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

[Jamie Lokier <jamie shareable org>]

Dragi?a Duri? wrote:
> Advanced (probably every) garbage collector needs to scan threads stacks
> for pointers to traced heap being kept in local variable spaces of
> procedures in suspended threads. While suspending of other threads is
> possible in portable way (thanks to this list for help) it is not
> possible, in portable way, to get exact position of active portion of
> threads stack. Only way (I know of) goes through pthread_getattr_np()
> call which gives only partial information - one needs stack pointer
> (obtainable only through oh-so-portable pthread debug interface and only
> after hacking deeply nested include files for exact info on position of
> stack pointer in greglist structure.

You can send a signal such as SIGUSR1 to all threads and have them
record the stack pointer in a data structure before putting themselves
to sleep.

> Meaning, it is not possible to implement this fundamental feature of
> advanced high-level langugages in portable way.
>
> Are there plans to fix this somewhere before greglist? :)

Well, no matter what changes are made to nptl, it's not going to make
the solution portable to non-nptl platforms is it?

-- Jamie