1PTHREAD_SETCANCELSTATE(3) Linux Programmer's Manual PTHREAD_SETCANCELSTATE(3)
2
6 pthread_setcancelstate, pthread_setcanceltype - set cancelability state
7 and type
8
10 #include <pthread.h>
11 int pthread_setcancelstate(int state, int *oldstate);
13 int pthread_setcanceltype(int type, int *oldtype);
14 Compile and link with -pthread.
16
18 The pthread_setcancelstate() sets the cancelability state of the call‐
19 ing thread to the value given in state. The previous cancelability
20 state of the thread is returned in the buffer pointed to by oldstate.
21 The state argument must have one of the following values:
22 PTHREAD_CANCEL_ENABLE
24 The thread is cancelable. This is the default cancelability
25 state in all new threads, including the initial thread. The
26 thread's cancelability type determines when a cancelable thread
27 will respond to a cancellation request.
28 PTHREAD_CANCEL_DISABLE
30 The thread is not cancelable. If a cancellation request is re‐
31 ceived, it is blocked until cancelability is enabled.
32 The pthread_setcanceltype() sets the cancelability type of the calling
34 thread to the value given in type. The previous cancelability type of
35 the thread is returned in the buffer pointed to by oldtype. The type
36 argument must have one of the following values:
37 PTHREAD_CANCEL_DEFERRED
39 A cancellation request is deferred until the thread next calls a
40 function that is a cancellation point (see pthreads(7)). This
41 is the default cancelability type in all new threads, including
42 the initial thread.
43 Even with deferred cancellation, a cancellation point in an
45 asynchronous signal handler may still be acted upon and the ef‐
46 fect is as if it was an asynchronous cancellation.
47 PTHREAD_CANCEL_ASYNCHRONOUS
49 The thread can be canceled at any time. (Typically, it will be
50 canceled immediately upon receiving a cancellation request, but
51 the system doesn't guarantee this.)
52 The set-and-get operation performed by each of these functions is
54 atomic with respect to other threads in the process calling the same
55 function.
56
58 On success, these functions return 0; on error, they return a nonzero
59 error number.
60
62 The pthread_setcancelstate() can fail with the following error:
63 EINVAL Invalid value for state.
65 The pthread_setcanceltype() can fail with the following error:
67 EINVAL Invalid value for type.
69
71 For an explanation of the terms used in this section, see at‐
72 tributes(7).
73 ┌──────────────────────────┬─────────────────────┬─────────┐
75 │Interface │ Attribute │ Value │
76 ├──────────────────────────┼─────────────────────┼─────────┤
77 │pthread_setcancelstate(), │ Thread safety │ MT-Safe │
78 │pthread_setcanceltype() │ │ │
79 ├──────────────────────────┼─────────────────────┼─────────┤
80 │pthread_setcancelstate(), │ Async-cancel-safety │ AC-Safe │
81 │pthread_setcanceltype() │ │ │
82 └──────────────────────────┴─────────────────────┴─────────┘
84 POSIX.1-2001, POSIX.1-2008.
85
87 For details of what happens when a thread is canceled, see pthread_can‐
88 cel(3).
89 Briefly disabling cancelability is useful if a thread performs some
91 critical action that must not be interrupted by a cancellation request.
92 Beware of disabling cancelability for long periods, or around opera‐
93 tions that may block for long periods, since that will render the
94 thread unresponsive to cancellation requests.
95 Asynchronous cancelability
97 Setting the cancelability type to PTHREAD_CANCEL_ASYNCHRONOUS is rarely
98 useful. Since the thread could be canceled at any time, it cannot
99 safely reserve resources (e.g., allocating memory with malloc(3)), ac‐
100 quire mutexes, semaphores, or locks, and so on. Reserving resources is
101 unsafe because the application has no way of knowing what the state of
102 these resources is when the thread is canceled; that is, did cancella‐
103 tion occur before the resources were reserved, while they were re‐
104 served, or after they were released? Furthermore, some internal data
105 structures (e.g., the linked list of free blocks managed by the mal‐
106 loc(3) family of functions) may be left in an inconsistent state if
107 cancellation occurs in the middle of the function call. Consequently,
108 clean-up handlers cease to be useful.
109 Functions that can be safely asynchronously canceled are called async-
111 cancel-safe functions. POSIX.1-2001 and POSIX.1-2008 require only that
112 pthread_cancel(3), pthread_setcancelstate(), and pthread_setcancel‐
113 type() be async-cancel-safe. In general, other library functions can't
114 be safely called from an asynchronously cancelable thread.
115 One of the few circumstances in which asynchronous cancelability is
117 useful is for cancellation of a thread that is in a pure compute-bound
118 loop.
119 Portability notes
121 The Linux threading implementations permit the oldstate argument of
122 pthread_setcancelstate() to be NULL, in which case the information
123 about the previous cancelability state is not returned to the caller.
124 Many other implementations also permit a NULL oldstat argument, but
125 POSIX.1 does not specify this point, so portable applications should
126 always specify a non-NULL value in oldstate. A precisely analogous set
127 of statements applies for the oldtype argument of pthread_setcancel‐
128 type().
129
131 See pthread_cancel(3).
132
134 pthread_cancel(3), pthread_cleanup_push(3), pthread_testcancel(3),
135 pthreads(7)
136
138 This page is part of release 5.10 of the Linux man-pages project. A
139 description of the project, information about reporting bugs, and the
140 latest version of this page, can be found at
141 https://www.kernel.org/doc/man-pages/.
142Linux 2020-06-09 PTHREAD_SETCANCELSTATE(3)