Re: [Qemu-devel] [PATCH v3 0/5] coroutine-lock: polymorphic CoQueue

[Eric Blake]

On 01/25/2018 11:59 AM, Paolo Bonzini wrote:
> There are cases in which a queued coroutine must be restarted from
> non-coroutine context (with qemu_co_enter_next).  In this cases,
> qemu_co_enter_next also needs to be thread-safe, but it cannot use a
> CoMutex and so cannot qemu_co_queue_wait.  This happens in curl (which
> right now is rolling its own list of Coroutines) and will happen in
> Fam's NVMe driver as well.
> 
> This series extracts the idea of a polymorphic lockable object
> from my "scoped lock guard" proposal, and applies it to CoQueue.
> The implementation of QemuLockable is similar to C11 _Generic, but
> redone using the preprocessor and GCC builtins for compatibility.
> 
> In general, while a bit on the esoteric side, the functionality used
> to emulate _Generic is fairly old in GCC, and the builtins are already
> used by include/qemu/atomic.h; the series was tested with Fedora 27 (boot
> Damn Small Linux via http) and CentOS 6 (compiled only).
> 
> Paolo
> 
> v1->v2: fix typos and copyright year
> 
> v2->v3: add tests, fix brown paper bag bug, avoid -Waddress errors

I spotted a few typos, but did not rigorously test it enough to leave
R-b.  At any rate, writing polymorphic code in C is an interesting
exercise, so it was fun learning from this thread.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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