// Copyright 2011 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef PPAPI_SHARED_IMPL_CALLBACK_TRACKER_H_
#define PPAPI_SHARED_IMPL_CALLBACK_TRACKER_H_
#include <map>
#include <set>
#include "base/memory/ref_counted.h"
#include "base/synchronization/lock.h"
#include "ppapi/c/pp_resource.h"
#include "ppapi/shared_impl/ppapi_shared_export.h"
namespace ppapi {
class TrackedCallback;
// Pepper callbacks have the following semantics (unless otherwise specified;
// in particular, the below apply to all completion callbacks):
// - Callbacks are always run on the thread where the plugin called a Pepper
// function providing that callback.
// - Callbacks are always called from the message loop of the thread. In
// particular, calling into Pepper will not result in the plugin being
// re-entered via a synchronously-run callback.
// - Each callback will be executed (a.k.a. completed) exactly once.
// - Each callback may be *aborted*, which means that it will be executed with
// result |PP_ERROR_ABORTED| (in the case of completion callbacks). The
// ABORT counts as the callback's one completion.
// - Before |PPP_ShutdownModule()| is called, every pending callback (for every
// instance of that module) will be aborted.
// - Callbacks are usually associated to a resource, whose "deletion" provides
// a "cancellation" (or abort) mechanism -- see below.
// - When a plugin releases its last reference to resource, all callbacks
// associated to that resource are aborted. Even if a non-abortive completion
// of such a callback had previously been scheduled (i.e., posted), that
// callback must now be aborted. The aborts should be scheduled immediately
// (upon the last reference being given up) and should not rely on anything
// else (e.g., a background task to complete or further action from the
// plugin).
// - Abortive completion gives no information about the status of the
// asynchronous operation: The operation may have not yet begun, may be in
// progress, or may be completed (successfully or not). In fact, the
// operation may still proceed after the callback has been aborted.
// - Any output data buffers provided to Pepper are associated with a resource.
// Once that resource is released, no subsequent writes to those buffers
// will occur. When operations occur on background threads, writing to the
// plugin's data buffers should be delayed to happen on the callback's thread
// to ensure that we don't write to the buffers if the callback has been
// aborted (see TrackedCallback::set_completion_task()).
//
// Thread-safety notes:
// |CallbackTracker| uses a lock to protect its dictionary of callbacks. This
// is primarily to allow the safe removal of callbacks from any thread without
// requiring that the |ProxyLock| is held. Methods that may invoke a callback
// need to have the |ProxyLock| (and those methods assert that it's acquired).
// |TrackedCallback| is thread-safe ref-counted, so objects which live on
// different threads may keep references. Releasing a reference to
// |TrackedCallback| on a different thread (possibly causing destruction) is
// also okay.
//
// |CallbackTracker| tracks pending Pepper callbacks for a single instance. It
// also tracks, for each resource ID, which callbacks are pending. Just before
// a callback is completed, it is removed from the tracker. We use
// |CallbackTracker| for two things: (1) to ensure that all callbacks are
// properly aborted before instance shutdown, and (2) to ensure that all
// callbacks associated with a given resource are aborted when a plugin instance
// releases its last reference to that resource.
class PPAPI_SHARED_EXPORT CallbackTracker
: public base::RefCountedThreadSafe<CallbackTracker> {
public:
CallbackTracker();
CallbackTracker(const CallbackTracker&) = delete;
CallbackTracker& operator=(const CallbackTracker&) = delete;
// Abort all callbacks (synchronously).
void AbortAll();
// Abort all callbacks associated to the given resource ID (which must be
// valid, i.e., nonzero) by posting a task (or tasks).
void PostAbortForResource(PP_Resource resource_id);
private:
friend class base::RefCountedThreadSafe<CallbackTracker>;
~CallbackTracker();
// |TrackedCallback| are expected to automatically add and
// remove themselves from their provided |CallbackTracker|.
friend class TrackedCallback;
void Add(const scoped_refptr<TrackedCallback>& tracked_callback);
void Remove(const scoped_refptr<TrackedCallback>& tracked_callback);
// For each resource ID with a pending callback, store a set with its pending
// callbacks. (Resource ID 0 is used for callbacks not associated to a valid
// resource.) If a resource ID is re-used for another resource, there may be
// aborted callbacks corresponding to the original resource in that set; these
// will be removed when they are completed (abortively).
typedef std::set<scoped_refptr<TrackedCallback> > CallbackSet;
typedef std::map<PP_Resource, CallbackSet> CallbackSetMap;
CallbackSetMap pending_callbacks_;
// Used to ensure we don't add any callbacks after AbortAll.
bool abort_all_called_;
base::Lock lock_;
};
} // namespace ppapi
#endif // PPAPI_SHARED_IMPL_CALLBACK_TRACKER_H_
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