Manual Pages for UNIX Operating System command usage for man pthread_rwlock_rdlock

Standard C Library Functions            pthread_rwlock_rdlock(3C)



NAME
     pthread_rwlock_rdlock, pthread_rwlock_tryrdlock  -  lock  or
     attempt to lock read-write lock object for reading

SYNOPSIS
     cc -mt [ flag... ] file... -lpthread [ library... ]
     #include 

     int pthread_rwlock_rdlock(pthread_rwlock_t *rwlock);


     int pthread_rwlock_tryrdlock(pthread_rwlock_t *rwlock);


DESCRIPTION
     The pthread_rwlock_rdlock() function applies 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.


     The calling thread does 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  acquires
     the  lock.  If  the  read  lock is not acquired, the calling
     thread blocks until it can acquire the lock.


     A thread can hold multiple concurrent read locks  on  rwlock
     (that  is,  successfully  call  the  pthread_rwlock_rdlock()
     function n times). If so, the thread must  perform  matching
     unlocks  (that is, it must call the  pthread_rwlock_unlock()
     function n times).


     The maximum number of concurrent read locks  that  a  thread
     can hold on one read-write lock is currently set at 100,000,
     though this number could change in a future  release.  There
     is  no imposed limit on the number of different threads that
     can apply a read lock to one read-write lock.


     The pthread_rwlock_tryrdlock() function applies a read  lock
     like  the  pthread_rwlock_rdlock() function, with the excep-
     tion   that   the   function   fails   if   the   equivalent
     pthread_rwlock_rdlock()  call would have blocked the calling
     thread.  In  no  case  will  the  pthread_rwlock_tryrdlock()
     function  ever  bloc.  It always either acquires the lock or
     fails and returns immediately.






SunOS 5.11          Last change: 23 Mar 2005                    1






Standard C Library Functions            pthread_rwlock_rdlock(3C)



     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 read-
     ing as if it was not interrupted.

RETURN VALUES
     If successful, the pthread_rwlock_rdlock() function  returns
     0.  Otherwise,  an  error number is returned to indicate the
     error.


     The pthread_rwlock_tryrdlock() function  returns  0  if  the
     lock for reading on the read-write lock object referenced by
     rwlock is acquired.  Otherwise an error number  is  returned
     to indicate the error.

ERRORS
     The pthread_rwlock_rdlock()  and  pthread_rwlock_tryrdlock()
     functions will fail if:

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



     The pthread_rwlock_rdlock() function will fail if:

     EDEADLK    The current thread already  owns  the  read-write
                lock for writing.



     The pthread_rwlock_tryrdlock() function will fail if:

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


ATTRIBUTES
     See  attributes(5) for descriptions of the following  attri-
     butes:








SunOS 5.11          Last change: 23 Mar 2005                    2






Standard C Library Functions            pthread_rwlock_rdlock(3C)



     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    |_____________________________|_____________________________|
    | Interface Stability         | Committed                   |
    |_____________________________|_____________________________|
    | MT-Level                    | MT-Safe                     |
    |_____________________________|_____________________________|
    | Standard                    | See standards(5).           |
    |_____________________________|_____________________________|


SEE ALSO
     pthread_rwlock_init(3C),          pthread_rwlock_wrlock(3C),
     pthread_rwlockattr_init(3C),      pthread_rwlock_unlock(3C),
     attributes(5), standards(5)








































SunOS 5.11          Last change: 23 Mar 2005                    3