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Re: [Qemu-block] [PATCH 0/4] coroutine-lock: polymorphic CoQueue

From: Fam Zheng
Subject: Re: [Qemu-block] [PATCH 0/4] coroutine-lock: polymorphic CoQueue
Date: Tue, 16 Jan 2018 11:13:04 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0

On 01/16/2018 06:08 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).

Reviewed-by: Fam Zheng <address@hidden>

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