ppapi/shared_impl/callback_tracker.h

   1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef PPAPI_SHARED_IMPL_CALLBACK_TRACKER_H_
   6 #define PPAPI_SHARED_IMPL_CALLBACK_TRACKER_H_
   7
   8 #include <map>
   9 #include <set>
  10
  11 #include "base/basictypes.h"
  12 #include "base/memory/ref_counted.h"
  13 #include "ppapi/c/pp_resource.h"
  14 #include "ppapi/shared_impl/ppapi_shared_export.h"
  15
  16 namespace ppapi {
  17
  18 class TrackedCallback;
  19
  20 // Pepper callbacks have the following semantics (unless otherwise specified;
  21 // in particular, the below apply to all completion callbacks):
  22 //  - Callbacks are always run on the main thread.
  23 //  - Callbacks are always called from the main message loop. In particular,
  24 //    calling into Pepper will not result in the plugin being re-entered via a
  25 //    synchronously-run callback.
  26 //  - Each callback will be executed (a.k.a. completed) exactly once.
  27 //  - Each callback may be *aborted*, which means that it will be executed with
  28 //    result |PP_ERROR_ABORTED| (in the case of completion callbacks).
  29 //  - Before |PPP_ShutdownModule()| is called, every pending callback (for that
  30 //    module) will be aborted.
  31 //  - Callbacks are usually associated to a resource, whose "deletion" provides
  32 //    a "cancellation" (or abort) mechanism -- see below.
  33 //  - When a plugin releases its last reference to resource, all callbacks
  34 //    associated to that resource are aborted. Even if a non-abortive completion
  35 //    of such a callback had previously been scheduled (i.e., posted), that
  36 //    callback must now be aborted. The aborts should be scheduled immediately
  37 //    (upon the last reference being given up) and should not rely on anything
  38 //    else (e.g., a background task to complete or further action from the
  39 //    plugin).
  40 //  - Abortive completion gives no information about the status of the
  41 //    asynchronous operation: The operation may have not yet begun, may be in
  42 //    progress, or may be completed (successfully or not). In fact, the
  43 //    operation may still proceed after the callback has been aborted.
  44 //  - Any output data buffers provided to Pepper are associated with a resource.
  45 //    Once that resource is released, no subsequent writes to those buffers. (If
  46 //    background threads are set up to write into such buffers, the final
  47 //    release operation should not return into the plugin until it can
  48 //    guaranteed that those threads will no longer write into the buffers.)
  49 //
  50 // Thread-safety notes:
  51 // Currently, everything should happen on the main thread. The objects are
  52 // thread-safe ref-counted, so objects which live on different threads may keep
  53 // references. Releasing a reference to |TrackedCallback| on a different thread
  54 // (possibly causing destruction) is also okay. Otherwise, all methods should be
  55 // called only from the main thread.
  56
  57 // |CallbackTracker| tracks pending Pepper callbacks for a single module. It
  58 // also tracks, for each resource ID, which callbacks are pending. When a
  59 // callback is (just about to be) completed, it is removed from the tracker. We
  60 // use |CallbackTracker| for two things: (1) to ensure that all callbacks are
  61 // properly aborted before module shutdown, and (2) to ensure that all callbacks
  62 // associated to a given resource are aborted when a plugin (module) releases
  63 // its last reference to that resource.
  64 class PPAPI_SHARED_EXPORT CallbackTracker
  65     : public base::RefCountedThreadSafe<CallbackTracker> {
  66  public:
  67   CallbackTracker();
  68
  69   // Abort all callbacks (synchronously).
  70   void AbortAll();
  71
  72   // Abort all callbacks associated to the given resource ID (which must be
  73   // valid, i.e., nonzero) by posting a task (or tasks).
  74   void PostAbortForResource(PP_Resource resource_id);
  75
  76  private:
  77   friend class base::RefCountedThreadSafe<CallbackTracker>;
  78   ~CallbackTracker();
  79
  80   // |TrackedCallback| are expected to automatically add and
  81   // remove themselves from their provided |CallbackTracker|.
  82   friend class TrackedCallback;
  83   void Add(const scoped_refptr<TrackedCallback>& tracked_callback);
  84   void Remove(const scoped_refptr<TrackedCallback>& tracked_callback);
  85
  86   // For each resource ID with a pending callback, store a set with its pending
  87   // callbacks. (Resource ID 0 is used for callbacks not associated to a valid
  88   // resource.) If a resource ID is re-used for another resource, there may be
  89   // aborted callbacks corresponding to the original resource in that set; these
  90   // will be removed when they are completed (abortively).
  91   typedef std::set<scoped_refptr<TrackedCallback> > CallbackSet;
  92   typedef std::map<PP_Resource, CallbackSet> CallbackSetMap;
  93   CallbackSetMap pending_callbacks_;
  94
  95   DISALLOW_COPY_AND_ASSIGN(CallbackTracker);
  96 };
  97
  98 }  // namespace ppapi
  99
 100 #endif  // PPAPI_SHARED_IMPL_CALLBACK_TRACKER_H_