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 └──────────────────────────────────────┴─────────────────────┴─────────┘
83
85 POSIX.1-2001, POSIX.1-2008.
86
88 For details of what happens when a thread is canceled, see pthread_can‐
89 cel(3).
90 Briefly disabling cancelability is useful if a thread performs some
92 critical action that must not be interrupted by a cancellation request.
93 Beware of disabling cancelability for long periods, or around opera‐
94 tions that may block for long periods, since that will render the
95 thread unresponsive to cancellation requests.
96 Asynchronous cancelability
98 Setting the cancelability type to PTHREAD_CANCEL_ASYNCHRONOUS is rarely
99 useful. Since the thread could be canceled at any time, it cannot
100 safely reserve resources (e.g., allocating memory with malloc(3)), ac‐
101 quire mutexes, semaphores, or locks, and so on. Reserving resources is
102 unsafe because the application has no way of knowing what the state of
103 these resources is when the thread is canceled; that is, did cancella‐
104 tion occur before the resources were reserved, while they were re‐
105 served, or after they were released? Furthermore, some internal data
106 structures (e.g., the linked list of free blocks managed by the mal‐
107 loc(3) family of functions) may be left in an inconsistent state if
108 cancellation occurs in the middle of the function call. Consequently,
109 clean-up handlers cease to be useful.
110 Functions that can be safely asynchronously canceled are called async-
112 cancel-safe functions. POSIX.1-2001 and POSIX.1-2008 require only that
113 pthread_cancel(3), pthread_setcancelstate(), and pthread_setcancel‐
114 type() be async-cancel-safe. In general, other library functions can't
115 be safely called from an asynchronously cancelable thread.
116 One of the few circumstances in which asynchronous cancelability is
118 useful is for cancellation of a thread that is in a pure compute-bound
119 loop.
120 Portability notes
122 The Linux threading implementations permit the oldstate argument of
123 pthread_setcancelstate() to be NULL, in which case the information
124 about the previous cancelability state is not returned to the caller.
125 Many other implementations also permit a NULL oldstat argument, but
126 POSIX.1 does not specify this point, so portable applications should
127 always specify a non-NULL value in oldstate. A precisely analogous set
128 of statements applies for the oldtype argument of pthread_setcancel‐
129 type().
130
132 See pthread_cancel(3).
133
135 pthread_cancel(3), pthread_cleanup_push(3), pthread_testcancel(3),
136 pthreads(7)
137
139 This page is part of release 5.12 of the Linux man-pages project. A
140 description of the project, information about reporting bugs, and the
141 latest version of this page, can be found at
142 https://www.kernel.org/doc/man-pages/.
143Linux 2021-03-22 PTHREAD_SETCANCELSTATE(3)