qemu/qemu-coroutine-lock.c
Stefan Hajnoczi 28f0824696 coroutine: use AioContext for CoQueue BH
CoQueue uses a BH to awake coroutines that were made ready to run again
using qemu_co_queue_next() or qemu_co_queue_restart_all().  The BH
currently runs in the iothread AioContext and would break coroutines
that run in a different AioContext.

This is a slightly tricky problem because the lifetime of the BH exceeds
that of the CoQueue.  This means coroutines can be awoken after CoQueue
itself has been freed.  Also, there is no qemu_co_queue_destroy()
function which we could use to handle freeing resources.

Introducing qemu_co_queue_destroy() has a ripple effect of requiring us
to also add qemu_co_mutex_destroy() and qemu_co_rwlock_destroy(), as
well as updating all callers.  Avoid doing that.

We also cannot switch from BH to GIdle function because aio_poll() does
not dispatch GIdle functions.  (GIdle functions make memory management
slightly easier because they free themselves.)

Finally, I don't want to move unlock_queue and unlock_bh into
AioContext.  That would break encapsulation - AioContext isn't supposed
to know about CoQueue.

This patch implements a different solution: each qemu_co_queue_next() or
qemu_co_queue_restart_all() call creates a new BH and list of coroutines
to wake up.  Callers tend to invoke qemu_co_queue_next() and
qemu_co_queue_restart_all() occasionally after blocking I/O, so creating
a new BH for each call shouldn't be massively inefficient.

Note that this patch does not add an interface for specifying the
AioContext.  That is left to future patches which will convert CoQueue,
CoMutex, and CoRwlock to expose AioContext.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
2013-03-15 16:07:51 +01:00

193 lines
5.1 KiB
C

/*
* coroutine queues and locks
*
* Copyright (c) 2011 Kevin Wolf <kwolf@redhat.com>
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
#include "qemu-common.h"
#include "block/coroutine.h"
#include "block/coroutine_int.h"
#include "qemu/queue.h"
#include "block/aio.h"
#include "trace.h"
/* Coroutines are awoken from a BH to allow the current coroutine to complete
* its flow of execution. The BH may run after the CoQueue has been destroyed,
* so keep BH data in a separate heap-allocated struct.
*/
typedef struct {
QEMUBH *bh;
QTAILQ_HEAD(, Coroutine) entries;
} CoQueueNextData;
static void qemu_co_queue_next_bh(void *opaque)
{
CoQueueNextData *data = opaque;
Coroutine *next;
trace_qemu_co_queue_next_bh();
while ((next = QTAILQ_FIRST(&data->entries))) {
QTAILQ_REMOVE(&data->entries, next, co_queue_next);
qemu_coroutine_enter(next, NULL);
}
qemu_bh_delete(data->bh);
g_slice_free(CoQueueNextData, data);
}
void qemu_co_queue_init(CoQueue *queue)
{
QTAILQ_INIT(&queue->entries);
/* This will be exposed to callers once there are multiple AioContexts */
queue->ctx = qemu_get_aio_context();
}
void coroutine_fn qemu_co_queue_wait(CoQueue *queue)
{
Coroutine *self = qemu_coroutine_self();
QTAILQ_INSERT_TAIL(&queue->entries, self, co_queue_next);
qemu_coroutine_yield();
assert(qemu_in_coroutine());
}
void coroutine_fn qemu_co_queue_wait_insert_head(CoQueue *queue)
{
Coroutine *self = qemu_coroutine_self();
QTAILQ_INSERT_HEAD(&queue->entries, self, co_queue_next);
qemu_coroutine_yield();
assert(qemu_in_coroutine());
}
static bool qemu_co_queue_do_restart(CoQueue *queue, bool single)
{
Coroutine *next;
CoQueueNextData *data;
if (QTAILQ_EMPTY(&queue->entries)) {
return false;
}
data = g_slice_new(CoQueueNextData);
data->bh = aio_bh_new(queue->ctx, qemu_co_queue_next_bh, data);
QTAILQ_INIT(&data->entries);
qemu_bh_schedule(data->bh);
while ((next = QTAILQ_FIRST(&queue->entries)) != NULL) {
QTAILQ_REMOVE(&queue->entries, next, co_queue_next);
QTAILQ_INSERT_TAIL(&data->entries, next, co_queue_next);
trace_qemu_co_queue_next(next);
if (single) {
break;
}
}
return true;
}
bool qemu_co_queue_next(CoQueue *queue)
{
return qemu_co_queue_do_restart(queue, true);
}
void qemu_co_queue_restart_all(CoQueue *queue)
{
qemu_co_queue_do_restart(queue, false);
}
bool qemu_co_queue_empty(CoQueue *queue)
{
return (QTAILQ_FIRST(&queue->entries) == NULL);
}
void qemu_co_mutex_init(CoMutex *mutex)
{
memset(mutex, 0, sizeof(*mutex));
qemu_co_queue_init(&mutex->queue);
}
void coroutine_fn qemu_co_mutex_lock(CoMutex *mutex)
{
Coroutine *self = qemu_coroutine_self();
trace_qemu_co_mutex_lock_entry(mutex, self);
while (mutex->locked) {
qemu_co_queue_wait(&mutex->queue);
}
mutex->locked = true;
trace_qemu_co_mutex_lock_return(mutex, self);
}
void coroutine_fn qemu_co_mutex_unlock(CoMutex *mutex)
{
Coroutine *self = qemu_coroutine_self();
trace_qemu_co_mutex_unlock_entry(mutex, self);
assert(mutex->locked == true);
assert(qemu_in_coroutine());
mutex->locked = false;
qemu_co_queue_next(&mutex->queue);
trace_qemu_co_mutex_unlock_return(mutex, self);
}
void qemu_co_rwlock_init(CoRwlock *lock)
{
memset(lock, 0, sizeof(*lock));
qemu_co_queue_init(&lock->queue);
}
void qemu_co_rwlock_rdlock(CoRwlock *lock)
{
while (lock->writer) {
qemu_co_queue_wait(&lock->queue);
}
lock->reader++;
}
void qemu_co_rwlock_unlock(CoRwlock *lock)
{
assert(qemu_in_coroutine());
if (lock->writer) {
lock->writer = false;
qemu_co_queue_restart_all(&lock->queue);
} else {
lock->reader--;
assert(lock->reader >= 0);
/* Wakeup only one waiting writer */
if (!lock->reader) {
qemu_co_queue_next(&lock->queue);
}
}
}
void qemu_co_rwlock_wrlock(CoRwlock *lock)
{
while (lock->writer || lock->reader) {
qemu_co_queue_wait(&lock->queue);
}
lock->writer = true;
}