Centralized thread cancellation in processor_t

This ensures that no threads are active when plugins and the rest of the
daemon are unloaded.

callback_job_t was simplified a lot in the process as its main
functionality is now contained in processor_t.  The parent-child
relationships were abandoned as these were only needed to simplify job
cancellation.

src/libstrongswan/processing/jobs/callback_job.c

@@ -51,42 +51,9 @@ struct private_callback_job_t {
 	callback_job_cleanup_t cleanup;
 
 	/**
-	 * thread of the job, if running
+	 * cancel function
 	 */
-	thread_t *thread;
-
-	/**
-	 * mutex to access private job data
-	 */
-	mutex_t *mutex;
-
-	/**
-	 * list of associated child jobs
-	 */
-	linked_list_t *children;
-
-	/**
-	 * parent of this job, or NULL
-	 */
-	private_callback_job_t *parent;
-
-	/**
-	 * TRUE if the job got canceled
-	 */
-	bool canceled;
-
-	/**
-	 * condvar to synchronize the cancellation/destruction of the job
-	 */
-	condvar_t *destroyable;
-
-	/**
-	 * semaphore to synchronize the termination of the assigned thread.
-	 *
-	 * separately created during cancellation, so that we can wait on it
-	 * without risking that it gets destroyed too early during destruction.
-	 */
-	semaphore_t *terminated;
+	callback_job_cancel_t cancel;
 
 	/**
 	 * Priority of this job
@@ -94,131 +61,26 @@ struct private_callback_job_t {
 	job_priority_t prio;
 };
 
-/**
- * unregister a child from its parent, if any.
- * note: this->mutex has to be locked
- */
-static void unregister(private_callback_job_t *this)
-{
-	if (this->parent)
-	{
-		this->parent->mutex->lock(this->parent->mutex);
-		if (this->parent->canceled && !this->canceled)
-		{
-			/* if the parent has been canceled but we have not yet, we do not
-			 * unregister until we got canceled by the parent. */
-			this->parent->mutex->unlock(this->parent->mutex);
-			this->destroyable->wait(this->destroyable, this->mutex);
-			this->parent->mutex->lock(this->parent->mutex);
-		}
-		this->parent->children->remove(this->parent->children, this, NULL);
-		this->parent->mutex->unlock(this->parent->mutex);
-		this->parent = NULL;
-	}
-}
-
 METHOD(job_t, destroy, void,
 	private_callback_job_t *this)
 {
-	this->mutex->lock(this->mutex);
-	unregister(this);
 	if (this->cleanup)
 	{
 		this->cleanup(this->data);
 	}
-	if (this->terminated)
-	{
-		this->terminated->post(this->terminated);
-	}
-	this->children->destroy(this->children);
-	this->destroyable->destroy(this->destroyable);
-	this->mutex->unlock(this->mutex);
-	this->mutex->destroy(this->mutex);
 	free(this);
 }
 
-METHOD(callback_job_t, cancel, void,
-	private_callback_job_t *this)
-{
-	callback_job_t *child;
-	semaphore_t *terminated = NULL;
-
-	this->mutex->lock(this->mutex);
-	this->canceled = TRUE;
-	/* terminate children */
-	while (this->children->get_first(this->children, (void**)&child) == SUCCESS)
-	{
-		this->mutex->unlock(this->mutex);
-		child->cancel(child);
-		this->mutex->lock(this->mutex);
-	}
-	if (this->thread)
-	{
-		/* terminate the thread, if there is currently one executing the job.
-		 * we wait for its termination using a semaphore */
-		this->thread->cancel(this->thread);
-		terminated = this->terminated = semaphore_create(0);
-	}
-	else
-	{
-		/* if the job is currently queued, it gets terminated later.
-		 * we can't wait, because it might not get executed at all.
-		 * we also unregister the queued job manually from its parent (the
-		 * others get unregistered during destruction) */
-		unregister(this);
-	}
-	this->destroyable->signal(this->destroyable);
-	this->mutex->unlock(this->mutex);
-
-	if (terminated)
-	{
-		terminated->wait(terminated);
-		terminated->destroy(terminated);
-	}
-}
-
 METHOD(job_t, execute, job_requeue_t,
 	private_callback_job_t *this)
 {
-	bool requeue = FALSE;
+	return this->callback(this->data);
+}
 
