1 | /* Copyright (C) 2015-2022 Free Software Foundation, Inc. |
2 | This file is part of the GNU C Library. |
3 | |
4 | The GNU C Library is free software; you can redistribute it and/or |
5 | modify it under the terms of the GNU Lesser General Public |
6 | License as published by the Free Software Foundation; either |
7 | version 2.1 of the License, or (at your option) any later version. |
8 | |
9 | The GNU C Library is distributed in the hope that it will be useful, |
10 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
11 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
12 | Lesser General Public License for more details. |
13 | |
14 | You should have received a copy of the GNU Lesser General Public |
15 | License along with the GNU C Library; if not, see |
16 | <https://www.gnu.org/licenses/>. */ |
17 | |
18 | /* This tests that a writer that is preferred -- but times out due to a |
19 | reader being present -- does not miss to wake other readers blocked on the |
20 | writer's pending lock acquisition. */ |
21 | |
22 | #include <errno.h> |
23 | #include <pthread.h> |
24 | #include <stdio.h> |
25 | #include <stdlib.h> |
26 | #include <time.h> |
27 | |
28 | /* The bug existed in the code that strictly prefers writers over readers. */ |
29 | static pthread_rwlock_t r = PTHREAD_RWLOCK_WRITER_NONRECURSIVE_INITIALIZER_NP; |
30 | |
31 | static void * |
32 | writer (void *arg) |
33 | { |
34 | struct timespec ts; |
35 | if (clock_gettime (CLOCK_REALTIME, tp: &ts) != 0) |
36 | { |
37 | puts (s: "clock_gettime failed" ); |
38 | exit (EXIT_FAILURE); |
39 | } |
40 | ts.tv_sec += 1; |
41 | int e = pthread_rwlock_timedwrlock (rwlock: &r, abstime: &ts); |
42 | if (e != ETIMEDOUT) |
43 | { |
44 | puts (s: "timedwrlock did not time out" ); |
45 | exit (EXIT_FAILURE); |
46 | } |
47 | return NULL; |
48 | } |
49 | |
50 | static void * |
51 | reader (void *arg) |
52 | { |
53 | /* This isn't a reliable way to get the interleaving we need (because a |
54 | failed trylock doesn't synchronize with the writer, and because we could |
55 | try to lock after the writer has already timed out). However, both will |
56 | just lead to false positives. */ |
57 | int e; |
58 | while ((e = pthread_rwlock_tryrdlock (rwlock: &r)) != EBUSY) |
59 | { |
60 | if (e != 0) |
61 | exit (EXIT_FAILURE); |
62 | pthread_rwlock_unlock (rwlock: &r); |
63 | } |
64 | e = pthread_rwlock_rdlock (rwlock: &r); |
65 | if (e != 0) |
66 | { |
67 | puts (s: "reader rdlock failed" ); |
68 | exit (EXIT_FAILURE); |
69 | } |
70 | pthread_rwlock_unlock (rwlock: &r); |
71 | return NULL; |
72 | } |
73 | |
74 | |
75 | static int |
76 | do_test (void) |
77 | { |
78 | /* Grab a rdlock, then create a writer and a reader, and wait until they |
79 | finished. */ |
80 | |
81 | if (pthread_rwlock_rdlock (rwlock: &r) != 0) |
82 | { |
83 | puts (s: "initial rdlock failed" ); |
84 | return 1; |
85 | } |
86 | |
87 | pthread_t thw; |
88 | if (pthread_create (newthread: &thw, NULL, start_routine: writer, NULL) != 0) |
89 | { |
90 | puts (s: "create failed" ); |
91 | return 1; |
92 | } |
93 | pthread_t thr; |
94 | if (pthread_create (newthread: &thr, NULL, start_routine: reader, NULL) != 0) |
95 | { |
96 | puts (s: "create failed" ); |
97 | return 1; |
98 | } |
99 | |
100 | if (pthread_join (th: thw, NULL) != 0) |
101 | { |
102 | puts (s: "writer join failed" ); |
103 | return 1; |
104 | } |
105 | if (pthread_join (th: thr, NULL) != 0) |
106 | { |
107 | puts (s: "reader join failed" ); |
108 | return 1; |
109 | } |
110 | |
111 | return 0; |
112 | } |
113 | |
114 | |
115 | #define TEST_FUNCTION do_test () |
116 | #include "../test-skeleton.c" |
117 | |