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b168057a | 1 | /* Copyright (C) 2003-2015 Free Software Foundation, Inc. |
a88c9263 UD |
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 | |
59ba27a6 PE |
16 | License along with the GNU C Library; if not, see |
17 | <http://www.gnu.org/licenses/>. */ | |
a88c9263 UD |
18 | |
19 | #include <errno.h> | |
20 | #include <sysdep.h> | |
21 | #include <lowlevellock.h> | |
22 | #include <pthread.h> | |
23 | #include <pthreadP.h> | |
6af246cf | 24 | #include <sys/time.h> |
9bc6103d | 25 | #include <kernel-features.h> |
a88c9263 UD |
26 | |
27 | ||
28 | /* Try to acquire read lock for RWLOCK or return after specfied time. */ | |
29 | int | |
30 | pthread_rwlock_timedrdlock (rwlock, abstime) | |
31 | pthread_rwlock_t *rwlock; | |
32 | const struct timespec *abstime; | |
33 | { | |
34 | int result = 0; | |
35 | ||
c5be0f71 | 36 | /* Make sure we are alone. */ |
e51deae7 | 37 | lll_lock(rwlock->__data.__lock, rwlock->__data.__shared); |
a88c9263 UD |
38 | |
39 | while (1) | |
40 | { | |
7ce5c164 UD |
41 | int err; |
42 | ||
a88c9263 UD |
43 | /* Get the rwlock if there is no writer... */ |
44 | if (rwlock->__data.__writer == 0 | |
45 | /* ...and if either no writer is waiting or we prefer readers. */ | |
46 | && (!rwlock->__data.__nr_writers_queued | |
546346b6 | 47 | || PTHREAD_RWLOCK_PREFER_READER_P (rwlock))) |
a88c9263 UD |
48 | { |
49 | /* Increment the reader counter. Avoid overflow. */ | |
50 | if (++rwlock->__data.__nr_readers == 0) | |
51 | { | |
52 | /* Overflow on number of readers. */ | |
53 | --rwlock->__data.__nr_readers; | |
54 | result = EAGAIN; | |
55 | } | |
56 | ||
57 | break; | |
58 | } | |
59 | ||
60 | /* Make sure we are not holding the rwlock as a writer. This is | |
61 | a deadlock situation we recognize and report. */ | |
4ad0bbf4 UD |
62 | if (__builtin_expect (rwlock->__data.__writer |
63 | == THREAD_GETMEM (THREAD_SELF, tid), 0)) | |
a88c9263 UD |
64 | { |
65 | result = EDEADLK; | |
66 | break; | |
67 | } | |
68 | ||
69 | /* Make sure the passed in timeout value is valid. Ideally this | |
70 | test would be executed once. But since it must not be | |
71 | performed if we would not block at all simply moving the test | |
72 | to the front is no option. Replicating all the code is | |
73 | costly while this test is not. */ | |
46f4c578 | 74 | if (__builtin_expect (abstime->tv_nsec >= 1000000000 |
f3a19754 | 75 | || abstime->tv_nsec < 0, 0)) |
a88c9263 UD |
76 | { |
77 | result = EINVAL; | |
78 | break; | |
79 | } | |
80 | ||
8f861542 SP |
81 | /* Work around the fact that the kernel rejects negative timeout values |
82 | despite them being valid. */ | |
a1ffb40e | 83 | if (__glibc_unlikely (abstime->tv_sec < 0)) |
8f861542 SP |
84 | { |
85 | result = ETIMEDOUT; | |
86 | break; | |
87 | } | |
88 | ||
89 | #if (!defined __ASSUME_FUTEX_CLOCK_REALTIME \ | |
90 | || !defined lll_futex_timed_wait_bitset) | |
a88c9263 UD |
91 | /* Get the current time. So far we support only one clock. */ |
92 | struct timeval tv; | |
c5c2b7c3 | 93 | (void) __gettimeofday (&tv, NULL); |
a88c9263 UD |
94 | |
95 | /* Convert the absolute timeout value to a relative timeout. */ | |
96 | struct timespec rt; | |
97 | rt.tv_sec = abstime->tv_sec - tv.tv_sec; | |
98 | rt.tv_nsec = abstime->tv_nsec - tv.tv_usec * 1000; | |
99 | if (rt.tv_nsec < 0) | |
100 | { | |
101 | rt.tv_nsec += 1000000000; | |
102 | --rt.tv_sec; | |
103 | } | |
104 | /* Did we already time out? */ | |
105 | if (rt.tv_sec < 0) | |
106 | { | |
107 | /* Yep, return with an appropriate error. */ | |
108 | result = ETIMEDOUT; | |
109 | break; | |
110 | } | |
8f861542 | 111 | #endif |
a88c9263 UD |
112 | |
113 | /* Remember that we are a reader. */ | |
114 | if (++rwlock->__data.__nr_readers_queued == 0) | |
115 | { | |
116 | /* Overflow on number of queued readers. */ | |
117 | --rwlock->__data.__nr_readers_queued; | |
118 | result = EAGAIN; | |
119 | break; | |
120 | } | |
121 | ||
18a53579 UD |
122 | int waitval = rwlock->__data.__readers_wakeup; |
123 | ||
a88c9263 | 124 | /* Free the lock. */ |
e51deae7 | 125 | lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared); |
a88c9263 UD |
126 | |
127 | /* Wait for the writer to finish. */ | |
8f861542 SP |
128 | #if (!defined __ASSUME_FUTEX_CLOCK_REALTIME \ |
129 | || !defined lll_futex_timed_wait_bitset) | |
7ce5c164 | 130 | err = lll_futex_timed_wait (&rwlock->__data.__readers_wakeup, |
e51deae7 | 131 | waitval, &rt, rwlock->__data.__shared); |
8f861542 SP |
132 | #else |
133 | err = lll_futex_timed_wait_bitset (&rwlock->__data.__readers_wakeup, | |
134 | waitval, abstime, | |
135 | FUTEX_CLOCK_REALTIME, | |
136 | rwlock->__data.__shared); | |
137 | #endif | |
a88c9263 UD |
138 | |
139 | /* Get the lock. */ | |
e51deae7 | 140 | lll_lock (rwlock->__data.__lock, rwlock->__data.__shared); |
a88c9263 | 141 | |
644eff0c UD |
142 | --rwlock->__data.__nr_readers_queued; |
143 | ||
a88c9263 | 144 | /* Did the futex call time out? */ |
7ce5c164 | 145 | if (err == -ETIMEDOUT) |
a88c9263 UD |
146 | { |
147 | /* Yep, report it. */ | |
148 | result = ETIMEDOUT; | |
149 | break; | |
150 | } | |
151 | } | |
152 | ||
153 | /* We are done, free the lock. */ | |
e51deae7 | 154 | lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared); |
a88c9263 UD |
155 | |
156 | return result; | |
157 | } |