@@ -232,7 +232,8 @@ QIOTask *qio_task_new(Object *source,
*
* Run a task in a background thread. When @worker
* returns it will call qio_task_complete() in
- * the event thread context that provided.
+ * the thread that is running the main loop associated
+ * with @context.
*/
void qio_task_run_in_thread(QIOTask *task,
QIOTaskWorker worker,
@@ -240,6 +241,32 @@ void qio_task_run_in_thread(QIOTask *task,
GDestroyNotify destroy,
GMainContext *context);
+
+/**
+ * qio_task_wait_thread:
+ * @task: the task struct
+ *
+ * Wait for completion of a task that was previously
+ * invoked using qio_task_run_in_thread. This MUST
+ * ONLY be invoked if the task has not already
+ * completed, since after the completion callback
+ * is invoked, @task will have been freed.
+ *
+ * To avoid racing with execution of the completion
+ * callback provided with qio_task_new, this method
+ * MUST ONLY be invoked from the thread that is
+ * running the main loop associated with @context
+ * parameter to qio_task_run_in_thread.
+ *
+ * When the thread has completed, the completion
+ * callback provided to qio_task_new will be invoked.
+ * When that callback returns @task will be freed,
+ * so @task must not be referenced after this
+ * method completes.
+ */
+void qio_task_wait_thread(QIOTask *task);
+
+
/**
* qio_task_complete:
* @task: the task struct
@@ -29,6 +29,7 @@ struct QIOTaskThreadData {
gpointer opaque;
GDestroyNotify destroy;
GMainContext *context;
+ GSource *completion;
};
@@ -40,6 +41,8 @@ struct QIOTask {
Error *err;
gpointer result;
GDestroyNotify destroyResult;
+ QemuMutex thread_lock;
+ QemuCond thread_cond;
struct QIOTaskThreadData *thread;
};
@@ -58,6 +61,8 @@ QIOTask *qio_task_new(Object *source,
task->func = func;
task->opaque = opaque;
task->destroy = destroy;
+ qemu_mutex_init(&task->thread_lock);
+ qemu_cond_init(&task->thread_cond);
trace_qio_task_new(task, source, func, opaque);
@@ -77,6 +82,9 @@ static void qio_task_free(QIOTask *task)
}
object_unref(task->source);
+ qemu_mutex_destroy(&task->thread_lock);
+ qemu_cond_destroy(&task->thread_cond);
+
g_free(task);
}
@@ -86,7 +94,6 @@ static gboolean qio_task_thread_result(gpointer opaque)
QIOTask *task = opaque;
trace_qio_task_thread_result(task);
- qio_task_complete(task);
if (task->thread->destroy) {
task->thread->destroy(task->thread->opaque);
@@ -98,6 +105,7 @@ static gboolean qio_task_thread_result(gpointer opaque)
g_free(task->thread);
task->thread = NULL;
+ qio_task_complete(task);
return FALSE;
}
@@ -106,7 +114,6 @@ static gboolean qio_task_thread_result(gpointer opaque)
static gpointer qio_task_thread_worker(gpointer opaque)
{
QIOTask *task = opaque;
- GSource *idle;
trace_qio_task_thread_run(task);
@@ -119,9 +126,17 @@ static gpointer qio_task_thread_worker(gpointer opaque)
*/
trace_qio_task_thread_exit(task);
- idle = g_idle_source_new();
- g_source_set_callback(idle, qio_task_thread_result, task, NULL);
- g_source_attach(idle, task->thread->context);
+ qemu_mutex_lock(&task->thread_lock);
+
+ task->thread->completion = g_idle_source_new();
+ g_source_set_callback(task->thread->completion,
+ qio_task_thread_result, task, NULL);
+ g_source_attach(task->thread->completion,
+ task->thread->context);
+ trace_qio_task_thread_source_attach(task, task->thread->completion);
+
+ qemu_cond_signal(&task->thread_cond);
+ qemu_mutex_unlock(&task->thread_lock);
return NULL;
}
@@ -156,6 +171,22 @@ void qio_task_run_in_thread(QIOTask *task,
}
+void qio_task_wait_thread(QIOTask *task)
+{
+ qemu_mutex_lock(&task->thread_lock);
+ g_assert(task->thread != NULL);
+ while (task->thread->completion == NULL) {
+ qemu_cond_wait(&task->thread_cond, &task->thread_lock);
+ }
+
+ trace_qio_task_thread_source_cancel(task, task->thread->completion);
+ g_source_destroy(task->thread->completion);
+ qemu_mutex_unlock(&task->thread_lock);
+
+ qio_task_thread_result(task);
+}
+
+
void qio_task_complete(QIOTask *task)
{
task->func(task, task->opaque);
@@ -7,6 +7,8 @@ qio_task_thread_start(void *task, void *worker, void *opaque) "Task thread start
qio_task_thread_run(void *task) "Task thread run task=%p"
qio_task_thread_exit(void *task) "Task thread exit task=%p"
qio_task_thread_result(void *task) "Task thread result task=%p"
+qio_task_thread_source_attach(void *task, void *source) "Task thread source attach task=%p source=%p"
+qio_task_thread_source_cancel(void *task, void *source) "Task thread source cancel task=%p source=%p"
# io/channel-socket.c
qio_channel_socket_new(void *ioc) "Socket new ioc=%p"
Add the ability for a caller to wait for completion of the background thread to synchronously dispatch its result, without needing to wait for the main loop to run the idle callback. This method needs very careful usage to avoid a dangerous race condition with the free'ing of the task. The completion callback is normally invoked from an idle callback registered with the main loop context. The qio_task_wait_thread method must only be called if the completion callback has not yet run. The only safe way to achieve this is to run the qio_task_wait_thread method from the thread that executes the main loop. It is generally a bad idea to use this method since it will block execution of the main loop, however, the design of the character devices and its usage from vhostuser already requires blocking execution. Signed-off-by: Daniel P. Berrangé <berrange@redhat.com> --- include/io/task.h | 29 ++++++++++++++++++++++++++++- io/task.c | 41 ++++++++++++++++++++++++++++++++++++----- io/trace-events | 2 ++ 3 files changed, 66 insertions(+), 6 deletions(-)