1PTHREAD_MUTEXATTR_SETROBUST(L3i)nux Programmer's ManPuTaHlREAD_MUTEXATTR_SETROBUST(3)
2
6 pthread_mutexattr_getrobust, pthread_mutexattr_setrobust - get and set
7 the robustness attribute of a mutex attributes object
8
10 #include <pthread.h>
11 int pthread_mutexattr_getrobust(const pthread_mutexattr_t *attr,
13 int *robustness);
14 int pthread_mutexattr_setrobust(pthread_mutexattr_t *attr,
15 int robustness);
16 Compile and link with -pthread.
18 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
20 pthread_mutexattr_getrobust(), pthread_mutexattr_setrobust():
22 _POSIX_C_SOURCE >= 200809L
23
25 The pthread_mutexattr_getrobust() function places the value of the ro‐
26 bustness attribute of the mutex attributes object referred to by attr
27 in *robustness. The pthread_mutexattr_setrobust() function sets the
28 value of the robustness attribute of the mutex attributes object re‐
29 ferred to by attr to the value specified in *robustness.
30 The robustness attribute specifies the behavior of the mutex when the
32 owning thread dies without unlocking the mutex. The following values
33 are valid for robustness:
34 PTHREAD_MUTEX_STALLED
36 This is the default value for a mutex attributes object. If a
37 mutex is initialized with the PTHREAD_MUTEX_STALLED attribute
38 and its owner dies without unlocking it, the mutex remains
39 locked afterwards and any future attempts to call pthread_mu‐
40 tex_lock(3) on the mutex will block indefinitely.
41 PTHREAD_MUTEX_ROBUST
43 If a mutex is initialized with the PTHREAD_MUTEX_ROBUST attri‐
44 bute and its owner dies without unlocking it, any future at‐
45 tempts to call pthread_mutex_lock(3) on this mutex will succeed
46 and return EOWNERDEAD to indicate that the original owner no
47 longer exists and the mutex is in an inconsistent state. Usu‐
48 ally after EOWNERDEAD is returned, the next owner should call
49 pthread_mutex_consistent(3) on the acquired mutex to make it
50 consistent again before using it any further.
51 If the next owner unlocks the mutex using pthread_mutex_un‐
53 lock(3) before making it consistent, the mutex will be perma‐
54 nently unusable and any subsequent attempts to lock it using
55 pthread_mutex_lock(3) will fail with the error ENOTRECOVERABLE.
56 The only permitted operation on such a mutex is pthread_mu‐
57 tex_destroy(3).
58 If the next owner terminates before calling pthread_mutex_con‐
60 sistent(3), further pthread_mutex_lock(3) operations on this mu‐
61 tex will still return EOWNERDEAD.
62 Note that the attr argument of pthread_mutexattr_getrobust() and
64 pthread_mutexattr_setrobust() should refer to a mutex attributes object
65 that was initialized by pthread_mutexattr_init(3), otherwise the behav‐
66 ior is undefined.
67
69 On success, these functions return 0. On error, they return a positive
70 error number.
71 In the glibc implementation, pthread_mutexattr_getrobust() always re‐
73 turn zero.
74
76 EINVAL A value other than PTHREAD_MUTEX_STALLED or PTHREAD_MUTEX_ROBUST
77 was passed to pthread_mutexattr_setrobust().
78
80 pthread_mutexattr_getrobust() and pthread_mutexattr_setrobust() were
81 added to glibc in version 2.12.
82
84 POSIX.1-2008.
85
87 In the Linux implementation, when using process-shared robust mutexes,
88 a waiting thread also receives the EOWNERDEAD notification if the owner
89 of a robust mutex performs an execve(2) without first unlocking the mu‐
90 tex. POSIX.1 does not specify this detail, but the same behavior also
91 occurs in at least some other implementations.
