Var serialization-related proxy stuff. This allows vars to be sent over IPC...

ppapi/proxy/plugin_var_serialization_rules.cc

+// Copyright (c) 2010 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.
+
+#include "ppapi/proxy/plugin_var_serialization_rules.h"
+
+#include "ppapi/proxy/plugin_var_tracker.h"
+
+namespace pp {
+namespace proxy {
+
+PluginVarSerializationRules::PluginVarSerializationRules(
+    PluginVarTracker* var_tracker)
+    : var_tracker_(var_tracker) {
+}
+
+PluginVarSerializationRules::~PluginVarSerializationRules() {
+}
+
+void PluginVarSerializationRules::SendCallerOwned(const PP_Var& var,
+                                                  std::string* str_val) {
+  // Nothing to do since we manage the refcount, other than retrieve the string
+  // to use for IPC.
+  if (var.type == PP_VARTYPE_STRING)
+    *str_val = var_tracker_->GetString(var);
+}
+
+PP_Var PluginVarSerializationRules::BeginReceiveCallerOwned(
+    const PP_Var& var,
+    const std::string* str_val) {
+  if (var.type == PP_VARTYPE_STRING) {
+    // Convert the string to the context of the current process.
+    PP_Var ret;
+    ret.type = PP_VARTYPE_STRING;
+    ret.value.as_id = var_tracker_->MakeString(*str_val);
+    return ret;
+  }
+
+  return var;
+}
+
+void PluginVarSerializationRules::EndReceiveCallerOwned(const PP_Var& var) {
+  if (var.type == PP_VARTYPE_STRING) {
+    // Destroy the string BeginReceiveCallerOwned created above.
+    var_tracker_->Release(var);
+  }
+}
+
+PP_Var PluginVarSerializationRules::ReceivePassRef(const PP_Var& var,
+                                                   const std::string& str_val) {
+  if (var.type == PP_VARTYPE_STRING) {
+    // Convert the string to the context of the current process.
+    PP_Var ret;
+    ret.type = PP_VARTYPE_STRING;
+    ret.value.as_id = var_tracker_->MakeString(str_val);
+    return ret;
+  }
+
+  // Overview of sending an object with "pass ref" from the browser to the
+  // plugin:
+  //                                  Example 1             Example 2
+  //                               Plugin   Browser      Plugin   Browser
+  // Before send                      3        2            0        1
+  // Browser calls BeginSendPassRef   3        2            0        1
+  // Plugin calls ReceivePassRef      4        1            1        1
+  // Browser calls EndSendPassRef     4        1            1        1
+  //
+  // In example 1 before the send, the plugin has 3 refs which are represented
+  // as one ref in the browser (since the plugin only tells the browser when
+  // it's refcount goes from 1 -> 0). The initial state is that the browser
+  // plugin code started to return a value, which means it gets another ref
+  // on behalf of the caller. This needs to be transferred to the plugin and
+  // folded in to its set of refs it maintains (with one ref representing all
+  // fo them in the browser).
+  if (var.type == PP_VARTYPE_OBJECT)
+    var_tracker_->ReceiveObjectPassRef(var);
+  return var;
+}
+
+void PluginVarSerializationRules::BeginSendPassRef(const PP_Var& var,
+                                                   std::string* str_val) {
+  // Overview of sending an object with "pass ref" from the plugin to the
+  // browser:
+  //                                  Example 1             Example 2
+  //                               Plugin   Browser      Plugin   Browser
+  // Before send                      3        1            1        1
+  // Plugin calls BeginSendPassRef    3        1            1        1
+  // Browser calls ReceivePassRef     3        2            1        2
+  // Plugin calls EndSendPassRef      2        2            0        1
+  //
+  // The plugin maintains one ref count in the browser on behalf of the
+  // entire ref count in the plugin. When the plugin refcount goes to 0, it
+  // will call the browser to deref the object. This is why in example 2
+  // transferring the object ref to the browser involves no net change in the
+  // browser's refcount.
+
+  if (var.type == PP_VARTYPE_STRING)
+    *str_val = var_tracker_->GetString(var);
+}
+
+void PluginVarSerializationRules::EndSendPassRef(const PP_Var& var) {
+  // See BeginSendPassRef for an example of why we release our ref here.
+  if (var.type == PP_VARTYPE_OBJECT)
+    var_tracker_->Release(var);
+}
+
+void PluginVarSerializationRules::ReleaseObjectRef(const PP_Var& var) {
+  var_tracker_->Release(var);
+}
+
+}  // namespace proxy
+}  // namespace pp