-	this->mutex->lock(this->mutex);
-	this->thread = thread_current();
-	this->mutex->unlock(this->mutex);
-
-	while (TRUE)
-	{
-		this->mutex->lock(this->mutex);
-		if (this->canceled)
-		{
-			this->mutex->unlock(this->mutex);
-			break;
-		}
-		this->mutex->unlock(this->mutex);
-		switch (this->callback(this->data))
-		{
-			case JOB_REQUEUE_DIRECT:
-				continue;
-			case JOB_REQUEUE_FAIR:
-			{
-				requeue = TRUE;
-				break;
-			}
-			case JOB_REQUEUE_NONE:
-			default:
-			{
-				break;
-			}
-		}
-		break;
-	}
-	this->mutex->lock(this->mutex);
-	this->thread = NULL;
-	this->mutex->unlock(this->mutex);
-	/* manually create a cancellation point to avoid that a canceled thread
-	 * goes back into the thread pool at all */
-	thread_cancellation_point();
-	return requeue ? JOB_REQUEUE_FAIR : JOB_REQUEUE_NONE;
+METHOD(job_t, cancel, bool,
+	private_callback_job_t *this)
+{
+	return this->cancel(this->data);
 }
 
 METHOD(job_t, get_priority, job_priority_t,
@@ -231,8 +93,8 @@ METHOD(job_t, get_priority, job_priority_t,
  * Described in header.
  */
 callback_job_t *callback_job_create_with_prio(callback_job_cb_t cb, void *data,
-					callback_job_cleanup_t cleanup, callback_job_t *parent,
-					job_priority_t prio)
+				callback_job_cleanup_t cleanup, callback_job_cancel_t cancel,
+				job_priority_t prio)
 {
 	private_callback_job_t *this;
 
@@ -243,24 +105,17 @@ callback_job_t *callback_job_create_with_prio(callback_job_cb_t cb, void *data,
 				.get_priority = _get_priority,
 				.destroy = _destroy,
 			},
-			.cancel = _cancel,
 		},
-		.mutex = mutex_create(MUTEX_TYPE_DEFAULT),
 		.callback = cb,
 		.data = data,
 		.cleanup = cleanup,
-		.children = linked_list_create(),
-		.parent = (private_callback_job_t*)parent,
-		.destroyable = condvar_create(CONDVAR_TYPE_DEFAULT),
+		.cancel = cancel,
 		.prio = prio,
 	);
 
-	/* register us at parent */
-	if (parent)
+	if (cancel)
 	{
-		this->parent->mutex->lock(this->parent->mutex);
-		this->parent->children->insert_last(this->parent->children, this);
-		this->parent->mutex->unlock(this->parent->mutex);
+		this->public.job.cancel = _cancel;
 	}
 
 	return &this->public;
@@ -271,8 +126,8 @@ callback_job_t *callback_job_create_with_prio(callback_job_cb_t cb, void *data,
  */
 callback_job_t *callback_job_create(callback_job_cb_t cb, void *data,
 									callback_job_cleanup_t cleanup,
-									callback_job_t *parent)
+									callback_job_cancel_t cancel)
 {
-	return callback_job_create_with_prio(cb, data, cleanup, parent,
+	return callback_job_create_with_prio(cb, data, cleanup, cancel,
 										 JOB_PRIO_MEDIUM);
 }

src/libstrongswan/processing/jobs/callback_job.h

@@ -1,4 +1,5 @@
 /*
+ * Copyright (C) 2012 Tobias Brunner
  * Copyright (C) 2007-2011 Martin Willi
  * Copyright (C) 2011 revosec AG
  * Hochschule fuer Technik Rapperswil
@@ -46,10 +47,21 @@ typedef job_requeue_t (*callback_job_cb_t)(void *data);
  * to supply to the constructor.
  *
  * @param data			param supplied to job
- * @return				requeing policy how to requeue the job
  */
 typedef void (*callback_job_cleanup_t)(void *data);
 
+/**
+ * Cancellation function to use for the callback job.
+ *
+ * Optional function to be called when a job has to be canceled.
+ *
+ * See job_t.cancel() for details on the return value.
+ *
+ * @param data			param supplied to job
+ * @return				TRUE if canceled, FALSE to explicitly cancel the thread
+ */
+typedef bool (*callback_job_cancel_t)(void *data);
+
 /**
  * Class representing an callback Job.
  *
@@ -64,14 +76,6 @@ struct callback_job_t {
 	 */
 	job_t job;
 
-	/**
-	 * Cancel the job's thread and wait for its termination.
-	 *
-	 * This only works reliably for jobs that always use JOB_REQUEUE_FAIR or
-	 * JOB_REQUEUE_DIRECT, otherwise the job may already be destroyed when
-	 * cancel is called.
-	 */
-	void (*cancel)(callback_job_t *this);
 };
 
