not have privileges to
perform this operation.
ERRORS
None
SEE ALSO
Functions: pthread_rwlock_destroy(3)
Manuals: Guide to DECthreads and Programmer's Guide
pthread_rwlock_init(3)
