What are pthread cancelation points used for?

Question

There is discussion of pthread cancellation points (http://man7.org/linux/man-pages/man3/pthread_cancel.3.html) on several question. In some cases the respondents say that c

Answer 1

... what are pthread cancellation points used for?

From man 7 pthreads:

Cancellation points

POSIX.1 specifies that certain functions must, and certain other functions may, be cancellation points.

More:

If a thread is cancelable, its cancelability type is deferred, and a cancellation request is pending for the thread, then the thread is canceled when it calls a function that is a cancellation point.

Referring the questions:

1. The API functions defined by POSIX here: http://man7.org/linux/man-pages/man7/pthreads.7.html (Cancellation Points) either are cancellations points or may be some.
2. To introduce a (user-) specific cancellation point call pthread_testcancel() where you feel it might be necessary.
3. No.
4. They are defined by POSIX to provide a standardise way to handle the way cancellation might happen. This especially makes sense for blocking functions.
5. see 2.

As a final note: Avoid cancellation of threads whereever possible, as it might lead to unexpected and unreproducable behaviour of a program. Try to always design a program to be able to gracefully shut it down by ending all threads without explicit calling pthread_cancel().