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02ffb50448
qemu_co_queue_next(&queue) arranges that the next queued coroutine is run at a later point in time. This deferred restart is useful because the caller may not want to transfer control yet. This behavior was implemented using QEMUBH in the past, which meant that CoQueue (and hence CoMutex and CoRwlock) had a dependency on the AioContext event loop. This hidden dependency causes trouble when we move to a world with multiple event loops - now qemu_co_queue_next() needs to know which event loop to schedule the QEMUBH in. After pondering how to stash AioContext I realized the best solution is to not use AioContext at all. This patch implements the deferred restart behavior purely in terms of coroutines and no longer uses QEMUBH. Here is how it works: Each Coroutine has a wakeup queue that starts out empty. When qemu_co_queue_next() is called, the next coroutine is added to our wakeup queue. The wakeup queue is processed when we yield or terminate. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
136 lines
2.9 KiB
C
136 lines
2.9 KiB
C
/*
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* QEMU coroutines
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*
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* Copyright IBM, Corp. 2011
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*
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* Authors:
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* Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
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* Kevin Wolf <kwolf@redhat.com>
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*
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* This work is licensed under the terms of the GNU LGPL, version 2 or later.
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* See the COPYING.LIB file in the top-level directory.
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*
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*/
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#include "trace.h"
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#include "qemu-common.h"
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#include "qemu/thread.h"
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#include "block/coroutine.h"
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#include "block/coroutine_int.h"
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enum {
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/* Maximum free pool size prevents holding too many freed coroutines */
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POOL_MAX_SIZE = 64,
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};
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/** Free list to speed up creation */
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static QemuMutex pool_lock;
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static QSLIST_HEAD(, Coroutine) pool = QSLIST_HEAD_INITIALIZER(pool);
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static unsigned int pool_size;
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Coroutine *qemu_coroutine_create(CoroutineEntry *entry)
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{
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Coroutine *co;
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qemu_mutex_lock(&pool_lock);
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co = QSLIST_FIRST(&pool);
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if (co) {
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QSLIST_REMOVE_HEAD(&pool, pool_next);
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pool_size--;
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}
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qemu_mutex_unlock(&pool_lock);
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if (!co) {
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co = qemu_coroutine_new();
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}
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co->entry = entry;
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QTAILQ_INIT(&co->co_queue_wakeup);
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return co;
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}
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static void coroutine_delete(Coroutine *co)
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{
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qemu_mutex_lock(&pool_lock);
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if (pool_size < POOL_MAX_SIZE) {
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QSLIST_INSERT_HEAD(&pool, co, pool_next);
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co->caller = NULL;
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pool_size++;
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qemu_mutex_unlock(&pool_lock);
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return;
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}
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qemu_mutex_unlock(&pool_lock);
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qemu_coroutine_delete(co);
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}
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static void __attribute__((constructor)) coroutine_pool_init(void)
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{
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qemu_mutex_init(&pool_lock);
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}
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static void __attribute__((destructor)) coroutine_pool_cleanup(void)
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{
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Coroutine *co;
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Coroutine *tmp;
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QSLIST_FOREACH_SAFE(co, &pool, pool_next, tmp) {
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QSLIST_REMOVE_HEAD(&pool, pool_next);
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qemu_coroutine_delete(co);
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}
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qemu_mutex_destroy(&pool_lock);
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}
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static void coroutine_swap(Coroutine *from, Coroutine *to)
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{
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CoroutineAction ret;
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ret = qemu_coroutine_switch(from, to, COROUTINE_YIELD);
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qemu_co_queue_run_restart(to);
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switch (ret) {
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case COROUTINE_YIELD:
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return;
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case COROUTINE_TERMINATE:
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trace_qemu_coroutine_terminate(to);
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coroutine_delete(to);
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return;
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default:
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abort();
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}
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}
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void qemu_coroutine_enter(Coroutine *co, void *opaque)
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{
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Coroutine *self = qemu_coroutine_self();
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trace_qemu_coroutine_enter(self, co, opaque);
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if (co->caller) {
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fprintf(stderr, "Co-routine re-entered recursively\n");
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abort();
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}
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co->caller = self;
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co->entry_arg = opaque;
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coroutine_swap(self, co);
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}
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void coroutine_fn qemu_coroutine_yield(void)
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{
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Coroutine *self = qemu_coroutine_self();
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Coroutine *to = self->caller;
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trace_qemu_coroutine_yield(self, to);
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if (!to) {
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fprintf(stderr, "Co-routine is yielding to no one\n");
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abort();
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}
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self->caller = NULL;
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coroutine_swap(self, to);
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}
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