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\" $FreeBSD: src/lib/libpthread/man/pthread_testcancel.3,v 1.9 2002/09/16 19:29:29 mini Exp $
Dd August 6, 2010
Dt PTHREAD_TESTCANCEL 3
Os
Sh NAME
Nm pthread_setcancelstate ,
Nm pthread_setcanceltype ,
Nm pthread_testcancel
Nd set cancelability state
Sh LIBRARY
Lb libpthread
Sh SYNOPSIS
In pthread.h
Ft int
Fn pthread_setcancelstate "int state" "int *oldstate"
Ft int
Fn pthread_setcanceltype "int type" "int *oldtype"
Ft void
Fn pthread_testcancel "void"
Sh DESCRIPTION
The
Fn pthread_setcancelstate
function atomically both sets the calling thread's cancelability state
to the indicated
Fa state
and, if
Fa oldstate
is not
Dv NULL ,
returns the previous cancelability state at the location referenced by
Fa oldstate .
Legal values for
Fa state
are
Dv PTHREAD_CANCEL_ENABLE
and
Dv PTHREAD_CANCEL_DISABLE .
Pp
The
Fn pthread_setcanceltype
function atomically both sets the calling thread's cancelability type
to the indicated
Fa type
and, if
Fa oldtype
is not
Dv NULL ,
returns the previous cancelability type at the location referenced by
Fa oldtype .
Legal values for
Fa type
are
Dv PTHREAD_CANCEL_DEFERRED
and
Dv PTHREAD_CANCEL_ASYNCHRONOUS .
Pp
The cancelability state and type of any newly created threads, including the
thread in which
Fn main
was first invoked, are
Dv PTHREAD_CANCEL_ENABLE
and
Dv PTHREAD_CANCEL_DEFERRED
respectively.
Pp
The
Fn pthread_testcancel
function creates a cancellation point in the calling thread.
The
Fn pthread_testcancel
function has no effect if cancelability is disabled.
Ss Cancelability States
The cancelability state of a thread determines the action taken upon
receipt of a cancellation request.
The thread may control cancellation in
a number of ways.
Pp
Each thread maintains its own
Dq cancelability state
which may be encoded in two bits:
Bl -hang
It Em Cancelability Enable :
When cancelability is
Dv PTHREAD_CANCEL_DISABLE ,
cancellation requests against the target thread are held pending.
It Em Cancelability Type :
When cancelability is enabled and the cancelability type is
Dv PTHREAD_CANCEL_ASYNCHRONOUS ,
new or pending cancellation requests may be acted upon at any time.
When cancelability is enabled and the cancelability type is
Dv PTHREAD_CANCEL_DEFERRED ,
cancellation requests are held pending until a cancellation point (see
below) is reached.
If cancelability is disabled, the setting of the
cancelability type has no immediate effect as all cancellation requests
are held pending; however, once cancelability is enabled again the new
type will be in effect.
El
Ss Cancellation Points
Cancellation points will occur when a thread is executing the following
functions:
Fn accept ,
Fn aio_suspend ,
Fn clock_nanosleep ,
Fn close ,
Fn connect ,
Fn creat ,
Fn fcntl ,
Fn fdatasync ,
Fn fsync ,
Fn fsync_range ,
\".Fn getmsg ,
\".Fn getpmsg ,
Fn kevent ,
\".Fn lockf ,
Fn mq_receive ,
Fn mq_send ,
Fn mq_timedreceive ,
Fn mq_timedsend ,
Fn msgrcv ,
Fn msgsnd ,
Fn msync ,
Fn nanosleep ,
Fn open ,
Fn pause ,
Fn poll ,
Fn pollts ,
Fn pread ,
Fn pselect ,
Fn pthread_cond_timedwait ,
Fn pthread_cond_wait ,
Fn pthread_join ,
Fn pthread_testcancel ,
\".Fn putmsg ,
\".Fn putpmsg ,
Fn pwrite ,
Fn read ,
Fn readv ,
Fn recv ,
Fn recvfrom ,
Fn recvmsg ,
Fn select ,
Fn sem_timedwait ,
Fn sem_wait ,
Fn send ,
Fn sendmsg ,
Fn sendto ,
Fn sigpause ,
Fn sigsuspend ,
Fn sigtimedwait ,
Fn sigwait ,
Fn sigwaitinfo ,
Fn sleep ,
Fn system ,
Fn tcdrain ,
Fn usleep ,
Fn wait ,
Fn wait4 ,
Fn waitid ,
Fn waitpid ,
Fn write ,
and
Fn writev .
Sh RETURN VALUES
If successful, the
Fn pthread_setcancelstate
and
Fn pthread_setcanceltype
functions will return zero.
Otherwise, an error number shall be returned to
indicate the error.
Pp
The
Fn pthread_setcancelstate
and
Fn pthread_setcanceltype
functions are used to control the points at which a thread may be
asynchronously canceled.
For cancellation control to be usable in modular
fashion, some rules must be followed.
Pp
For purposes of this discussion, consider an object to be a generalization
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.
Pp
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.
Pp
This follows from a modularity argument: if the client of an object (or the
client of an object that uses that object) has disabled cancelability, it is
because the client doesn't want to have to worry about how to clean up if the
thread is canceled while executing some sequence of actions.
If an object
is called in such a state and it enables cancelability and a cancellation
request is pending for that thread, then the thread will be canceled,
contrary to the wish of the client that disabled.
Pp
Second, the cancelability type may be explicitly set to either
Em deferred
or
Em 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.
Pp
Finally, only functions that are cancel-safe may be called from a thread that
is asynchronously cancelable.
Sh ERRORS
The function
Fn pthread_setcancelstate
may fail with:
Bl -tag -width Er
It Bq Er EINVAL
The specified state is not
Dv PTHREAD_CANCEL_ENABLE
or
Dv PTHREAD_CANCEL_DISABLE .
El
Pp
The function
Fn pthread_setcanceltype
may fail with:
Bl -tag -width Er
It Bq Er EINVAL
The specified state is not
Dv PTHREAD_CANCEL_DEFERRED
or
Dv PTHREAD_CANCEL_ASYNCHRONOUS .
El
Sh SEE ALSO
Xr pthread_cancel 3
Sh STANDARDS
These functions conform to
St -p1003.1-2001 .
Sh AUTHORS
This man page was written by
An David Leonard Aq Mt [email protected]
for the
Ox
implementation of
Xr pthread_cancel 3 .

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