qemu/tests/iothread.c
Paolo Bonzini 0c330a734b aio: introduce aio_co_schedule and aio_co_wake
aio_co_wake provides the infrastructure to start a coroutine on a "home"
AioContext.  It will be used by CoMutex and CoQueue, so that coroutines
don't jump from one context to another when they go to sleep on a
mutex or waitqueue.  However, it can also be used as a more efficient
alternative to one-shot bottom halves, and saves the effort of tracking
which AioContext a coroutine is running on.

aio_co_schedule is the part of aio_co_wake that starts a coroutine
on a remove AioContext, but it is also useful to implement e.g.
bdrv_set_aio_context callbacks.

The implementation of aio_co_schedule is based on a lock-free
multiple-producer, single-consumer queue.  The multiple producers use
cmpxchg to add to a LIFO stack.  The consumer (a per-AioContext bottom
half) grabs all items added so far, inverts the list to make it FIFO,
and goes through it one item at a time until it's empty.  The data
structure was inspired by OSv, which uses it in the very code we'll
"port" to QEMU for the thread-safe CoMutex.

Most of the new code is really tests.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Message-id: 20170213135235.12274-3-pbonzini@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2017-02-21 11:14:07 +00:00

92 lines
2.2 KiB
C

/*
* Event loop thread implementation for unit tests
*
* Copyright Red Hat Inc., 2013, 2016
*
* Authors:
* Stefan Hajnoczi <stefanha@redhat.com>
* Paolo Bonzini <pbonzini@redhat.com>
*
* This work is licensed under the terms of the GNU GPL, version 2 or later.
* See the COPYING file in the top-level directory.
*
*/
#include "qemu/osdep.h"
#include "qapi/error.h"
#include "block/aio.h"
#include "qemu/main-loop.h"
#include "qemu/rcu.h"
#include "iothread.h"
struct IOThread {
AioContext *ctx;
QemuThread thread;
QemuMutex init_done_lock;
QemuCond init_done_cond; /* is thread initialization done? */
bool stopping;
};
static __thread IOThread *my_iothread;
AioContext *qemu_get_current_aio_context(void)
{
return my_iothread ? my_iothread->ctx : qemu_get_aio_context();
}
static void *iothread_run(void *opaque)
{
IOThread *iothread = opaque;
rcu_register_thread();
my_iothread = iothread;
qemu_mutex_lock(&iothread->init_done_lock);
iothread->ctx = aio_context_new(&error_abort);
qemu_cond_signal(&iothread->init_done_cond);
qemu_mutex_unlock(&iothread->init_done_lock);
while (!atomic_read(&iothread->stopping)) {
aio_poll(iothread->ctx, true);
}
rcu_unregister_thread();
return NULL;
}
void iothread_join(IOThread *iothread)
{
iothread->stopping = true;
aio_notify(iothread->ctx);
qemu_thread_join(&iothread->thread);
qemu_cond_destroy(&iothread->init_done_cond);
qemu_mutex_destroy(&iothread->init_done_lock);
aio_context_unref(iothread->ctx);
g_free(iothread);
}
IOThread *iothread_new(void)
{
IOThread *iothread = g_new0(IOThread, 1);
qemu_mutex_init(&iothread->init_done_lock);
qemu_cond_init(&iothread->init_done_cond);
qemu_thread_create(&iothread->thread, NULL, iothread_run,
iothread, QEMU_THREAD_JOINABLE);
/* Wait for initialization to complete */
qemu_mutex_lock(&iothread->init_done_lock);
while (iothread->ctx == NULL) {
qemu_cond_wait(&iothread->init_done_cond,
&iothread->init_done_lock);
}
qemu_mutex_unlock(&iothread->init_done_lock);
return iothread;
}
AioContext *iothread_get_aio_context(IOThread *iothread)
{
return iothread->ctx;
}