1pthread_rwlock_rdlock(3C)Standard C Library Functionspthread_rwlock_rdlock(3C)
2
6 pthread_rwlock_rdlock, pthread_rwlock_tryrdlock - lock or attempt to
7 lock read-write lock object for reading
8
10 cc -mt [ flag... ] file... -lpthread [ library... ]
11 #include <pthread.h>
12 int pthread_rwlock_rdlock(pthread_rwlock_t *rwlock);
14 int pthread_rwlock_tryrdlock(pthread_rwlock_t *rwlock);
17
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.
24 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.
30 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).
36 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.
43 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.
51 Results are undefined if any of these functions are called with an
54 uninitialized read-write lock.
55 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.
60
62 If successful, the pthread_rwlock_rdlock() function returns 0. Other‐
63 wise, an error number is returned to indicate the error.
64 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.
69
71 The pthread_rwlock_rdlock() and pthread_rwlock_tryrdlock() functions
72 will fail if:
73 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.
77 The pthread_rwlock_rdlock() function will fail if:
81 EDEADLK The current thread already owns the read-write lock for
83 writing.
84 The pthread_rwlock_tryrdlock() function will fail if:
88 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.
92
95 See attributes(5) for descriptions of the following attributes:
96 ┌─────────────────────────────┬─────────────────────────────┐
101 │ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
102 ├─────────────────────────────┼─────────────────────────────┤
103 │Interface Stability │Standard │
104 ├─────────────────────────────┼─────────────────────────────┤
105 │MT-Level │MT-Safe │
106 └─────────────────────────────┴─────────────────────────────┘
107
109 pthread_rwlock_init(3C), pthread_rwlock_wrlock(3C), pthread_rwlock‐
110 attr_init(3C), pthread_rwlock_unlock(3C), attributes(5), standards(5)
111SunOS 5.11 23 Mar 2005 pthread_rwlock_rdlock(3C)