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 write lock for RWLOCK or return after specfied time. */ |
30 | int |
31 | pthread_rwlock_timedwrlock (pthread_rwlock_t *rwlock, |
32 | const struct timespec *abstime) |
33 | { |
34 | int result = 0; |
35 | bool wake_readers = 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 and no reader. */ |
47 | if (rwlock->__data.__writer == 0 && rwlock->__data.__nr_readers == 0) |
48 | { |
49 | /* Mark self as writer. */ |
50 | rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid); |
51 | break; |
52 | } |
53 | |
54 | /* Make sure we are not holding the rwlock as a writer. This is |
55 | a deadlock situation we recognize and report. */ |
56 | if (__builtin_expect (rwlock->__data.__writer |
57 | == THREAD_GETMEM (THREAD_SELF, tid), 0)) |
58 | { |
59 | result = EDEADLK; |
60 | break; |
61 | } |
62 | |
63 | /* Make sure the passed in timeout value is valid. Ideally this |
64 | test would be executed once. But since it must not be |
65 | performed if we would not block at all simply moving the test |
66 | to the front is no option. Replicating all the code is |
67 | costly while this test is not. */ |
68 | if (__builtin_expect (abstime->tv_nsec >= 1000000000 |
69 | || abstime->tv_nsec < 0, 0)) |
70 | { |
71 | result = EINVAL; |
72 | break; |
73 | } |
74 | |
75 | /* Remember that we are a writer. */ |
76 | if (++rwlock->__data.__nr_writers_queued == 0) |
77 | { |
78 | /* Overflow on number of queued writers. */ |
79 | --rwlock->__data.__nr_writers_queued; |
80 | result = EAGAIN; |
81 | break; |
82 | } |
83 | |
84 | int waitval = rwlock->__data.__writer_wakeup; |
85 | |
86 | /* Free the lock. */ |
87 | lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared); |
88 | |
89 | /* Wait for the writer or reader(s) to finish. We handle ETIMEDOUT |
90 | below; on other return values, we decide how to continue based on |
91 | the state of the rwlock. */ |
92 | err = futex_abstimed_wait (&rwlock->__data.__writer_wakeup, waitval, |
93 | abstime, futex_shared); |
94 | |
95 | /* Get the lock. */ |
96 | lll_lock (rwlock->__data.__lock, rwlock->__data.__shared); |
97 | |
98 | /* To start over again, remove the thread from the writer list. */ |
99 | --rwlock->__data.__nr_writers_queued; |
100 | |
101 | /* Did the futex call time out? */ |
102 | if (err == ETIMEDOUT) |
103 | { |
104 | result = ETIMEDOUT; |
105 | /* If we prefer writers, it can have happened that readers blocked |
106 | for us to acquire the lock first. If we have timed out, we need |
107 | to wake such readers if there are any, and if there is no writer |
108 | currently (otherwise, the writer will take care of wake-up). |
109 | Likewise, even if we prefer readers, we can be responsible for |
110 | wake-up (see pthread_rwlock_unlock) if no reader or writer has |
111 | acquired the lock. We have timed out and thus not consumed a |
112 | futex wake-up; therefore, if there is no other blocked writer |
113 | that would consume the wake-up and thus take over responsibility, |
114 | we need to wake blocked readers. */ |
115 | if ((!PTHREAD_RWLOCK_PREFER_READER_P (rwlock) |
116 | || ((rwlock->__data.__nr_readers == 0) |
117 | && (rwlock->__data.__nr_writers_queued == 0))) |
118 | && (rwlock->__data.__nr_readers_queued > 0) |
119 | && (rwlock->__data.__writer == 0)) |
120 | { |
121 | ++rwlock->__data.__readers_wakeup; |
122 | wake_readers = true; |
123 | } |
124 | break; |
125 | } |
126 | } |
127 | |
128 | /* We are done, free the lock. */ |
129 | lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared); |
130 | |
131 | /* Might be required after timeouts. */ |
132 | if (wake_readers) |
133 | futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX, futex_shared); |
134 | |
135 | return result; |
136 | } |
137 | |