pthread_setcancelstate() pthread_setcanceltype() pthread_testcancel()

NAME

pthread_setcancelstate, pthread_setcanceltype, pthread_testcancel - set cancelability state

这三个函数用来设置线程是否可以被其他线程调用pthread_cancel函数取消/终止。

SYNOPSIS 概要

#include <pthread.h>

int pthread_setcancelstate(int state, int *oldstate);

int pthread_setcanceltype(int type, int *oldtype);

void pthread_testcancel(void);

DESCRIPTION 描述

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.

译文：pthread_setcancelstate()函数用来设置当前线程的“可取消性”状态，并且将先前的状态返回到oldstate引用中。

“可取消性”状态的合法值分别是：PTHREAD_CANCEL_ENABLE 和 PTHREAD_CANCEL_DISABLE。

这个函数还可以查询当前线程的“可取消性”状态，即把第一个参数设为NULL。

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.

译文：pthread_setcanceltype() 函数用来设置当前线程的“可取消类型”，并且将先前的类型返回到oldtype引用中。

“可取消类型”的合法值分别是：

PTHREAD_CANCEL_DEFERRED ：线程接收到取消操作后，直到运行到“可取消点”后取消。

PTHREAD_CANCEL_ASYNCHRONOUS ：线程接收到取消操作后，立即取消。

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.

译文：“可取消性”和“可取消类型”存在于任意一个新建线程中，包括主线程，默认设置是PTHREAD_CANCEL_ENABLE 和 PTHREAD_CANCEL_DEFERRED。

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.

译文：pthread_testcancel()函数用来在当前线程创建一个“可取消点”。如果当前线程是不能取消的，则这个函数无效。

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.

ERRORS

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.

EXAMPLES

None.

APPLICATION USAGE

None.

RATIONALE 基本原理

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.

FUTURE DIRECTIONS

None.

SEE ALSO

pthread_cancel

XBD
<pthread.h>

CHANGE HISTORY

First released in Issue 5. Included for alignment with the POSIX Threads Extension.

Issue 6

The pthread_setcancelstate(), pthread_setcanceltype(), and
pthread_testcancel() functions are marked as part of the Threads option.

Issue 7

The pthread_setcancelstate(), pthread_setcanceltype(), and
pthread_testcancel() functions are moved from the Threads option to the Base.