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
31 received, 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 PTHREAD_CANCEL_ASYNCHRONOUS
45 The thread can be canceled at any time. (Typically, it will be
46 canceled immediately upon receiving a cancellation request, but
47 the system doesn't guarantee this.)
48 The set-and-get operation performed by each of these functions is
50 atomic with respect to other threads in the process calling the same
51 function.
52
54 On success, these functions return 0; on error, they return a nonzero
55 error number.
56
58 The pthread_setcancelstate() can fail with the following error:
59 EINVAL Invalid value for state.
61 The pthread_setcanceltype() can fail with the following error:
63 EINVAL Invalid value for type.
65
67 POSIX.1-2001.
68
70 For details of what happens when a thread is canceled, see pthread_can‐
71 cel(3).
72 Briefly disabling cancelability is useful if a thread performs some
74 critical action that must not be interrupted by a cancellation request.
75 Beware of disabling cancelability for long periods, or around opera‐
76 tions that may block for long periods, since that will render the
77 thread unresponsive to cancellation requests.
78 Setting the cancelability type to PTHREAD_CANCEL_ASYNCHRONOUS is rarely
80 useful. Since the thread could be canceled at any time, it cannot
81 safely reserve resources (e.g., allocating memory with malloc(3)),
82 acquire mutexes, semaphores, or locks, and so on. Reserving resources
83 is unsafe because the application has no way of knowing what the state
84 of these resources is when the thread is canceled; that is, did cancel‐
85 lation occur before the resources were reserved, while they were
86 reserved, or after they were released? Furthermore, some internal data
87 structures (e.g., the linked list of free blocks managed by the mal‐
88 loc(3) family of functions) may be left in an inconsistent state if
89 cancellation occurs in the middle of the function call. Consequently,
90 clean-up handlers cease to be useful. Functions that can be safely
91 asynchronously canceled are called async-cancel-safe functions.
92 POSIX.1-2001 only requires that pthread_cancel(3), pthread_setcancel‐
93 state(), and pthread_setcanceltype() be async-cancel-safe. In general,
94 other library functions can't be safely called from an asynchronously
95 cancelable thread. One of the few circumstances in which asynchronous
96 cancelability is useful is for cancellation of a thread that is in a
97 pure compute-bound loop.
98 The Linux threading implementations permit the oldstate argument of
100 pthread_setcancelstate() to be NULL, in which case the information
101 about the previous cancelability state is not returned to the caller.
102 Many other implementations also permit a NULL oldstat argument, but
103 POSIX.1-2001 does not specify this point, so portable applications
104 should always specify a non-NULL value in oldstate. A precisely analo‐
105 gous set of statements applies for the oldtype argument of pthread_set‐
106 canceltype().
107
109 See pthread_cancel(3).
110
112 pthread_cleanup_push(3), pthread_cancel(3), pthread_testcancel(3),
113 pthreads(7)
114
116 This page is part of release 3.25 of the Linux man-pages project. A
117 description of the project, and information about reporting bugs, can
118 be found at http://www.kernel.org/doc/man-pages/.
119Linux 2008-11-24 PTHREAD_SETCANCELSTATE(3)