1pthread_setcancelstate(3) Library Functions Manual pthread_setcancelstate(3)
2
6 pthread_setcancelstate, pthread_setcanceltype - set cancelability state
7 and type
8
10 POSIX threads library (libpthread, -lpthread)
11
13 #include <pthread.h>
14 int pthread_setcancelstate(int state, int *oldstate);
16 int pthread_setcanceltype(int type, int *oldtype);
17
19 The pthread_setcancelstate() sets the cancelability state of the call‐
20 ing thread to the value given in state. The previous cancelability
21 state of the thread is returned in the buffer pointed to by oldstate.
22 The state argument must have one of the following values:
23 PTHREAD_CANCEL_ENABLE
25 The thread is cancelable. This is the default cancelability
26 state in all new threads, including the initial thread. The
27 thread's cancelability type determines when a cancelable thread
28 will respond to a cancelation request.
29 PTHREAD_CANCEL_DISABLE
31 The thread is not cancelable. If a cancelation request is re‐
32 ceived, it is blocked until cancelability is enabled.
33 The pthread_setcanceltype() sets the cancelability type of the calling
35 thread to the value given in type. The previous cancelability type of
36 the thread is returned in the buffer pointed to by oldtype. The type
37 argument must have one of the following values:
38 PTHREAD_CANCEL_DEFERRED
40 A cancelation request is deferred until the thread next calls a
41 function that is a cancelation point (see pthreads(7)). This is
42 the default cancelability type in all new threads, including the
43 initial thread.
44 Even with deferred cancelation, a cancelation point in an asyn‐
46 chronous signal handler may still be acted upon and the effect
47 is as if it was an asynchronous cancelation.
48 PTHREAD_CANCEL_ASYNCHRONOUS
50 The thread can be canceled at any time. (Typically, it will be
51 canceled immediately upon receiving a cancelation request, but
52 the system doesn't guarantee this.)
53 The set-and-get operation performed by each of these functions is
55 atomic with respect to other threads in the process calling the same
56 function.
57
59 On success, these functions return 0; on error, they return a nonzero
60 error number.
61
63 The pthread_setcancelstate() can fail with the following error:
64 EINVAL Invalid value for state.
66 The pthread_setcanceltype() can fail with the following error:
68 EINVAL Invalid value for type.
70
72 For an explanation of the terms used in this section, see at‐
73 tributes(7).
74 ┌──────────────────────────────────────┬─────────────────────┬─────────┐
76 │Interface │ Attribute │ Value │
77 ├──────────────────────────────────────┼─────────────────────┼─────────┤
78 │pthread_setcancelstate(), │ Thread safety │ MT-Safe │
79 │pthread_setcanceltype() │ │ │
80 ├──────────────────────────────────────┼─────────────────────┼─────────┤
81 │pthread_setcancelstate(), │ Async-cancel safety │ AC-Safe │
82 │pthread_setcanceltype() │ │ │
83 └──────────────────────────────────────┴─────────────────────┴─────────┘
84
86 POSIX.1-2008.
87
89 glibc 2.0 POSIX.1-2001.
90
92 For details of what happens when a thread is canceled, see pthread_can‐
93 cel(3).
94 Briefly disabling cancelability is useful if a thread performs some
96 critical action that must not be interrupted by a cancelation request.
97 Beware of disabling cancelability for long periods, or around opera‐
98 tions that may block for long periods, since that will render the
99 thread unresponsive to cancelation requests.
100 Asynchronous cancelability
102 Setting the cancelability type to PTHREAD_CANCEL_ASYNCHRONOUS is rarely
103 useful. Since the thread could be canceled at any time, it cannot
104 safely reserve resources (e.g., allocating memory with malloc(3)), ac‐
105 quire mutexes, semaphores, or locks, and so on. Reserving resources is
106 unsafe because the application has no way of knowing what the state of
107 these resources is when the thread is canceled; that is, did cancela‐
108 tion occur before the resources were reserved, while they were re‐
109 served, or after they were released? Furthermore, some internal data
110 structures (e.g., the linked list of free blocks managed by the mal‐
111 loc(3) family of functions) may be left in an inconsistent state if
112 cancelation occurs in the middle of the function call. Consequently,
113 clean-up handlers cease to be useful.
114 Functions that can be safely asynchronously canceled are called async-
116 cancel-safe functions. POSIX.1-2001 and POSIX.1-2008 require only that
117 pthread_cancel(3), pthread_setcancelstate(), and pthread_setcancel‐
118 type() be async-cancel-safe. In general, other library functions can't
119 be safely called from an asynchronously cancelable thread.
120 One of the few circumstances in which asynchronous cancelability is
122 useful is for cancelation of a thread that is in a pure compute-bound
123 loop.
124 Portability notes
126 The Linux threading implementations permit the oldstate argument of
127 pthread_setcancelstate() to be NULL, in which case the information
128 about the previous cancelability state is not returned to the caller.
129 Many other implementations also permit a NULL oldstat argument, but
130 POSIX.1 does not specify this point, so portable applications should
131 always specify a non-NULL value in oldstate. A precisely analogous set
132 of statements applies for the oldtype argument of pthread_setcancel‐
133 type().
134
136 See pthread_cancel(3).
137
139 pthread_cancel(3), pthread_cleanup_push(3), pthread_testcancel(3),
140 pthreads(7)
141Linux man-pages 6.04 2023-03-30 pthread_setcancelstate(3)