 /**
@@ -79,19 +83,20 @@ struct callback_job_t {
  *
  * The cleanup function is called when the job gets destroyed to destroy
  * the associated data.
- * If parent is not NULL, the specified job gets an association. Whenever
- * the parent gets cancelled (or runs out), all of its children are cancelled,
- * too.
+ *
+ * The cancel function is optional and should only be provided if the callback
+ * function calls potentially blocking functions and/or always returns
+ * JOB_REQUEUE_DIRECT.
  *
  * @param cb				callback to call from the processor
  * @param data				user data to supply to callback
  * @param cleanup			destructor for data on destruction, or NULL
- * @param parent			parent of this job
+ * @param cancel			function to cancel the job, or NULL
  * @return					callback_job_t object
  */
 callback_job_t *callback_job_create(callback_job_cb_t cb, void *data,
 									callback_job_cleanup_t cleanup,
-									callback_job_t *parent);
+									callback_job_cancel_t cancel);
 
 /**
  * Creates a callback job, with priority.
@@ -101,12 +106,12 @@ callback_job_t *callback_job_create(callback_job_cb_t cb, void *data,
  * @param cb				callback to call from the processor
  * @param data				user data to supply to callback
  * @param cleanup			destructor for data on destruction, or NULL
- * @param parent			parent of this job
+ * @param cancel			function to cancel the job, or NULL
  * @param prio				job priority
  * @return					callback_job_t object
  */
 callback_job_t *callback_job_create_with_prio(callback_job_cb_t cb, void *data,
-					callback_job_cleanup_t cleanup, callback_job_t *parent,
-					job_priority_t prio);
+				callback_job_cleanup_t cleanup, callback_job_cancel_t cancel,
+				job_priority_t prio);
 
 #endif /** CALLBACK_JOB_H_ @}*/

src/libstrongswan/processing/jobs/job.h

@@ -102,6 +102,26 @@ struct job_t {
 	 */
 	job_requeue_t (*execute) (job_t *this);
 
+	/**
+	 * Cancel a job.
+	 *
+	 * Implementing this method is optional.  It allows potentially blocking
+	 * jobs to be canceled during shutdown.
+	 *
+	 * If no special action is to be taken simply return FALSE then the thread
+	 * executing the job will be canceled.  If TRUE is returned the job is
+	 * expected to return from execute() itself (i.e. the thread won't be
+	 * canceled explicitly and can still be joined later).
+	 * Jobs that return FALSE have to make sure they provide the appropriate
+	 * cancellation points.
+	 *
+	 * @note Regular jobs that do not block MUST NOT implement this method.
+	 * @note This method could be called even before execute() has been called.
+	 *
+	 * @return			FALSE to cancel the thread, TRUE if canceled otherwise
+	 */
+	bool (*cancel)(job_t *this);
+
 	/**
 	 * Get the priority of a job.
 	 *
@@ -117,7 +137,7 @@ struct job_t {
 	 *
 	 * Use the status of a job to decide what to do during destruction.
 	 */
-	void (*destroy) (job_t *this);
+	void (*destroy)(job_t *this);
 };
 
 #endif /** JOB_H_ @}*/

src/libstrongswan/processing/processor.c

@@ -88,7 +88,6 @@ struct private_processor_t {
 	condvar_t *thread_terminated;
 };
 
-
 /**
  * Worker thread
  */
@@ -222,26 +221,38 @@ static void process_jobs(worker_thread_t *worker)
 					{
 						break;
 					}
+					else if (!worker->job->cancel)
+					{	/* only allow cancelable jobs to requeue directly */
+						requeue = JOB_REQUEUE_FAIR;
+						break;
+					}
 				}
 				thread_cleanup_pop(FALSE);
 				this->mutex->lock(this->mutex);
 				this->working_threads[i]--;
-				switch (requeue)
+				if (worker->job->status == JOB_STATUS_CANCELED)
+				{	/* job was canceled via a custom cancel() method or did not
+					 * use JOB_REQUEUE_TYPE_DIRECT */
+					worker->job->destroy(worker->job);
+				}
+				else
 				{
-					case JOB_REQUEUE_NONE:
-						worker->job->status = JOB_STATUS_DONE;
-						worker->job->destroy(worker->job);
-						break;
-					case JOB_REQUEUE_FAIR:
-						worker->job->status = JOB_STATUS_QUEUED;
-						this->jobs[i]->insert_last(this->jobs[i], worker->job);
-						this->job_added->signal(this->job_added);
-						break;
-					case JOB_REQUEUE_SCHEDULED:
-						worker->job->status = JOB_STATUS_QUEUED;
-						/* fall-through */
-					default:
-						break;
+					switch (requeue)
+					{
+						case JOB_REQUEUE_NONE:
+							worker->job->status = JOB_STATUS_DONE;
+							worker->job->destroy(worker->job);
+							break;
+						case JOB_REQUEUE_FAIR:
+							worker->job->status = JOB_STATUS_QUEUED;
+							this->jobs[i]->insert_last(this->jobs[i],
+													   worker->job);
+							this->job_added->signal(this->job_added);
+							break;
+						case JOB_REQUEUE_SCHEDULED:
+						default:
+							break;
+					}
 				}
 				break;
 			}
@@ -364,14 +375,29 @@ METHOD(processor_t, set_threads, void,
 	this->mutex->unlock(this->mutex);
 }
 
