pthread_rwlock_wrlock - Acquires a read-write lock for
pthread_rwlock_t *rwlock );
DECthreads POSIX 1003.1c Library (libpthread.so)
Address of the read-write lock object to acquire for write
This routine attempts to acquire a read-write lock for
write access. If any thread already has acquired the lock
for write access or read access, the lock is not granted
and the calling thread blocks until it can acquire the
lock. A thread can hold only one lock for write access on
a read-write lock.
Results are undefined if the calling thread holds the
read-write lock (whether for read or write access) at the
time this routine is called.
If the read-write lock object referenced by rwlock is not
initialized, the results of calling this routine are undefined.
If a thread is interrupted (via a Tru64 UNIX signal or an
OpenVMS AST) while waiting for a read-write lock for write
access, upon return from the interrupt routine the thread
resumes waiting for the lock as if it had not been interrupted.
Real-time applications can encounter priority inversion
when using read-write locks. The problem occurs when a
high-priority thread acquires a read-write lock that is
about to be unlocked (that is, posted) by a low-priority
thread, but the low-priority thread is preempted by a
medium-priority thread. This scenario leads to priority
inversion in that a high-priority thread is blocked by
lower-priority threads for an unlimited period of time.
During system design, real-time programmers must take into
account the possibility of priority inversion and can deal
with it in a number of ways, such as by having critical
sections that are guarded by read-write locks execute at a
high priority, so that a thread cannot be preempted while
executing in its critical section.
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
current thread already owns the read-write lock for write
or read access. The value specified by rwlock does not
refer to an initialized read-write lock object.
Functions: pthread_rwlock_init(3), pthread_rwlockattr_init(3), pthread_rwlock_rdlock(3),
Manuals: Guide to DECthreads and Programmer's Guide
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