Re: [Qemu-devel] [PATCH] coroutine: always use pooling

[Paolo Bonzini <pbonzini@redhat.com>]

Il 26/09/2012 16:34, Peter Maydell ha scritto:
>> It makes sense to use it for other implementations than ucontext, too.
>> >  Coroutine *qemu_coroutine_create(CoroutineEntry *entry)
>> >  {
>> > -    Coroutine *co = qemu_coroutine_new();
>> > +    Coroutine *co;
>> > +
>> > +    co = QSLIST_FIRST(&pool);
>> > +    if (co) {
>> > +        QSLIST_REMOVE_HEAD(&pool, pool_next);
>> > +        pool_size--;
>> > +    } else {
>> > +        co = qemu_coroutine_new();
>> > +    }
>> >      co->entry = entry;
>> >      return co;
>> >  }
> Since this is obviously going to blow up badly if it's called
> from multiple threads, is there some kind of assert we can add
> so that we fail obviously if somebody makes that coding error?
> [the difficulty is probably when your backend is the gthread
> one, at least I assume creating a coroutine inside a coroutine
> is allowed.]

Yes, it is; however, creating a coroutine outside the big QEMU lock is
not allowed.  Since one coroutine only runs at a time the code is safe,
just like the other global variables that are used in
qemu-coroutine-lock.c for example.

Paolo