pthread_rwlock_rdlock.3 [plain text]
.\" Copyright (c) 1998 Alex Nash
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.\" $FreeBSD: src/lib/libc_r/man/pthread_rwlock_rdlock.3,v 1.4 2001/10/01 16:09:09 ru Exp $
.Dd August 4, 1998
.Dt PTHREAD_RWLOCK_RDLOCK 3
.Nm pthread_rwlock_rdlock ,
.Nd acquire a read/write lock for reading
.Fn pthread_rwlock_rdlock "pthread_rwlock_t *lock"
.Fn pthread_rwlock_tryrdlock "pthread_rwlock_t *lock"
function acquires a read lock on
is not presently held for writing and no writer threads are
presently blocked on the lock. If the read lock cannot be
immediately acquired, the calling thread blocks until it can
acquire the lock.
function performs the same action, but does not block if the lock
cannot be immediately obtained (i.e. the lock is held for writing
or there are waiting writers).
A thread may hold multiple concurrent read locks. If so,
must be called once for each lock obtained.
The results of acquiring a read lock while the calling thread holds
a write lock are undefined.
.Sh IMPLEMENTATION NOTES
To prevent writer starvation, writers are favored over readers.
.Sh RETURN VALUES
If successful, the
functions will return zero. Otherwise an error number will be returned
to indicate the error.
.Sh SEE ALSO
.Xr pthread_rwlock_init 3 ,
.Xr pthread_rwlock_trywrlock 3 ,
.Xr pthread_rwlock_unlock 3 ,
.Xr pthread_rwlock_wrlock 3
functions are expected to conform to
.St -susv2 .
function will fail if:
.Bl -tag -width Er
.It Bq Er EBUSY
The lock could not be acquired because a writer holds the lock or
was blocked on it.
functions may fail if:
.Bl -tag -width Er
.It Bq Er EAGAIN
The lock could not be acquired because the maximum number of read locks
has been exceeded.
.It Bq Er EDEADLK
The current thread already owns
.It Bq Er EINVAL
The value specified by
.It Bq Er ENOMEM
Insufficient memory exists to initialize the lock (applies to
statically initialized locks only).
function first appeared in
.Fx 3.0 .