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
149 .It Fn sem_clockwait_np
173 .Fn pthread_setcancelstate
175 .Fn pthread_setcanceltype
176 functions are used to control the points at which a thread may be
177 asynchronously canceled.
178 For cancellation control to be usable in modular
179 fashion, some rules must be followed.
181 For purposes of this discussion, consider an object to be a generalization
183 It is a set of procedures and global variables written as
184 a unit and called by clients not known by the object.
188 First, cancelability should only be disabled on entry to an object, never
190 On exit from an object, the cancelability state should
191 always be restored to its value on entry to the object.
193 This follows from a modularity argument: if the client of an object (or the
194 client of an object that uses that object) has disabled cancelability, it is
195 because the client does not want to have to worry about how to clean up if the
196 thread is canceled while executing some sequence of actions.
198 is called in such a state and it enables cancelability and a cancellation
199 request is pending for that thread, then the thread will be canceled,
200 contrary to the wish of the client that disabled.
202 Second, the cancelability type may be explicitly set to either
206 upon entry to an object.
207 But as with the cancelability state, on exit from
208 an object that cancelability type should always be restored to its value on
211 Finally, only functions that are cancel-safe may be called from a thread that
212 is asynchronously cancelable.
215 .Fn pthread_setcancelstate
217 .Fn pthread_setcanceltype
218 functions will return zero.
219 Otherwise, an error number shall be returned to
223 .Fn pthread_setcancelstate
227 The specified state is not
228 .Dv PTHREAD_CANCEL_ENABLE
230 .Dv PTHREAD_CANCEL_DISABLE .
234 .Fn pthread_setcanceltype
238 The specified state is not
239 .Dv PTHREAD_CANCEL_DEFERRED
241 .Dv PTHREAD_CANCEL_ASYNCHRONOUS .
247 .Fn pthread_testcancel
250 The standard allows implementations to make many more functions
253 This manual page was written by
254 .An David Leonard Aq Mt d@openbsd.org
258 .Xr pthread_cancel 3 .