1PTHREAD_SETCANCELSTATE(3P) POSIX Programmer's ManualPTHREAD_SETCANCELSTATE(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 pthread_setcancelstate, pthread_setcanceltype, pthread_testcancel — set
13 cancelability state
14
16 #include <pthread.h>
17 int pthread_setcancelstate(int state, int *oldstate);
19 int pthread_setcanceltype(int type, int *oldtype);
20 void pthread_testcancel(void);
21
23 The pthread_setcancelstate() function shall atomically both set the
24 calling thread's cancelability state to the indicated state and return
25 the previous cancelability state at the location referenced by old‐
26 state. Legal values for state are PTHREAD_CANCEL_ENABLE and
27 PTHREAD_CANCEL_DISABLE.
28 The pthread_setcanceltype() function shall atomically both set the
30 calling thread's cancelability type to the indicated type and return
31 the previous cancelability type at the location referenced by oldtype.
32 Legal values for type are PTHREAD_CANCEL_DEFERRED and PTHREAD_CAN‐
33 CEL_ASYNCHRONOUS.
34 The cancelability state and type of any newly created threads, includ‐
36 ing the thread in which main() was first invoked, shall be PTHREAD_CAN‐
37 CEL_ENABLE and PTHREAD_CANCEL_DEFERRED respectively.
38 The pthread_testcancel() function shall create a cancellation point in
40 the calling thread. The pthread_testcancel() function shall have no
41 effect if cancelability is disabled.
42
44 If successful, the pthread_setcancelstate() and pthread_setcanceltype()
45 functions shall return zero; otherwise, an error number shall be
46 returned to indicate the error.
47
49 The pthread_setcancelstate() function may fail if:
50 EINVAL The specified state is not PTHREAD_CANCEL_ENABLE or PTHREAD_CAN‐
52 CEL_DISABLE.
53 The pthread_setcanceltype() function may fail if:
55 EINVAL The specified type is not PTHREAD_CANCEL_DEFERRED or
57 PTHREAD_CANCEL_ASYNCHRONOUS.
58 These functions shall not return an error code of [EINTR].
60 The following sections are informative.
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64 None.
65
67 In order to write a signal handler for an asynchronous signal which can
68 run safely in a cancellable thread, pthread_setcancelstate() must be
69 used to disable cancellation for the duration of any calls that the
70 signal handler makes which are cancellation points. However, the stan‐
71 dard does not permit strictly conforming applications to call
72 pthread_setcancelstate() from a signal handler since it is not cur‐
73 rently required to be async-signal-safe. On implementations where
74 pthread_setcancelstate() is not async-signal-safe, alternatives are to
75 ensure either that the corresponding signals are blocked during execu‐
76 tion of functions that are not async-cancel-safe or that cancellation
77 is disabled during times when those signals could be delivered. Imple‐
78 mentations are strongly encouraged to make pthread_setcancelstate()
79 async-signal-safe.
80
82 The pthread_setcancelstate() and pthread_setcanceltype() functions con‐
83 trol the points at which a thread may be asynchronously canceled. For
84 cancellation control to be usable in modular fashion, some rules need
85 to be followed.
86 An object can be considered to be a generalization of a procedure. It
88 is a set of procedures and global variables written as a unit and
89 called by clients not known by the object. Objects may depend on other
90 objects.
91 First, cancelability should only be disabled on entry to an object,
93 never explicitly enabled. On exit from an object, the cancelability
94 state should always be restored to its value on entry to the object.
95 This follows from a modularity argument: if the client of an object (or
97 the client of an object that uses that object) has disabled cancelabil‐
98 ity, it is because the client does not want to be concerned about
99 cleaning up if the thread is canceled while executing some sequence of
100 actions. If an object is called in such a state and it enables cancela‐
101 bility and a cancellation request is pending for that thread, then the
102 thread is canceled, contrary to the wish of the client that disabled.
103 Second, the cancelability type may be explicitly set to either deferred
105 or asynchronous upon entry to an object. But as with the cancelability
106 state, on exit from an object the cancelability type should always be
107 restored to its value on entry to the object.
108 Finally, only functions that are cancel-safe may be called from a
110 thread that is asynchronously cancelable.
111
113 The pthread_setcancelstate() function may be added to the table of
114 async-signal-safe functions in Section 2.4.3, Signal Actions.
115
117 pthread_cancel()
118 The Base Definitions volume of POSIX.1‐2017, <pthread.h>
120
122 Portions of this text are reprinted and reproduced in electronic form
123 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
124 table Operating System Interface (POSIX), The Open Group Base Specifi‐
125 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
126 Electrical and Electronics Engineers, Inc and The Open Group. In the
127 event of any discrepancy between this version and the original IEEE and
128 The Open Group Standard, the original IEEE and The Open Group Standard
129 is the referee document. The original Standard can be obtained online
130 at http://www.opengroup.org/unix/online.html .
131 Any typographical or formatting errors that appear in this page are
133 most likely to have been introduced during the conversion of the source
134 files to man page format. To report such errors, see https://www.ker‐
135 nel.org/doc/man-pages/reporting_bugs.html .
136IEEE/The Open Group 2017 PTHREAD_SETCANCELSTATE(3P)