-METHOD(processor_t, destroy, void,
+METHOD(processor_t, cancel, void,
 	private_processor_t *this)
 {
+	enumerator_t *enumerator;
 	worker_thread_t *worker;
-	int i;
 
-	set_threads(this, 0);
 	this->mutex->lock(this->mutex);
+	this->desired_threads = 0;
+	/* cancel potentially blocking jobs */
+	enumerator = this->threads->create_enumerator(this->threads);
+	while (enumerator->enumerate(enumerator, (void**)&worker))
+	{
+		if (worker->job && worker->job->cancel)
+		{
+			worker->job->status = JOB_STATUS_CANCELED;
+			if (!worker->job->cancel(worker->job))
+			{	/* job requests to be canceled explicitly, otherwise we assume
+				 * the thread terminates itself and can be joined */
+				worker->thread->cancel(worker->thread);
+			}
+		}
+	}
+	enumerator->destroy(enumerator);
 	while (this->total_threads > 0)
 	{
 		this->job_added->broadcast(this->job_added);
@@ -384,6 +410,14 @@ METHOD(processor_t, destroy, void,
 		free(worker);
 	}
 	this->mutex->unlock(this->mutex);
+}
+
+METHOD(processor_t, destroy, void,
+	private_processor_t *this)
+{
+	int i;
+
+	cancel(this);
 	this->thread_terminated->destroy(this->thread_terminated);
 	this->job_added->destroy(this->job_added);
 	this->mutex->destroy(this->mutex);
@@ -411,6 +445,7 @@ processor_t *processor_create()
 			.get_job_load = _get_job_load,
 			.queue_job = _queue_job,
 			.set_threads = _set_threads,
+			.cancel = _cancel,
 			.destroy = _destroy,
 		},
 		.threads = linked_list_create(),

src/libstrongswan/processing/processor.h

@@ -1,4 +1,5 @@
 /*
+ * Copyright (C) 2012 Tobias Brunner
  * Copyright (C) 2005-2007 Martin Willi
  * Copyright (C) 2005 Jan Hutter
  * Hochschule fuer Technik Rapperswil
@@ -78,13 +79,20 @@ struct processor_t {
 	 *
 	 * If the number of threads is smaller than number of currently running
 	 * threads, thread count is decreased. Use 0 to disable the processor.
-	 * This call blocks if it decreases thread count until threads have
-	 * terminated, so make sure there are not too many blocking jobs.
+	 *
+	 * This call does not block and wait for threads to terminate if the number
+	 * of threads is reduced.  Instead use cancel() for that during shutdown.
 	 *
 	 * @param count			number of threads to allocate
 	 */
 	void (*set_threads)(processor_t *this, u_int count);
 
+	/**
+	 * Sets the number of threads to 0 and cancels all blocking jobs, then waits
+	 * for all threads to be terminated.
+	 */
+	void (*cancel)(processor_t *this);
+
 	/**
 	 * Destroy a processor object.
 	 */

src/libstrongswan/processing/scheduler.c

@@ -67,11 +67,6 @@ struct private_scheduler_t {
 	 */
 	 scheduler_t public;
 
-	/**
-	 * Job which queues scheduled jobs to the processor.
-	 */
-	callback_job_t *job;
-
 	/**
 	 * The heap in which the events are stored.
 	 */
@@ -309,7 +304,6 @@ METHOD(scheduler_t, destroy, void,
 	private_scheduler_t *this)
 {
 	event_t *event;
-	this->job->cancel(this->job);
 	this->condvar->destroy(this->condvar);
 	this->mutex->destroy(this->mutex);
 	while ((event = remove_event(this)) != NULL)
@@ -326,6 +320,7 @@ METHOD(scheduler_t, destroy, void,
 scheduler_t * scheduler_create()
 {
 	private_scheduler_t *this;
+	callback_job_t *job;
 
 	INIT(this,
 		.public = {
@@ -342,9 +337,9 @@ scheduler_t * scheduler_create()
 
 	this->heap = (event_t**)calloc(this->heap_size + 1, sizeof(event_t*));
 
-	this->job = callback_job_create_with_prio((callback_job_cb_t)schedule,
-										this, NULL, NULL, JOB_PRIO_CRITICAL);
-	lib->processor->queue_job(lib->processor, (job_t*)this->job);
+	job = callback_job_create_with_prio((callback_job_cb_t)schedule, this,
+										NULL, return_false, JOB_PRIO_CRITICAL);
+	lib->processor->queue_job(lib->processor, (job_t*)job);
 
 	return &this->public;
 }