Destroy the CDM asynchronously

media/blink/cdm_session_adapter.cc

 // Copyright 2014 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 "media/blink/cdm_session_adapter.h"
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
 #include "base/stl_util.h"
+#include "base/thread_task_runner_handle.h"
 #include "base/trace_event/trace_event.h"
 #include "media/base/cdm_factory.h"
 #include "media/base/cdm_key_information.h"
 #include "media/base/cdm_promise.h"
 #include "media/base/key_systems.h"
 #include "media/blink/webcontentdecryptionmodule_impl.h"
 #include "media/blink/webcontentdecryptionmodulesession_impl.h"
 #include "url/gurl.h"
 
 namespace media {
 
+namespace {
 const char kMediaEME[] = "Media.EME.";
 const char kDot[] = ".";
 const char kTimeToCreateCdmUMAName[] = "CreateCdmTime";
 
+void ReleaseCdm(scoped_refptr<MediaKeys> cdm) {
+  // |cdm| will be freed now.
+}
+
+}  // namespace
+
 CdmSessionAdapter::CdmSessionAdapter()
     : trace_id_(0), weak_ptr_factory_(this) {}
 
-CdmSessionAdapter::~CdmSessionAdapter() {}
+CdmSessionAdapter::~CdmSessionAdapter() {
+  // Freeing |cdm_| may take a while, so post a task to do it asynchronously.
+  // Note that freeing the CDM will cause any unfullfilled promises to be
+  // rejected, and that needs to be done outside of blink gc (which most
+  // likely triggered our destruction).
+  if (cdm_) {
+    base::ThreadTaskRunnerHandle::Get()->PostTask(
+        FROM_HERE, base::Bind(&ReleaseCdm, cdm_));

[xhwang, 2016/04/11 16:52:20]

nit: This can be done with MessageLoop::ReleaseSoon:

https://code.google.com/p/chromium/codesearch#chromium/src/base/message_loop/...

Though I don't really like the syntax using it (AddRef, take raw pointer etc).

+  }
+}
 
 void CdmSessionAdapter::CreateCdm(
     CdmFactory* cdm_factory,
     const std::string& key_system,
     const GURL& security_origin,
     const CdmConfig& cdm_config,
     scoped_ptr<blink::WebContentDecryptionModuleResult> result) {
   TRACE_EVENT_ASYNC_BEGIN0("media", "CdmSessionAdapter::CreateCdm",
                            ++trace_id_);
 
@@ skipping 185 matching lines @@
   // Note: This leaks memory, which is expected behavior.
   base::HistogramBase* histogram = base::Histogram::FactoryTimeGet(
       GetKeySystemUMAPrefix() + kTimeToCreateCdmUMAName,
       base::TimeDelta::FromMilliseconds(1), base::TimeDelta::FromSeconds(10),
       50, base::HistogramBase::kUmaTargetedHistogramFlag);
 
   histogram->AddTime(time);
 }
 
 }  // namespace media