ppapi/shared_impl/tracked_callback.h

   1 // Copyright (c) 2012 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_TRACKED_CALLBACK_H_
   6 #define PPAPI_SHARED_IMPL_TRACKED_CALLBACK_H_
   7
   8 #include <map>
   9 #include <set>
  10
  11 #include "base/basictypes.h"
  12 #include "base/callback.h"
  13 #include "base/memory/ref_counted.h"
  14 #include "base/memory/scoped_ptr.h"
  15 #include "base/synchronization/condition_variable.h"
  16 #include "ppapi/c/pp_completion_callback.h"
  17 #include "ppapi/c/pp_instance.h"
  18 #include "ppapi/c/pp_resource.h"
  19 #include "ppapi/shared_impl/ppapi_shared_export.h"
  20 #include "ppapi/shared_impl/ppb_message_loop_shared.h"
  21
  22 namespace ppapi {
  23
  24 class CallbackTracker;
  25 class MessageLoopShared;
  26 class Resource;
  27
  28 namespace thunk {
  29 namespace subtle {
  30 // For a friend declaration below.
  31 class EnterBase;
  32 }
  33 }
  34
  35 // |TrackedCallback| represents a tracked Pepper callback (from the browser to
  36 // the plugin), typically still pending. Such callbacks have the standard Pepper
  37 // callback semantics. Execution (i.e., completion) of callbacks happens through
  38 // objects of subclasses of |TrackedCallback|. Two things are ensured: (1) that
  39 // the callback is executed at most once, and (2) once a callback is marked to
  40 // be aborted, any subsequent completion is abortive (even if a non-abortive
  41 // completion had previously been scheduled).
  42 //
  43 // The details of non-abortive completion depend on the type of callback (e.g.,
  44 // different parameters may be required), but basic abort functionality is core.
  45 // The ability to post aborts is needed in many situations to ensure that the
  46 // plugin is not re-entered into. (Note that posting a task to just run
  47 // |Abort()| is different and not correct; calling |PostAbort()| additionally
  48 // guarantees that all subsequent completions will be abortive.)
  49 //
  50 // This class is reference counted so that different things can hang on to it,
  51 // and not worry too much about ensuring Pepper callback semantics. Note that
  52 // the "owning" |CallbackTracker| will keep a reference until the callback is
  53 // completed.
  54 //
  55 // Subclasses must do several things:
  56 //  - They must ensure that the callback is executed at most once (by looking at
  57 //    |completed()| before running the callback).
  58 //  - They must ensure that the callback is run abortively if it is marked as to
  59 //    be aborted (by looking at |aborted()| before running the callback).
  60 //  - They must call |MarkAsCompleted()| immediately before actually running the
  61 //    callback; see the comment for |MarkAsCompleted()| for a caveat.
  62 class PPAPI_SHARED_EXPORT TrackedCallback
  63     : public base::RefCountedThreadSafe<TrackedCallback> {
  64  public:
  65   // Create a tracked completion callback and register it with the tracker. The
  66   // resource pointer is not stored. If |resource| is NULL, this callback will
  67   // not be added to the callback tracker.
  68   TrackedCallback(Resource* resource, const PP_CompletionCallback& callback);
  69
  70   // These run the callback in an abortive manner, or post a task to do so (but
  71   // immediately marking the callback as to be aborted).
  72   void Abort();
  73   void PostAbort();
  74
  75   // Run the callback with the given result. If the callback had previously been
  76   // marked as to be aborted (by |PostAbort()|), |result| will be ignored and
  77   // the callback will be run with result |PP_ERROR_ABORTED|.
  78   //
  79   // Run() will invoke the call immediately, if invoked from the target thread
  80   // (as determined by target_loop_). If invoked on a different thread, the
  81   // callback will be scheduled to run later on target_loop_.
  82   void Run(int32_t result);
  83   // PostRun is like Run(), except it guarantees that the callback will be run
  84   // later. In particular, if you invoke PostRun on the same thread on which the
  85   // callback is targeted to run, it will *not* be run immediately.
  86   void PostRun(int32_t result);
  87
  88   // A task to perform cleanup or write output parameters before the callback
  89   // returns a result to the plugin. The |result| parameter has the result so
  90   // far, e.g. whether the callback has been aborted. If the callback hasn't
  91   // been aborted the return value of the task will become the callback result.
