установить состояние отмены (set cancelability state)
Пролог (Prolog)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
Имя (Name)
pthread_setcancelstate, pthread_setcanceltype, pthread_testcancel
— set cancelability state
Синопсис (Synopsis)
#include <pthread.h>
int pthread_setcancelstate(int state, int *oldstate);
int pthread_setcanceltype(int type, int *oldtype);
void pthread_testcancel(void);
Описание (Description)
The pthread_setcancelstate() function shall atomically both set
the calling thread's cancelability state to the indicated state
and return 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 shall atomically both set
the calling thread's cancelability type to the indicated type and
return 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, shall be
PTHREAD_CANCEL_ENABLE and PTHREAD_CANCEL_DEFERRED respectively.
The pthread_testcancel() function shall create a cancellation
point in the calling thread. The pthread_testcancel() function
shall have no effect if cancelability is disabled.
Возвращаемое значение (Return value)
If successful, the pthread_setcancelstate() and
pthread_setcanceltype() functions shall return zero; otherwise,
an error number shall be returned to indicate the error.
Ошибки (Error)
The pthread_setcancelstate() function may fail if:
EINVAL The specified state is not PTHREAD_CANCEL_ENABLE or
PTHREAD_CANCEL_DISABLE.
The pthread_setcanceltype() function may fail if:
EINVAL The specified type is not PTHREAD_CANCEL_DEFERRED or
PTHREAD_CANCEL_ASYNCHRONOUS.
These functions shall not return an error code of [EINTR].
The following sections are informative.
Примеры (Examples)
None.
Использование в приложениях (Application usage)
In order to write a signal handler for an asynchronous signal
which can run safely in a cancellable thread,
pthread_setcancelstate() must be used to disable cancellation for
the duration of any calls that the signal handler makes which are
cancellation points. However, the standard does not permit
strictly conforming applications to call pthread_setcancelstate()
from a signal handler since it is not currently required to be
async-signal-safe. On implementations where
pthread_setcancelstate() is not async-signal-safe, alternatives
are to ensure either that the corresponding signals are blocked
during execution of functions that are not async-cancel-safe or
that cancellation is disabled during times when those signals
could be delivered. Implementations are strongly encouraged to
make pthread_setcancelstate() async-signal-safe.
Обоснование (Rationale)
The pthread_setcancelstate() and pthread_setcanceltype()
functions control the points at which a thread may be
asynchronously canceled. For cancellation control to be usable in
modular fashion, some rules need to be followed.
An object can be considered 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 does not want to
be concerned about cleaning 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 is 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 the 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.
Будущие направления (Future directions)
The pthread_setcancelstate() function may be added to the table
of async-signal-safe functions in Section 2.4.3, Signal Actions.
Смотри также (See also)
pthread_cancel(3p)
The Base Definitions volume of POSIX.1‐2017, pthread.h(0p)
