PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

PTHREAD_RWLOCK_RDLOCK(3P) POSIX Programmer's ManualPTHREAD_RWLOCK_RDLOCK(3P)

PROLOG         top

       This manual page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior), or
       the interface may not be implemented on Linux.

NAME         top

       pthread_rwlock_rdlock, pthread_rwlock_tryrdlock — lock a read-write
       lock object for reading

SYNOPSIS         top

       #include <pthread.h>

       int pthread_rwlock_rdlock(pthread_rwlock_t *rwlock);
       int pthread_rwlock_tryrdlock(pthread_rwlock_t *rwlock);

DESCRIPTION         top

       The pthread_rwlock_rdlock() function shall apply a read lock to the
       read-write lock referenced by rwlock.  The calling thread acquires
       the read lock if a writer does not hold the lock and there are no
       writers blocked on the lock.

       If the Thread Execution Scheduling option is supported, and the
       threads involved in the lock are executing with the scheduling
       policies SCHED_FIFO or SCHED_RR, the calling thread shall not acquire
       the lock if a writer holds the lock or if writers of higher or equal
       priority are blocked on the lock; otherwise, the calling thread shall
       acquire the lock.

       If the Thread Execution Scheduling option is supported, and the
       threads involved in the lock are executing with the SCHED_SPORADIC
       scheduling policy, the calling thread shall not acquire the lock if a
       writer holds the lock or if writers of higher or equal priority are
       blocked on the lock; otherwise, the calling thread shall acquire the
       lock.

       If the Thread Execution Scheduling option is not supported, it is
       implementation-defined whether the calling thread acquires the lock
       when a writer does not hold the lock and there are writers blocked on
       the lock. If a writer holds the lock, the calling thread shall not
       acquire the read lock. If the read lock is not acquired, the calling
       thread shall block until it can acquire the lock. The calling thread
       may deadlock if at the time the call is made it holds a write lock.

       A thread may hold multiple concurrent read locks on rwlock (that is,
       successfully call the pthread_rwlock_rdlock() function n times). If
       so, the application shall ensure that the thread performs matching
       unlocks (that is, it calls the pthread_rwlock_unlock() function n
       times).

       The maximum number of simultaneous read locks that an implementation
       guarantees can be applied to a read-write lock shall be
       implementation-defined. The pthread_rwlock_rdlock() function may fail
       if this maximum would be exceeded.

       The pthread_rwlock_tryrdlock() function shall apply a read lock as in
       the pthread_rwlock_rdlock() function, with the exception that the
       function shall fail if the equivalent pthread_rwlock_rdlock() call
       would have blocked the calling thread. In no case shall the
       pthread_rwlock_tryrdlock() function ever block; it always either
       acquires the lock or fails and returns immediately.

       Results are undefined if any of these functions are called with an
       uninitialized read-write lock.

       If a signal is delivered to a thread waiting for a read-write lock
       for reading, upon return from the signal handler the thread resumes
       waiting for the read-write lock for reading as if it was not
       interrupted.

RETURN VALUE         top

       If successful, the pthread_rwlock_rdlock() function shall return
       zero; otherwise, an error number shall be returned to indicate the
       error.

       The pthread_rwlock_tryrdlock() function shall return zero if the lock
       for reading on the read-write lock object referenced by rwlock is
       acquired. Otherwise, an error number shall be returned to indicate
       the error.

ERRORS         top

       The pthread_rwlock_tryrdlock() function shall fail if:

       EBUSY  The read-write lock could not be acquired for reading because
              a writer holds the lock or a writer with the appropriate
              priority was blocked on it.

       The pthread_rwlock_rdlock() and pthread_rwlock_tryrdlock() functions
       may fail if:

       EAGAIN The read lock could not be acquired because the maximum number
              of read locks for rwlock has been exceeded.

       The pthread_rwlock_rdlock() function may fail if:

       EDEADLK
              A deadlock condition was detected or the current thread
              already owns the read-write lock for writing.

       These functions shall not return an error code of [EINTR].

       The following sections are informative.

EXAMPLES         top

       None.

APPLICATION USAGE         top

       Applications using these functions may be subject to priority
       inversion, as discussed in the Base Definitions volume of
       POSIX.1‐2008, Section 3.287, Priority Inversion.

RATIONALE         top

       If an implementation detects that the value specified by the rwlock
       argument to pthread_rwlock_rdlock() or pthread_rwlock_tryrdlock()
       does not refer to an initialized read-write lock object, it is
       recommended that the function should fail and report an [EINVAL]
       error.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       pthread_rwlock_destroy(3p), pthread_rwlock_timedrdlock(3p),
       pthread_rwlock_timedwrlock(3p), pthread_rwlock_trywrlock(3p),
       pthread_rwlock_unlock(3p)

       The Base Definitions volume of POSIX.1‐2008, Section 3.287,  Priority
       Inversion, Section 4.11, Memory Synchronization, pthread.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) In the event of any discrepancy between this version and
       the original IEEE and The Open Group Standard, the original IEEE and
       The Open Group Standard is the referee document. The original
       Standard can be obtained online at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the
       source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013           PTHREAD_RWLOCK_RDLOCK(3P)