Architecture for cross-process memory notification suppressing

content/browser/devtools/protocol/memory_handler.cc

+// Copyright 2015 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/devtools/protocol/memory_handler.h"
+
+#include "base/bind.h"
+#include "content/browser/memory/memory_message_filter.h"
+
+namespace content {
+namespace devtools {
+namespace memory {
+
+MemoryHandler::MemoryHandler() {}
+
+MemoryHandler::~MemoryHandler() {}
+
+MemoryHandler::Response MemoryHandler::SetNotificationsSuppressed(
+    bool suppressed) {
+  content::memory::MemoryMessageFilter::
+      SendSetNotificationsSuppressedToAllProcesses(suppressed);
+  return Response::OK();

[Sami, 2015/09/08 18:06:56]

Is there ever a need to wait for this to complete in all processes before
proceeding (e.g., benchmarks)?

[petrcermak, 2015/09/11 10:43:50]

Unfortunately, there is no way to get a callback when all memory pressure
listeners are finished (this would require a tremendous amount of plumbing
because it triggers a v8 GC, which in turn triggers a minor Blink GC, which then
schedules a major GC, ...), so even if we waited for all processes to handle the
IPC request, it wouldn't actually mean much. Therefore, I think it's better to
return immediately for simplicity and also performance (e.g. no need to store
and post tasks in the browser).

[Sami, 2015/09/11 11:37:42]

Like we discussed, I only meant waiting until the 'inhibit' bit has propagated
to all processes. Activating tracing after toggling this bit will force
synchronization as a side effect, so this isn't strictly required.

[petrcermak, 2015/09/14 12:46:22]

I added ack messages from child processes to address this (even if it is not
strictly necessary).

+}
+
+}  // namespace tracing
+}  // namespace devtools
+}  // namespace content