Unify var tracking between webkit and the proxy.

ppapi/shared_impl/var_tracker.h

+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef PPAPI_SHARED_IMPL_VAR_TRACKER_H_
+#define PPAPI_SHARED_IMPL_VAR_TRACKER_H_
+
+#include "base/basictypes.h"
+#include "base/hash_tables.h"
+#include "base/memory/ref_counted.h"
+#include "ppapi/c/pp_var.h"
+
+namespace ppapi {
+
+class Var;
+
+// Tracks non-POD (refcounted) var objects held by a plugin.
+//
+// The tricky part is the concept of a "tracked object". These are only
+// necessary in the plugin side of the proxy when running out of process. A
+// tracked object is one that the plugin is aware of, but doesn't hold a
+// reference to. This will happen when the plugin is passed an object as an
+// argument from the host (renderer) as an input argument to a sync function,
+// but where ownership is not passed.
+//
+// This class maintains the "track_with_no_reference_count" but doesn't do
+// anything with it other than call virtual functions. The interesting parts
+// are added by the PluginObjectVar derived from this class.
+class VarTracker {
+ public:
+  VarTracker();
+  virtual ~VarTracker();
+
+  // Called by the Var object to add a new var to the tracker.
+  int32 AddVar(Var* var);
+
+  // Looks up a given var and returns a reference to the Var if it exists.
+  // Returns NULL if the var type is not an object we track (POD) or is
+  // invalid.
+  Var* GetVar(int32 var_id) const;
+  Var* GetVar(const PP_Var& var) const;
+
+  // Increases a previously-known Var ID's refcount, returning true on success,
+  // false if the ID is invalid. The PP_Var version returns true and does
+  // nothing for non-refcounted type vars.
+  bool AddRefVar(int32 var_id);
+  bool AddRefVar(const PP_Var& var);
+
+  // Decreases the given Var ID's refcount, returning true on success, false if
+  // the ID is invalid or if the refcount was already 0. The PP_Var version
+  // returns true and does nothing for non-refcounted type vars.

[dmichael (off chromium), 2011/08/08 22:13:59]

Maybe mention the Var is deleted if ref count goes to 0?

+  bool ReleaseVar(int32 var_id);
+  bool ReleaseVar(const PP_Var& var);
+
+ protected:
+  struct VarInfo {
+    VarInfo();
+    VarInfo(Var* v, int input_ref_count);
+
+    scoped_refptr<Var> var;
+
+    // Explicit reference count. This value is affected by the renderer calling
+    // AddRef and Release. A nonzero value here is represented by a single
+    // reference in the host on our behalf (this reduces IPC traffic).
+    int ref_count;
+
+    // Tracked object count (see class comment above).
+    //
+    // "TrackObjectWithNoReference" might be called recursively in rare cases.
+    // For example, say the host calls a plugin function with an object as an
+    // argument, and in response, the plugin calls a host function that then
+    // calls another (or the same) plugin function with the same object.
+    //
+    // This value tracks the number of calls to TrackObjectWithNoReference so
+    // we know when we can stop tracking this object.
+    int track_with_no_reference_count;
+  };
+  typedef base::hash_map<int32, VarInfo> VarMap;
+
+  // Implementation of AddVar that allows the caller to specify whether the
+  // initial refcount of the added object will be 0 or 1.
+  //
+  // Overridden in the plugin proxy to do additional object tracking.
+  virtual int32 AddVarInternal(Var* var, bool take_ref);
+
+  // Convenience functions for doing lookups into the live_vars_ map.
+  VarMap::iterator GetLiveVar(int32 id);
+  VarMap::iterator GetLiveVar(const PP_Var& var);
+  VarMap::const_iterator GetLiveVar(const PP_Var& var) const;
+
+  // Returns true if the given vartype is refcounted and has associated objects
+  // (it's not POD).
+  bool IsVarTypeRefcounted(PP_VarType type) const;
+
+  // Called when AddRefVar increases a "tracked" ProxyObject's refcount from
+  // zero to one. In the plugin side of the proxy, we need to send some
+  // messages to the host. In the host side, this should never be called since
+  // there are no proxy objects.

[dmichael (off chromium), 2011/08/08 22:13:59]

optional suggest: You could have a member on this base class indicating if
you're in the host or not, just to do DCHECKs in these methods that only do
stuff in the plugin process.

[brettw, 2011/08/09 17:08:09]

The implementation of this function is actually NOTREACHED().

[dmichael (off chromium), 2011/08/09 19:16:48]

Missed that; perfect, thanks.

+  virtual void TrackedObjectGettingOneRef(VarMap::const_iterator iter);
+
+  // Called when ReleaseVar decreases a object's refcount from one to zero. It
+  // may still be "tracked" (has a "track_with_no_reference_count") value. In
+  // the plugin side of the proxy, we need to tell the host that we no longer
+  // have a reference. In the host side, this should never be called since
+  // there are no proxy objects.
+  virtual void ObjectGettingZeroRef(VarMap::iterator iter);
+
+  // Called when an object may have had its refcount or
+  // track_with_no_reference_count value decreased. If the object has neither
+  // refs anymore, this will remove it and return true. Returns false if it's
+  // still alive.
+  //
+  // Overridden by the PluginVarTracker to also clean up the host info map.
+  virtual bool DeleteObjectInfoIfNecessary(VarMap::iterator iter);
+
+  VarMap live_vars_;
+
+  // Last assigned var ID.
+  int32 last_var_id_;
+
+  DISALLOW_COPY_AND_ASSIGN(VarTracker);
+};
+
+}  // namespace ppapi
+
+#endif  // PPAPI_SHARED_IMPL_VAR_TRACKER_H_