pthread_rwlock_trywrlock - Attempts to acquire a readwrite
lock for write access without waiting
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 the read-write lock referenced
by rwlock for write access. If any thread already
holds that lock for write access or read access, this routine
fails and returns [EBUSY] and the calling thread does
not wait for the lock to become available.
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.
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
read-write lock could not be acquired for write access
because it was already locked for write access or for read
access. The value specified by rwlock does not refer to
an initialized read-write lock object. The current thread
already owns the read-write lock for write or read access.
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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