1 | /* Copyright (C) 2003-2016 Free Software Foundation, Inc. |
2 | This file is part of the GNU C Library. |
3 | Contributed by Martin Schwidefsky <schwidefsky@de.ibm.com>, 2003. |
4 | |
5 | The GNU C Library is free software; you can redistribute it and/or |
6 | modify it under the terms of the GNU Lesser General Public |
7 | License as published by the Free Software Foundation; either |
8 | version 2.1 of the License, or (at your option) any later version. |
9 | |
10 | The GNU C Library is distributed in the hope that it will be useful, |
11 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
13 | Lesser General Public License for more details. |
14 | |
15 | You should have received a copy of the GNU Lesser General Public |
16 | License along with the GNU C Library; if not, see |
17 | <http://www.gnu.org/licenses/>. */ |
18 | |
19 | #include <errno.h> |
20 | #include <sysdep.h> |
21 | #include <lowlevellock.h> |
22 | #include <futex-internal.h> |
23 | #include <pthread.h> |
24 | #include <pthreadP.h> |
25 | #include <sys/time.h> |
26 | #include <stdbool.h> |
27 | |
28 | |
29 | /* Try to acquire read lock for RWLOCK or return after specfied time. */ |
30 | int |
31 | pthread_rwlock_timedrdlock (pthread_rwlock_t *rwlock, |
32 | const struct timespec *abstime) |
33 | { |
34 | int result = 0; |
35 | bool wake = false; |
36 | int futex_shared = |
37 | rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED; |
38 | |
39 | /* Make sure we are alone. */ |
40 | lll_lock(rwlock->__data.__lock, rwlock->__data.__shared); |
41 | |
42 | while (1) |
43 | { |
44 | int err; |
45 | |
46 | /* Get the rwlock if there is no writer... */ |
47 | if (rwlock->__data.__writer == 0 |
48 | /* ...and if either no writer is waiting or we prefer readers. */ |
49 | && (!rwlock->__data.__nr_writers_queued |
50 | || PTHREAD_RWLOCK_PREFER_READER_P (rwlock))) |
51 | { |
52 | /* Increment the reader counter. Avoid overflow. */ |
53 | if (++rwlock->__data.__nr_readers == 0) |
54 | { |
55 | /* Overflow on number of readers. */ |
56 | --rwlock->__data.__nr_readers; |
57 | result = EAGAIN; |
58 | } |
59 | else |
60 | { |
61 | /* See pthread_rwlock_rdlock. */ |
62 | if (rwlock->__data.__nr_readers == 1 |
63 | && rwlock->__data.__nr_readers_queued > 0 |
64 | && rwlock->__data.__nr_writers_queued > 0) |
65 | { |
66 | ++rwlock->__data.__readers_wakeup; |
67 | wake = true; |
68 | } |
69 | } |
70 | |
71 | break; |
72 | } |
73 | |
74 | /* Make sure we are not holding the rwlock as a writer. This is |
75 | a deadlock situation we recognize and report. */ |
76 | if (__builtin_expect (rwlock->__data.__writer |
77 | == THREAD_GETMEM (THREAD_SELF, tid), 0)) |
78 | { |
79 | result = EDEADLK; |
80 | break; |
81 | } |
82 | |
83 | /* Make sure the passed in timeout value is valid. Ideally this |
84 | test would be executed once. But since it must not be |
85 | performed if we would not block at all simply moving the test |
86 | to the front is no option. Replicating all the code is |
87 | costly while this test is not. */ |
88 | if (__builtin_expect (abstime->tv_nsec >= 1000000000 |
89 | || abstime->tv_nsec < 0, 0)) |
90 | { |
91 | result = EINVAL; |
92 | break; |
93 | } |
94 | |
95 | /* Remember that we are a reader. */ |
96 | if (++rwlock->__data.__nr_readers_queued == 0) |
97 | { |
98 | /* Overflow on number of queued readers. */ |
99 | --rwlock->__data.__nr_readers_queued; |
100 | result = EAGAIN; |
101 | break; |
102 | } |
103 | |
104 | int waitval = rwlock->__data.__readers_wakeup; |
105 | |
106 | /* Free the lock. */ |
107 | lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared); |
108 | |
109 | /* Wait for the writer to finish. We handle ETIMEDOUT below; on other |
110 | return values, we decide how to continue based on the state of the |
111 | rwlock. */ |
112 | err = futex_abstimed_wait (&rwlock->__data.__readers_wakeup, waitval, |
113 | abstime, futex_shared); |
114 | |
115 | /* Get the lock. */ |
116 | lll_lock (rwlock->__data.__lock, rwlock->__data.__shared); |
117 | |
118 | --rwlock->__data.__nr_readers_queued; |
119 | |
120 | /* Did the futex call time out? */ |
121 | if (err == ETIMEDOUT) |
122 | { |
123 | /* Yep, report it. */ |
124 | result = ETIMEDOUT; |
125 | break; |
126 | } |
127 | } |
128 | |
129 | /* We are done, free the lock. */ |
130 | lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared); |
131 | |
132 | if (wake) |
133 | futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX, futex_shared); |
134 | |
135 | return result; |
136 | } |
137 | |