pthread_rwlock_rdlock(3p) — Linux manual page

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

PTHREAD_RWLOCK_RDLOCK(3P)OSIX Programmer's ManualHREAD_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.1‐2017, Section 3.291, 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.1‐2017, Section 3.291,
       Priority Inversion, Section 4.12, Memory Synchronization,
       pthread.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  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.opengroup.org/unix/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               2017         PTHREAD_RWLOCK_RDLOCK(3P)

Pages that refer to this page: pthread.h(0p)pthread_rwlock_destroy(3p)pthread_rwlock_timedrdlock(3p)pthread_rwlock_timedwrlock(3p)pthread_rwlock_tryrdlock(3p)pthread_rwlock_trywrlock(3p)pthread_rwlock_unlock(3p)