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     pthread_setcancelstate, pthread_setcanceltype, pthread_testcancel -- set
     cancelability state

     #include <pthread.h>

     pthread_setcancelstate(int	state, int *oldstate);

     pthread_setcanceltype(int type, int *oldtype);


     The pthread_setcancelstate() function atomically both sets	the calling
     thread's cancelability state to the indicated state and, if oldstate is
     not NULL, returns the previous cancelability state	at the location	refer-
     enced by oldstate.	 Legal values for state	are PTHREAD_CANCEL_ENABLE and

     The pthread_setcanceltype() function atomically both sets the calling
     thread's cancelability type to the	indicated type and, if oldtype is not
     NULL, returns the previous	cancelability type at the location referenced
     by	oldtype.  Legal	values for type	are PTHREAD_CANCEL_DEFERRED and

     The cancelability state and type of any newly created threads, including
     the thread	in which main()	was first invoked, are PTHREAD_CANCEL_ENABLE
     and PTHREAD_CANCEL_DEFERRED respectively.

     The pthread_testcancel() function creates a cancellation point in the
     calling thread.  The pthread_testcancel() function	has no effect if can-
     celability	is disabled.

   Cancelability States
     The cancelability state of	a thread determines the	action taken upon re-
     ceipt of a	cancellation request.  The thread may control cancellation in
     a number of ways.

     Each thread maintains its own "cancelability state" which may be encoded
     in	two bits:

     Cancelability Enable When cancelability is	PTHREAD_CANCEL_DISABLE,	can-
	     cellation requests	against	the target thread are held pending.

     Cancelability Type	When cancelability is enabled and the cancelability
	     type is PTHREAD_CANCEL_ASYNCHRONOUS, new or pending cancellation
	     requests may be acted upon	at any time.  When cancelability is
	     enabled and the cancelability type	is PTHREAD_CANCEL_DEFERRED,
	     cancellation requests are held pending until a cancellation point
	     (see below) is reached.  If cancelability is disabled, the	set-
	     ting of the cancelability type has	no immediate effect as all
	     cancellation requests are held pending; however, once cancelabil-
	     ity is enabled again the new type will be in effect.

   Cancellation	Points
     Cancellation points will occur when a thread is executing the following
     base interfaces: accept(),	close(), connect(), creat(), fcntl(F_SETLKW),
     fdatasync(), fsync(), lockf(), msgrcv(), msgsnd(),	msync(), nanosleep(),
     open(), openat(), pause(),	poll(),	pread(), pthread_cond_timedwait(),
     pthread_cond_wait(), pthread_join(), pthread_testcancel(),	pwrite(),
     read(), readv(), recv(), recvfrom(), recvmsg(), select(),
     sem_timedwait(), sem_wait(), send(), sendmsg(), sendto(), sigsuspend(),
     sigwait(),	sleep(), system(), tcdrain(), wait(), waitpid(), write(),

     In	addition, cancellation points will occur when a	thread is executing
     the following extension interfaces: accept4(), closefrom(), ppoll(),
     preadv(), pwritev(), wait3(), wait4().

     If	successful, the	pthread_setcancelstate() and pthread_setcanceltype()
     functions will return zero.  Otherwise, an	error number shall be returned
     to	indicate the error.

     The pthread_setcancelstate() and pthread_setcanceltype() functions	are
     used to control the points	at which a thread may be asynchronously	can-
     celled.  For cancellation control to be usable in modular fashion,	some
     rules must	be followed.

     For purposes of this discussion, consider an object to be a generaliza-
     tion of a procedure.  It is a set of procedures and global	variables
     written as	a unit and called by clients not known by the object.  Objects
     may depend	on other objects.

     First, cancelability should only be disabled on entry to an object, never
     explicitly	enabled.  On exit from an object, the cancelability state
     should always be restored to its value on entry to	the object.

     This follows from a modularity argument: if the client of an object (or
     the client	of an object that uses that object) has	disabled cancelabil-
     ity, it is	because	the client doesn't want	to have	to worry about how to
     clean up if the thread is cancelled while executing some sequence of ac-
     tions.  If	an object is called in such a state and	it enables cancelabil-
     ity and a cancellation request is pending for that	thread,	then the
     thread will be cancelled, contrary	to the wish of the client that dis-

     Second, the cancelability type may	be explicitly set to either deferred
     or	asynchronous upon entry	to an object.  But as with the cancelability
     state, on exit from an object that	cancelability type should always be
     restored to its value on entry to the object.

     Finally, only functions that are cancel-safe may be called	from a thread
     that is asynchronously cancelable.

     The function pthread_setcancelstate() may fail with:

     [EINVAL]		The specified state is not PTHREAD_CANCEL_ENABLE or

     The function pthread_setcanceltype() may fail with:

     [EINVAL]		The specified state is not PTHREAD_CANCEL_DEFERRED or


     pthread_testcancel() conforms to ISO/IEC 9945-1:1996 ("POSIX.1")

FreeBSD	13.0			August 31, 2014			  FreeBSD 13.0


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