Re: Go patch committed: Multiplex goroutines onto OS threads

[Ian Lance Taylor <iant at google dot com>]

Paolo Bonzini <bonzini@gnu.org> writes:

> On 11/28/2011 06:46 AM, Ian Lance Taylor wrote:
>> This implementation relies on the functions getcontext, setcontext, and
>> makecontext.  If there are systems which don't have those, getcontext
>> and setcontext can be replaced by setjmp and longjmp, but there is no
>> obvious replacement for makecontext.  I think that will have to be
>> implemented using processor-specific code, as it needs to set the stack
>> pointer to point to a new stack, and I don't know how to do that in a
>> portable processor-independent manner without using makecontext.
>
> ARM glibc does not implement these functions, so we have the same
> problem in QEMU.  (On top of this, there is no way that alternate
> stacks can work on OpenBSD, so we still have one coroutine per
> thread).

The other Go compiler already supports OpenBSD, so it must be possible
in some sense.


> For QEMU, I tried replacing for makecontext using sigaltstack.  It
> works on Linux but it needs a dedicated signal, so it is likely
> inappropriate for libgo.  It would also need to be tested across many
> operating systems because it may trigger subtleties in other OSes.

I don't have any problem using a dedicated signal.  That's an
interesting approach.  I wonder what the relative performance would be.

Anyhow, makecontext is easy to write in a system specific manner.  It
doesn't even have to be written in assembler, though getcontext and
setcontext do have to be assembler.  Why not just implement them for
ARM?

Ian