установить состояние отмены и тип (set cancelability state and type)
Имя (Name)
pthread_setcancelstate, pthread_setcanceltype - set cancelability
state and type
Синопсис (Synopsis)
#include <pthread.h>
int pthread_setcancelstate(int state, int *oldstate);
int pthread_setcanceltype(int type, int *oldtype);
Compile and link with -pthread.
Описание (Description)
The pthread_setcancelstate() sets the cancelability state of the
calling thread to the value given in state. The previous
cancelability state of the thread is returned in the buffer
pointed to by oldstate. The state argument must have one of the
following values:
PTHREAD_CANCEL_ENABLE
The thread is cancelable. This is the default
cancelability state in all new threads, including the
initial thread. The thread's cancelability type
determines when a cancelable thread will respond to a
cancellation request.
PTHREAD_CANCEL_DISABLE
The thread is not cancelable. If a cancellation request
is received, it is blocked until cancelability is enabled.
The pthread_setcanceltype() sets the cancelability type of the
calling thread to the value given in type. The previous
cancelability type of the thread is returned in the buffer
pointed to by oldtype. The type argument must have one of the
following values:
PTHREAD_CANCEL_DEFERRED
A cancellation request is deferred until the thread next
calls a function that is a cancellation point (see
pthreads(7)). This is the default cancelability type in
all new threads, including the initial thread.
Even with deferred cancellation, a cancellation point in
an asynchronous signal handler may still be acted upon and
the effect is as if it was an asynchronous cancellation.
PTHREAD_CANCEL_ASYNCHRONOUS
The thread can be canceled at any time. (Typically, it
will be canceled immediately upon receiving a cancellation
request, but the system doesn't guarantee this.)
The set-and-get operation performed by each of these functions is
atomic with respect to other threads in the process calling the
same function.
Возвращаемое значение (Return value)
On success, these functions return 0; on error, they return a
nonzero error number.
Ошибки (Error)
The pthread_setcancelstate() can fail with the following error:
EINVAL Invalid value for state.
The pthread_setcanceltype() can fail with the following error:
EINVAL Invalid value for type.
Атрибуты (Attributes)
For an explanation of the terms used in this section, see
attributes(7).
┌────────────────────────────────┬─────────────────────┬─────────┐
│Interface │ Attribute │ Value │
├────────────────────────────────┼─────────────────────┼─────────┤
│pthread_setcancelstate(), │ Thread safety │ MT-Safe │
│pthread_setcanceltype() │ │ │
├────────────────────────────────┼─────────────────────┼─────────┤
│pthread_setcancelstate(), │ Async-cancel safety │ AC-Safe │
│pthread_setcanceltype() │ │ │
└────────────────────────────────┴─────────────────────┴─────────┘
Стандарты (Conforming to)
POSIX.1-2001, POSIX.1-2008.
Примечание (Note)
For details of what happens when a thread is canceled, see
pthread_cancel(3).
Briefly disabling cancelability is useful if a thread performs
some critical action that must not be interrupted by a
cancellation request. Beware of disabling cancelability for long
periods, or around operations that may block for long periods,
since that will render the thread unresponsive to cancellation
requests.
Asynchronous cancelability
Setting the cancelability type to PTHREAD_CANCEL_ASYNCHRONOUS is
rarely useful. Since the thread could be canceled at any time,
it cannot safely reserve resources (e.g., allocating memory with
malloc(3)), acquire mutexes, semaphores, or locks, and so on.
Reserving resources is unsafe because the application has no way
of knowing what the state of these resources is when the thread
is canceled; that is, did cancellation occur before the resources
were reserved, while they were reserved, or after they were
released? Furthermore, some internal data structures (e.g., the
linked list of free blocks managed by the malloc(3) family of
functions) may be left in an inconsistent state if cancellation
occurs in the middle of the function call. Consequently, clean-
up handlers cease to be useful.
Functions that can be safely asynchronously canceled are called
async-cancel-safe functions. POSIX.1-2001 and POSIX.1-2008
require only that pthread_cancel(3), pthread_setcancelstate(),
and pthread_setcanceltype() be async-cancel-safe. In general,
other library functions can't be safely called from an
asynchronously cancelable thread.
One of the few circumstances in which asynchronous cancelability
is useful is for cancellation of a thread that is in a pure
compute-bound loop.
Portability notes
The Linux threading implementations permit the oldstate argument
of pthread_setcancelstate() to be NULL, in which case the
information about the previous cancelability state is not
returned to the caller. Many other implementations also permit a
NULL oldstat argument, but POSIX.1 does not specify this point,
so portable applications should always specify a non-NULL value
in oldstate. A precisely analogous set of statements applies for
the oldtype argument of pthread_setcanceltype().
Примеры (Examples)
See pthread_cancel(3).
Смотри также (See also)
pthread_cancel(3), pthread_cleanup_push(3),
pthread_testcancel(3), pthreads(7)
