Re: Clarification of pthread_cleanup_push() needed

[Florian Weimer <fw@deneb.enyo.de>]

* Richard Weinberger via Libc-help:

> But NPTL implements thread cancellation with signals, if I'm not
> completely mistaken the cleanup routine will run in signal context
> then.

Deferred cancellation only occurs in signal context if the
cancellation is acted upon from within a signal handler.  For the
signal handler case, whether cancellation handlers are restricted to
async-signal-safe function calls depends on the type of signal (some
are synchronous, not asynchronous) and what is interrupted by the
signal (for asynchronous signals).

Asynchronous cancellation has even more constraints than asynchronous
signal safety, but it is rarely used.