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Re: Design hole in nptl (and more general in POSIX threads)



Jim Blandy wrote:
> Using __thread variables is async-safe.

Are you sure?  I'd expect them to be async-signal-unsafe if there is
dynamic lazy resolution of __thread storage blocks, and you haven't
accessed that variable in that thread yet.  In your example you have
accessed it, obviously.

In principle I'd expect the compiler to use pthread_key_getspecific()
or some similar low level libc routine to access variables declared in
that way although I don't know if any actually do that.

> pthread_self (which isn't officially async-signal-safe, but geez)

On some implementations pthread_self has to search a data structure
which is modified and hence locked whenever threads are created or
destroyed.  It's not surprising that it's not async-signal-safe.  I
think an older version of Glibc threads was like this on some
architectures.

-- Jamie




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