92 Before the addition of pthread_mutexattr_getrobust() and pthread_mutex‐
94 attr_setrobust() to POSIX, glibc defined the following equivalent non‐
95 standard functions if _GNU_SOURCE was defined:
96 int pthread_mutexattr_getrobust_np(const pthread_mutexattr_t *attr,
98 int *robustness);
99 int pthread_mutexattr_setrobust_np(const pthread_mutexattr_t *attr,
100 int robustness);
101 Correspondingly, the constants PTHREAD_MUTEX_STALLED_NP and PTHREAD_MU‐
103 TEX_ROBUST_NP were also defined.
104 These GNU-specific APIs, which first appeared in glibc 2.4, are nowa‐
106 days obsolete and should not be used in new programs; since glibc 2.34
107 these APIs are marked as deprecated.
108
110 The program below demonstrates the use of the robustness attribute of a
111 mutex attributes object. In this program, a thread holding the mutex
112 dies prematurely without unlocking the mutex. The main thread subse‐
113 quently acquires the mutex successfully and gets the error EOWNERDEAD,
114 after which it makes the mutex consistent.
115 The following shell session shows what we see when running this pro‐
117 gram:
118 $ ./a.out
120 [original owner] Setting lock...
121 [original owner] Locked. Now exiting without unlocking.
122 [main] Attempting to lock the robust mutex.
123 [main] pthread_mutex_lock() returned EOWNERDEAD
124 [main] Now make the mutex consistent
125 [main] Mutex is now consistent; unlocking
126 Program source
128 #include <stdlib.h>
129 #include <stdio.h>
130 #include <unistd.h>
131 #include <pthread.h>
132 #include <errno.h>
133 #define handle_error_en(en, msg) \
135 do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)
136 static pthread_mutex_t mtx;
138 static void *
140 original_owner_thread(void *ptr)
141 {
142 printf("[original owner] Setting lock...\n");
143 pthread_mutex_lock(&mtx);
144 printf("[original owner] Locked. Now exiting without unlocking.\n");
145 pthread_exit(NULL);
146 }
147 int
149 main(int argc, char *argv[])
150 {
151 pthread_t thr;
152 pthread_mutexattr_t attr;
153 int s;
154 pthread_mutexattr_init(&attr);
156 pthread_mutexattr_setrobust(&attr, PTHREAD_MUTEX_ROBUST);
158 pthread_mutex_init(&mtx, &attr);
160 pthread_create(&thr, NULL, original_owner_thread, NULL);
162 sleep(2);
164 /* "original_owner_thread" should have exited by now. */
166 printf("[main] Attempting to lock the robust mutex.\n");
168 s = pthread_mutex_lock(&mtx);
169 if (s == EOWNERDEAD) {
170 printf("[main] pthread_mutex_lock() returned EOWNERDEAD\n");
171 printf("[main] Now make the mutex consistent\n");
172 s = pthread_mutex_consistent(&mtx);
173 if (s != 0)
174 handle_error_en(s, "pthread_mutex_consistent");
175 printf("[main] Mutex is now consistent; unlocking\n");
176 s = pthread_mutex_unlock(&mtx);
177 if (s != 0)
178 handle_error_en(s, "pthread_mutex_unlock");
179 exit(EXIT_SUCCESS);
181 } else if (s == 0) {
182 printf("[main] pthread_mutex_lock() unexpectedly succeeded\n");
183 exit(EXIT_FAILURE);
184 } else {
185 printf("[main] pthread_mutex_lock() unexpectedly failed\n");
186 handle_error_en(s, "pthread_mutex_lock");
187 }
188 }
189
191 get_robust_list(2), set_robust_list(2), pthread_mutex_consistent(3),
192 pthread_mutex_init(3), pthread_mutex_lock(3), pthreads(7)
193
195 This page is part of release 5.13 of the Linux man-pages project. A
196 description of the project, information about reporting bugs, and the
197 latest version of this page, can be found at
198 https://www.kernel.org/doc/man-pages/.
199Linux 2021-03-22 PTHREAD_MUTEXATTR_SETROBUST(3)