3 .Dt PTHREAD_TESTCANCEL 3
6 .Nm pthread_setcancelstate ,
7 .Nm pthread_setcanceltype ,
9 .Nd set cancelability state
15 .Fn pthread_setcancelstate "int state" "int *oldstate"
17 .Fn pthread_setcanceltype "int type" "int *oldtype"
19 .Fn pthread_testcancel "void"
22 .Fn pthread_setcancelstate
23 function atomically both sets the calling thread's cancelability state
30 returns the previous cancelability state at the location referenced by
35 .Dv PTHREAD_CANCEL_ENABLE
37 .Dv PTHREAD_CANCEL_DISABLE .
40 .Fn pthread_setcanceltype
41 function atomically both sets the calling thread's cancelability type
48 returns the previous cancelability type at the location referenced by
53 .Dv PTHREAD_CANCEL_DEFERRED
55 .Dv PTHREAD_CANCEL_ASYNCHRONOUS .
57 The cancelability state and type of any newly created threads, including the
60 was first invoked, are
61 .Dv PTHREAD_CANCEL_ENABLE
63 .Dv PTHREAD_CANCEL_DEFERRED
67 .Fn pthread_testcancel
68 function creates a cancellation point in the calling thread.
70 .Fn pthread_testcancel
71 function has no effect if cancelability is disabled.
73 .Ss Cancelability States
74 The cancelability state of a thread determines the action taken upon
75 receipt of a cancellation request.
76 The thread may control cancellation in
79 Each thread maintains its own
80 .Dq cancelability state
81 which may be encoded in two bits:
83 .It Em Cancelability Enable
85 .Dv PTHREAD_CANCEL_DISABLE ,
86 cancellation requests against the target thread are held pending.
87 .It Em Cancelability Type
88 When cancelability is enabled and the cancelability type is
89 .Dv PTHREAD_CANCEL_ASYNCHRONOUS ,
90 new or pending cancellation requests may be acted upon at any time.
91 When cancelability is enabled and the cancelability type is
92 .Dv PTHREAD_CANCEL_DEFERRED ,
93 cancellation requests are held pending until a cancellation point (see
95 If cancelability is disabled, the setting of the
96 cancelability type has no immediate effect as all cancellation requests
97 are held pending; however, once cancelability is enabled again the new
98 type will be in effect.
100 .Ss Cancellation Points
101 Cancellation points will occur when a thread is executing the following
103 .Bl -tag -width "Fn pthread_cond_timedwait" -compact
113 function is a cancellation point if
122 function is a cancellation point if it is potentially blocking,
125 argument is non-zero.
128 .It Fn mq_timedreceive
138 .It Fn pthread_cond_timedwait
139 .It Fn pthread_cond_wait
141 .It Fn pthread_testcancel
172 .Fn pthread_setcancelstate
174 .Fn pthread_setcanceltype
175 functions are used to control the points at which a thread may be
176 asynchronously canceled.
177 For cancellation control to be usable in modular
178 fashion, some rules must be followed.
180 For purposes of this discussion, consider an object to be a generalization
182 It is a set of procedures and global variables written as
183 a unit and called by clients not known by the object.
187 First, cancelability should only be disabled on entry to an object, never
189 On exit from an object, the cancelability state should
190 always be restored to its value on entry to the object.
192 This follows from a modularity argument: if the client of an object (or the
193 client of an object that uses that object) has disabled cancelability, it is
194 because the client does not want to have to worry about how to clean up if the
195 thread is canceled while executing some sequence of actions.
197 is called in such a state and it enables cancelability and a cancellation
198 request is pending for that thread, then the thread will be canceled,
199 contrary to the wish of the client that disabled.
201 Second, the cancelability type may be explicitly set to either
205 upon entry to an object.
206 But as with the cancelability state, on exit from
207 an object that cancelability type should always be restored to its value on
210 Finally, only functions that are cancel-safe may be called from a thread that
211 is asynchronously cancelable.
214 .Fn pthread_setcancelstate
216 .Fn pthread_setcanceltype
217 functions will return zero.
218 Otherwise, an error number shall be returned to
222 .Fn pthread_setcancelstate
226 The specified state is not
227 .Dv PTHREAD_CANCEL_ENABLE
229 .Dv PTHREAD_CANCEL_DISABLE .
233 .Fn pthread_setcanceltype
237 The specified state is not
238 .Dv PTHREAD_CANCEL_DEFERRED
240 .Dv PTHREAD_CANCEL_ASYNCHRONOUS .
246 .Fn pthread_testcancel
249 The standard allows implementations to make many more functions
252 This manual page was written by
253 .An David Leonard Aq Mt d@openbsd.org
257 .Xr pthread_cancel 3 .