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 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.
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.
Each thread maintains its own “cancelability state” which may be encoded in two bits:
Cancelability Enable
When cancelability is PTHREAD_CANCEL_DISABLE, cancellation 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 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.
Cancellation Points
Cancellation points will occur when a thread is executing the following functions: accept(), aio_suspend(), clock_nanosleep(), close(), connect(), creat(), fcntl(), fdatasync(), fsync(), fsync_range(), kevent(), mq_receive(), mq_send(), mq_timedreceive(), mq_timedsend(), msgrcv(), msgsnd(), msync(), nanosleep(), open(), pause(), poll(), pollts(), 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(), wait4(), waitid(), waitpid(), write(), and writev().