On Fri, Dec 08, 2017 at 02:02:32PM -0600, Eric Blake wrote:
> On 12/08/2017 12:12 PM, Paolo Bonzini wrote:
> > On 08/12/2017 16:13, Stefan Hajnoczi wrote:
> >>> - qemu_mutex_lock(&pool->lock);
> >>> + QEMU_LOCK_GUARD(QemuMutex, pool_guard, &pool->lock);
> >>> if (pool->idle_threads == 0 && pool->cur_threads <
> >>> pool->max_threads) {
> >>> spawn_thread(pool);
> >>> }
> >>> QTAILQ_INSERT_TAIL(&pool->request_list, req, reqs);
> >>> - qemu_mutex_unlock(&pool->lock);
> >>> + qemu_lock_guard_unlock(&pool_guard);
> >> Why not QEMU_WITH_LOCK()? Then you can get rid of the explicit unlock.
> >
> > I agree that QEMU_WITH_LOCK_GUARD is better in this case. (IIRC I wrote
> > this patch before coming up with the is_taken trick!).
> >
> > My main question for the series is what you think the balance should be
> > between a more widely applicable API and a simpler one.
>
> If you require the user to provide the scope, this could be:
>
> @@ -258,12 +254,12 @@ BlockAIOCB *thread_pool_submit_aio(ThreadPool *pool,
>
> trace_thread_pool_submit(pool, req, arg);
>
> - qemu_mutex_lock(&pool->lock);
> - if (pool->idle_threads == 0 && pool->cur_threads < pool->max_threads) {
> - spawn_thread(pool);
> - QTAILQ_INSERT_TAIL(&pool->request_list, req, reqs);
> + {
> + QEMU_LOCK_GUARD(QemuMutex, pool_guard, &pool->lock);
> + if (pool->idle_threads == 0 && pool->cur_threads <
> pool->max_threads) {
> + spawn_thread(pool);
> + }
> + QTAILQ_INSERT_TAIL(&pool->request_list, req, reqs);
> }
> - qemu_mutex_unlock(&pool->lock);
> qemu_sem_post(&pool->sem);
> return &req->common;
> }
>
> In other words, I don't see what 'QEMU_WITH_LOCK_GUARD() {}' buys us
> over '{ QEMU_LOCK_GUARD() }'.
The QEMU_WITH_LOCK_GUARD() {} syntax is nice because it's similar to
if/while/for statements.
However, { QEMU_LOCK_GUARD() } doesn't hide a for statement in a macro
so the break statement works inside the scope. Less chance of bugs.
I'd be okay without QEMU_WITH_LOCK_GUARD().
Stefan
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