int
pthread_setcancelstate(
int state
, int *oldstate
)
int
pthread_setcanceltype(
int type
, int *oldtype
)
void
pthread_testcancel(
void
)
)
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 referenced by
oldstate
.
Legal values for
state
are
PTHREAD_CANCEL_ENABLE
and
PTHREAD_CANCEL_DISABLE
.
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
PTHREAD_CANCEL_ASYNCHRONOUS
.
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 cancelability is disabled.
Each thread maintains its own ``cancelability state'' which may be encoded in two bits:
PTHREAD_CANCEL_DISABLE
,
cancellation requests against the target thread are held pending.
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 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.
),
close(
),
connect(
),
creat(
),
fcntl(
),
fsync(
),
fsync_range(
),
msgrcv(
),
msgsnd(
),
msync(
),
nanosleep(
),
open(
),
pause(
),
poll(
),
pread(
),
pselect(
),
pthread_cond_timedwait(
),
pthread_cond_wait(
),
pthread_join(
),
pthread_testcancel(
),
pwrite(
),
read(
),
readv(
),
recv(
),
recvfrom(
),
recvmsg(
),
select(
),
sem_timedwait(
),
sem_wait(
),
send(
),
sendmsg(
),
sendto(
),
sigpause(
),
sigsuspend(
),
sigtimedwait(
),
sigwait(
),
sigwaitinfo(
),
sleep(
),
system(
),
tcdrain(
),
usleep(
),
wait(
),
waitid(
),
waitpid(
),
write(
),
and
writev(
).
)
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 canceled.
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 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.
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 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.
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.
)
may fail with:
EINVAL
]
PTHREAD_CANCEL_ENABLE
or
PTHREAD_CANCEL_DISABLE
.
The function
pthread_setcanceltype()
may fail with:
EINVAL
]
PTHREAD_CANCEL_DEFERRED
or
PTHREAD_CANCEL_ASYNCHRONOUS
.
)
conforms to
ISO/IEC 9945-1:1996 (``POSIX.1'') .