Tab Audio Capture: Browser-side connect/disconnect functionality.

content/browser/renderer_host/media/web_contents_capture_util.cc

+// Copyright (c) 2012 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 "content/browser/renderer_host/media/web_contents_capture_util.h"
+
+#include "base/basictypes.h"
+#include "base/string_number_conversions.h"
+#include "base/string_piece.h"
+#include "base/string_util.h"
+#include "content/public/browser/browser_thread.h"
+#include "content/public/browser/render_process_host.h"
+#include "content/public/browser/render_view_host.h"
+#include "content/public/browser/web_contents.h"
+
+namespace {
+
+const char kVirtualDeviceScheme[] = "virtual://";
+
+}  // namespace
+
+namespace content {
+
+// static
+bool WebContentsCaptureUtil::ExtractTabCaptureTarget(
+    const std::string& device_id_param,
+    int* render_process_id,
+    int* render_view_id) {
+  const std::string device_id = device_id_param.substr(
+      arraysize(kVirtualDeviceScheme) - 1, device_id_param.length());
+
+  const size_t sep_pos = device_id.find(':');
+  if (sep_pos == std::string::npos)
+    return false;
+
+  const base::StringPiece component1(device_id.data(), sep_pos);
+  const base::StringPiece component2(device_id.data() + sep_pos + 1,
+                                     device_id.length() - sep_pos - 1);
+
+  return (base::StringToInt(component1, render_process_id) &&
+          base::StringToInt(component2, render_view_id));
+}
+
+WebContentsCaptureUtil::RenderViewTracker::RenderViewTracker() {}
+
+WebContentsCaptureUtil::RenderViewTracker::~RenderViewTracker() {
+  DCHECK(!web_contents()) << "BUG: Still observering!";
+}
+
+void WebContentsCaptureUtil::RenderViewTracker::Start(
+    int render_process_id, int render_view_id,
+    const ChangeCallback& callback) {
+  {

[Alpha Left Google, 2012/11/26 22:59:59]

I still think this can be done without a lock:

Start(), Stop() and callback is accessed only on the IO thread. During Stop(),
callback is reset() on IO thread. When Lookup is completed it post a task back
to IO thread, it never touches callback on UI thread.

[miu, 2012/11/28 05:05:01]

Actually, that's not guaranteed.  The reason is because I intend to re-use this
class for WebContentsVideoCaptureDevice (common functionality).  WCVCD will not
be able to instantiate the RenderViewTracker from the IO thread.  In addition,
it will want to be called back on the UI thread (for simplicity).

This is what motivated the use of the lock_ around the callback_.  Also, I'm
making it the caller's responsibility to use media::BindToLoop() to make sure
the "change events" are posted back to the correct thread.

+    base::AutoLock guard(lock_);
+    callback_ = callback;
+  }
+  BrowserThread::PostTask(
+      BrowserThread::UI, FROM_HERE,
+      base::Bind(&RenderViewTracker::LookUpAndObserveWebContents, this,

[Alpha Left Google, 2012/11/26 22:59:59]

Use BindToLoop here such that LookUpAndObserveWebContents is called on IO
thread.

+                 render_process_id, render_view_id));
+}
+
+void WebContentsCaptureUtil::RenderViewTracker::Stop() {
+  {
+    base::AutoLock guard(lock_);
+    callback_.Reset();
+  }
+  BrowserThread::PostTask(
+      BrowserThread::UI, FROM_HERE,
+      base::Bind(&RenderViewTracker::Observe, this,
+                 static_cast<WebContents*>(NULL)));
+}
+
+void WebContentsCaptureUtil::RenderViewTracker::OnWebContentsChangeEvent() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+
+  WebContents* const wc = web_contents();
+  RenderViewHost* const rvh = wc ? wc->GetRenderViewHost() : NULL;
+  RenderProcessHost* const rph = rvh ? rvh->GetProcess() : NULL;
+
+  const int render_process_id = rph ? rph->GetID() : MSG_ROUTING_NONE;
+  const int render_view_id = rvh ? rvh->GetRoutingID() : MSG_ROUTING_NONE;
+
+  base::AutoLock guard(lock_);
+  if (!callback_.is_null()) {
+    callback_.Run(render_process_id, render_view_id);

[Alpha Left Google, 2012/11/26 22:59:59]

If you access |callback| only on IO thread you don't need this lock. In fact
because of BindToLoop() OnTargetChanged is called on IO thread anyway.

+  }
+}
+
+void WebContentsCaptureUtil::RenderViewTracker::LookUpAndObserveWebContents(
+    int render_process_id, int render_view_id) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+
+  RenderViewHost* const rvh =
+      RenderViewHost::FromID(render_process_id, render_view_id);
+  DVLOG_IF(1, !rvh) << "RenderViewHost::FromID("
+                    << render_process_id << ", " << render_view_id
+                    << ") returned NULL.";
+  Observe(rvh ? WebContents::FromRenderViewHost(rvh) : NULL);
+  DVLOG_IF(1, !web_contents())
+      << "WebContents::FromRenderViewHost(" << rvh << ") returned NULL.";
+
+  OnWebContentsChangeEvent();
+}
+
+void WebContentsCaptureUtil::RenderViewTracker::RenderViewReady() {
+  OnWebContentsChangeEvent();
+}
+
+void WebContentsCaptureUtil::RenderViewTracker::WebContentsDestroyed(
+    WebContents* web_contents) {
+  OnWebContentsChangeEvent();
+}
+
+}  // namespace content