  92   // The task is always called on the same thread as the callback to the plugin.
  93   typedef base::Callback<int32_t(int32_t /* result */)> CompletionTask;
  94
  95   // Sets a task that is run just before calling back into the plugin. This
  96   // should only be called once.
  97   void set_completion_task(const CompletionTask& completion_task);
  98
  99   // Returns the ID of the resource which "owns" the callback, or 0 if the
 100   // callback is not associated with any resource.
 101   PP_Resource resource_id() const { return resource_id_; }
 102
 103   // Returns true if the callback was completed (possibly aborted).
 104   bool completed() const { return completed_; }
 105
 106   // Returns true if the callback was or should be aborted; this will be the
 107   // case whenever |Abort()| or |PostAbort()| is called before a non-abortive
 108   // completion.
 109   bool aborted() const { return aborted_; }
 110
 111   // Returns true if this is a blocking callback.
 112   bool is_blocking() { return !callback_.func; }
 113
 114   MessageLoopShared* target_loop() const { return target_loop_.get(); }
 115
 116   // Determines if the given callback is pending. A callback is pending if it
 117   // has not completed and has not been aborted. When receiving a plugin call,
 118   // use this to detect if |callback| represents an operation in progress. When
 119   // finishing a plugin call, use this to determine whether to write 'out'
 120   // params and Run |callback|.
 121   // NOTE: an aborted callback has not necessarily completed, so a false result
 122   // doesn't imply that the callback has completed.
 123   // As a convenience, if |callback| is null, this returns false.
 124   static bool IsPending(const scoped_refptr<TrackedCallback>& callback);
 125
 126   // Helper to determine if the given callback is scheduled to run on another
 127   // message loop.
 128   static bool IsScheduledToRun(const scoped_refptr<TrackedCallback>& callback);
 129
 130  protected:
 131   bool is_required() {
 132     return (callback_.func &&
 133             !(callback_.flags & PP_COMPLETIONCALLBACK_FLAG_OPTIONAL));
 134   }
 135   bool is_optional() {
 136     return (callback_.func &&
 137             (callback_.flags & PP_COMPLETIONCALLBACK_FLAG_OPTIONAL));
 138   }
 139   bool has_null_target_loop() const { return target_loop_.get() == NULL; }
 140
 141  private:
 142   // TrackedCallback and EnterBase manage dealing with how to invoke callbacks
 143   // appropriately. Pepper interface implementations and proxies should not have
 144   // to check the type of callback, block, or mark them complete explicitly.
 145   friend class ppapi::thunk::subtle::EnterBase;
 146
 147   // Block until the associated operation has completed. Returns the result.
 148   // This must only be called on a non-main thread on a blocking callback.
 149   int32_t BlockUntilComplete();
 150
 151   // Mark this object as complete and remove it from the tracker. This must only
 152   // be called once. Note that running this may result in this object being
 153   // deleted (so keep a reference if it'll still be needed).
 154   void MarkAsCompleted();
 155
 156   // This class is ref counted.
 157   friend class base::RefCountedThreadSafe<TrackedCallback>;
 158   virtual ~TrackedCallback();
 159
 160   // Flag used by |PostAbort()| and |PostRun()| to check that we don't schedule
 161   // the callback more than once.
 162   bool is_scheduled_;
 163
 164   scoped_refptr<CallbackTracker> tracker_;
 165   PP_Resource resource_id_;
 166   bool completed_;
 167   bool aborted_;
 168   PP_CompletionCallback callback_;
 169
 170   // Task to run just before calling back into the plugin.
 171   CompletionTask completion_task_;
 172
 173   // The MessageLoopShared on which this callback should be run. This will be
 174   // NULL if we're in-process.
 175   scoped_refptr<MessageLoopShared> target_loop_;
 176
 177   int32_t result_for_blocked_callback_;
 178   // Used for pausing/waking the blocked thread if this is a blocking completion
 179   // callback. Note that in-process, there is no lock, blocking callbacks are
 180   // not allowed, and therefore this pointer will be NULL.
 181   scoped_ptr<base::ConditionVariable> operation_completed_condvar_;
 182
 183   DISALLOW_IMPLICIT_CONSTRUCTORS(TrackedCallback);
 184 };
 185
 186 }  // namespace ppapi
 187
 188 #endif  // PPAPI_SHARED_IMPL_TRACKED_CALLBACK_H_