coroutines: Locks

Signed-off-by: Kevin Wolf <kwolf@redhat.com>

Makefile.objs

@@ -12,7 +12,7 @@ oslib-obj-$(CONFIG_POSIX) += oslib-posix.o qemu-thread-posix.o
 
 #######################################################################
 # coroutines
-coroutine-obj-y = qemu-coroutine.o
+coroutine-obj-y = qemu-coroutine.o qemu-coroutine-lock.o
 ifeq ($(CONFIG_UCONTEXT_COROUTINE),y)
 coroutine-obj-$(CONFIG_POSIX) += coroutine-ucontext.o
 else

qemu-coroutine-int.h

@@ -38,6 +38,7 @@ struct Coroutine {
     void *entry_arg;
     Coroutine *caller;
     QLIST_ENTRY(Coroutine) pool_next;
+    QTAILQ_ENTRY(Coroutine) co_queue_next;
 };
 
 Coroutine *qemu_coroutine_new(void);

qemu-coroutine-lock.c

@@ -0,0 +1,124 @@
+/*
+ * 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 "qemu-coroutine.h"
+#include "qemu-coroutine-int.h"
+#include "qemu-queue.h"
+#include "trace.h"
+
+static QTAILQ_HEAD(, Coroutine) unlock_bh_queue =
+    QTAILQ_HEAD_INITIALIZER(unlock_bh_queue);
+
+struct unlock_bh {
+    QEMUBH *bh;
+};
+
+static void qemu_co_queue_next_bh(void *opaque)
+{
+    struct unlock_bh *unlock_bh = opaque;
+    Coroutine *next;
+
+    trace_qemu_co_queue_next_bh();
+    while ((next = QTAILQ_FIRST(&unlock_bh_queue))) {
+        QTAILQ_REMOVE(&unlock_bh_queue, next, co_queue_next);
+        qemu_coroutine_enter(next, NULL);
+    }
+
+    qemu_bh_delete(unlock_bh->bh);
+    qemu_free(unlock_bh);
+}
+
+void qemu_co_queue_init(CoQueue *queue)
+{
+    QTAILQ_INIT(&queue->entries);
+}
+
+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());
+}
+
+bool qemu_co_queue_next(CoQueue *queue)
+{
+    struct unlock_bh *unlock_bh;
+    Coroutine *next;
+
+    next = QTAILQ_FIRST(&queue->entries);
+    if (next) {
+        QTAILQ_REMOVE(&queue->entries, next, co_queue_next);
+        QTAILQ_INSERT_TAIL(&unlock_bh_queue, next, co_queue_next);
+        trace_qemu_co_queue_next(next);
+
+        unlock_bh = qemu_malloc(sizeof(*unlock_bh));
+        unlock_bh->bh = qemu_bh_new(qemu_co_queue_next_bh, unlock_bh);
+        qemu_bh_schedule(unlock_bh->bh);
+    }
+
+    return (next != NULL);
+}
+
+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);
+}

qemu-coroutine.h

@@ -5,6 +5,7 @@
  *
  * Authors:
  *  Stefan Hajnoczi    <stefanha@linux.vnet.ibm.com>
+ *  Kevin Wolf         <kwolf@redhat.com>
  *
  * This work is licensed under the terms of the GNU LGPL, version 2 or later.
  * See the COPYING.LIB file in the top-level directory.
@@ -15,6 +16,7 @@
 #define QEMU_COROUTINE_H
 
 #include <stdbool.h>
+#include "qemu-queue.h"
 
 /**
  * Coroutines are a mechanism for stack switching and can be used for
@@ -92,4 +94,66 @@ Coroutine *coroutine_fn qemu_coroutine_self(void);
  */
 bool qemu_in_coroutine(void);
 
+
+
+/**
+ * CoQueues are a mechanism to queue coroutines in order to continue executing
+ * them later. They provide the fundamental primitives on which coroutine locks
+ * are built.
+ */
+typedef struct CoQueue {
+    QTAILQ_HEAD(, Coroutine) entries;
+} CoQueue;
+
+/**
+ * Initialise a CoQueue. This must be called before any other operation is used
+ * on the CoQueue.
+ */
+void qemu_co_queue_init(CoQueue *queue);
+
+/**
+ * Adds the current coroutine to the CoQueue and transfers control to the
+ * caller of the coroutine.
+ */
+void coroutine_fn qemu_co_queue_wait(CoQueue *queue);
+
+/**
+ * Restarts the next coroutine in the CoQueue and removes it from the queue.
+ *
+ * Returns true if a coroutine was restarted, false if the queue is empty.
+ */
+bool qemu_co_queue_next(CoQueue *queue);
+
+/**
+ * Checks if the CoQueue is empty.
+ */
+bool qemu_co_queue_empty(CoQueue *queue);
+
+
+/**
+ * Provides a mutex that can be used to synchronise coroutines
+ */
+typedef struct CoMutex {
+    bool locked;
+    CoQueue queue;
+} CoMutex;
+
+/**
+ * Initialises a CoMutex. This must be called before any other operation is used
+ * on the CoMutex.
+ */
+void qemu_co_mutex_init(CoMutex *mutex);
+
+/**
+ * Locks the mutex. If the lock cannot be taken immediately, control is
+ * transferred to the caller of the current coroutine.
+ */
+void coroutine_fn qemu_co_mutex_lock(CoMutex *mutex);
+
+/**
+ * Unlocks the mutex and schedules the next coroutine that was waiting for this
+ * lock to be run.
+ */
+void coroutine_fn qemu_co_mutex_unlock(CoMutex *mutex);
+
 #endif /* QEMU_COROUTINE_H */

trace-events

@@ -433,3 +433,11 @@ disable xen_platform_log(char *s) "xen platform: %s"
 disable qemu_coroutine_enter(void *from, void *to, void *opaque) "from %p to %p opaque %p"
 disable qemu_coroutine_yield(void *from, void *to) "from %p to %p"
 disable qemu_coroutine_terminate(void *co) "self %p"
+
+# qemu-coroutine-lock.c
+disable qemu_co_queue_next_bh(void) ""
+disable qemu_co_queue_next(void *next) "next %p"
+disable qemu_co_mutex_lock_entry(void *mutex, void *self) "mutex %p self %p"
+disable qemu_co_mutex_lock_return(void *mutex, void *self) "mutex %p self %p"
+disable qemu_co_mutex_unlock_entry(void *mutex, void *self) "mutex %p self %p"
+disable qemu_co_mutex_unlock_return(void *mutex, void *self) "mutex %p self %p"