1pthread_rwlock_rdlock(3C)Standard C Library Functionspthread_rwlock_rdlock(3C)
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NAME

6       pthread_rwlock_rdlock,  pthread_rwlock_tryrdlock  -  lock or attempt to
7       lock read-write lock object for reading
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SYNOPSIS

10       cc -mt [ flag... ] file... -lpthread [ library... ]
11       #include <pthread.h>
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13       int pthread_rwlock_rdlock(pthread_rwlock_t *rwlock);
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16       int pthread_rwlock_tryrdlock(pthread_rwlock_t *rwlock);
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DESCRIPTION

20       The pthread_rwlock_rdlock() function applies a read lock to  the  read-
21       write  lock referenced by rwlock.  The calling thread acquires the read
22       lock if a writer does not hold  the  lock  and  there  are  no  writers
23       blocked on the lock.
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26       The calling thread does not acquire the lock if a writer holds the lock
27       or if writers of higher or equal priority are blocked on the lock; oth‐
28       erwise,  the  calling thread acquires the lock. If the read lock is not
29       acquired, the calling thread blocks until it can acquire the lock.
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32       A thread can hold multiple concurrent read locks on  rwlock  (that  is,
33       successfully call the pthread_rwlock_rdlock() function n times). If so,
34       the thread must perform matching unlocks (that is,  it  must  call  the
35       pthread_rwlock_unlock() function n times).
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38       The  maximum  number of concurrent read locks that a thread can hold on
39       one read-write lock is currently set at  100,000,  though  this  number
40       could change in a future release. There is no imposed limit on the num‐
41       ber of different threads that can apply a read lock to  one  read-write
42       lock.
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45       The  pthread_rwlock_tryrdlock()  function  applies a read lock like the
46       pthread_rwlock_rdlock() function, with the exception that the  function
47       fails if the equivalent pthread_rwlock_rdlock() call would have blocked
48       the calling thread.  In no  case  will  the  pthread_rwlock_tryrdlock()
49       function  ever  bloc.  It  always either acquires the lock or fails and
50       returns immediately.
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53       Results are undefined if any of these  functions  are  called  with  an
54       uninitialized read-write lock.
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57       If  a signal is delivered to a thread waiting for a read-write lock for
58       reading, upon return from the signal handler the thread resumes waiting
59       for the read-write lock for reading as if it was not interrupted.
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RETURN VALUES

62       If  successful,  the pthread_rwlock_rdlock() function returns 0. Other‐
63       wise, an error number is returned to indicate the error.
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66       The pthread_rwlock_tryrdlock() function returns 0 if the lock for read‐
67       ing  on  the  read-write  lock object referenced by rwlock is acquired.
68       Otherwise an error number  is returned to indicate the error.
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ERRORS

71       The pthread_rwlock_rdlock()  and  pthread_rwlock_tryrdlock()  functions
72       will fail if:
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74       EAGAIN    The  read lock could not be acquired because the maximum num‐
75                 ber of read locks by the current thread for rwlock  has  been
76                 exceeded.
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80       The pthread_rwlock_rdlock() function will fail if:
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82       EDEADLK    The  current  thread  already  owns  the read-write lock for
83                  writing.
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87       The pthread_rwlock_tryrdlock() function will fail if:
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89       EBUSY    The read-write lock could not be acquired for reading  because
90                a  writer holds the lock or a writer with the appropriate pri‐
91                ority was blocked on it.
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ATTRIBUTES

95       See  attributes(5) for descriptions of the following attributes:
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100       ┌─────────────────────────────┬─────────────────────────────┐
101       │      ATTRIBUTE TYPE         │      ATTRIBUTE VALUE        │
102       ├─────────────────────────────┼─────────────────────────────┤
103       │Interface Stability          │Standard                     │
104       ├─────────────────────────────┼─────────────────────────────┤
105       │MT-Level                     │MT-Safe                      │
106       └─────────────────────────────┴─────────────────────────────┘
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SEE ALSO

109       pthread_rwlock_init(3C),   pthread_rwlock_wrlock(3C),   pthread_rwlock‐
110       attr_init(3C), pthread_rwlock_unlock(3C), attributes(5), standards(5)
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114SunOS 5.11                        23 Mar 2005        pthread_rwlock_rdlock(3C)