Implements a monitor to watch for the browser hanging.

components/browser_watcher/window_hang_monitor_win.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 "components/browser_watcher/window_hang_monitor_win.h"
+
+#include "base/message_loop/message_loop.h"
+#include "base/win/message_window.h"
+
+namespace browser_watcher {
+
+namespace {
+
+const size_t kPingIntervalSeconds = 60;
+const size_t kHangTimeoutSeconds = 20;
+
+bool IsWindowValid(HWND window,
+                   const base::string16& window_name,
+                   base::ProcessId pid) {
+  // Validate the Window in two respects:
+  // 1. The window handle might have been re-assigned to a different window
+  //    from the time we found it to the point where we query for its owning
+  //    process.
+  // 2. The window handle might have been re-assigned to a different process
+  //    at any point after we found it.
+  if (window != base::win::MessageWindow::FindWindow(window_name)) {
+    // The window handle has been reassigned, bail.
+    return false;
+  }
+
+  // Re-do the process ID lookup.
+  DWORD new_process_id = 0;
+  DWORD thread_id = ::GetWindowThreadProcessId(window, &new_process_id);
+  if (thread_id == 0 || pid != new_process_id) {
+    // Another process has taken over the handle.
+    return false;
+  }
+
+  return true;
+}
+
+}  // namespace
+
+WindowHangMonitor::WindowHangMonitor(const WindowEventCallback& callback)
+    : callback_(callback),
+      window_(NULL),
+      outstanding_ping_(nullptr),
+      timer_(false /* don't retain user task */, false /* don't repeat */),
+      ping_interval_(base::TimeDelta::FromSeconds(kPingIntervalSeconds)),
+      hang_timeout_(base::TimeDelta::FromSeconds(kHangTimeoutSeconds)) {
+}
+
+WindowHangMonitor::~WindowHangMonitor() {
+  if (outstanding_ping_) {
+    // We have an outstanding ping, disable it and leak it intentionally as
+    // if the callback arrives eventually, it'll cause a use-after-free.
+    outstanding_ping_->monitor = nullptr;
+    outstanding_ping_ = nullptr;
+  }
+}
+
+bool WindowHangMonitor::Initialize(const base::string16& window_name) {
+  window_name_ = window_name;
+  timer_.SetTaskRunner(base::MessageLoop::current()->task_runner());
+
+  // This code is fraught with all kinds of races. As the purpose here is
+  // only monitoring, this code simply bails if any kind of race is encountered.
+  // Find the window to monitor by name.
+  window_ = base::win::MessageWindow::FindWindow(window_name);
+  if (window_ == NULL)
+    return false;
+
+  // Find and open the process owning this window.
+  DWORD process_id = 0;
+  DWORD thread_id = ::GetWindowThreadProcessId(window_, &process_id);
+  if (thread_id == 0 || process_id == 0) {
+    // The window has vanished or there was some other problem with the handle.
+    return false;
+  }
+
+  // Keep an open handle on the process to make sure the PID isn't reused.
+  window_process_ = base::Process::Open(process_id);
+  if (!window_process_.IsValid()) {
+    // The process may be at a different security level.
+    return false;
+  }
+
+  return MaybeSendPing();
+}
+
+void WindowHangMonitor::OnPongReceived(LRESULT lresult) {
+  // Outstanding, the window is not yet hung.

[erikwright (departed), 2015/03/25 18:57:21]

har har.

[Sigurður Ásgeirsson, 2015/03/25 19:56:52]

Acknowledged.

+  outstanding_ping_ = nullptr;
+}
+
+void WindowHangMonitor::SetPingIntervalForTesting(
+    base::TimeDelta ping_interval) {
+  ping_interval_ = ping_interval;
+}
+
+void WindowHangMonitor::SetHangTimeoutForTesting(base::TimeDelta hang_timeout) {
+  hang_timeout_ = hang_timeout;
+}
+
+void CALLBACK WindowHangMonitor::SendAsyncProc(HWND window,
+                                               UINT msg,
+                                               ULONG_PTR data,
+                                               LRESULT lresult) {
+  OutstandingPing* outstanding = reinterpret_cast<OutstandingPing*>(data);
+
+  // Delegate to the monitor if it's still around.
+  if (outstanding->monitor) {
+    outstanding->monitor->OnPongReceived(lresult);

[erikwright (departed), 2015/03/25 18:57:21]

Why the indirection? This is a (static) member method, it can set
outstanding->monitor->outstanding_ping_ to nullptr just fine.

[erikwright (departed), 2015/03/25 18:57:21]

why pass the lresult?

[Sigurður Ásgeirsson, 2015/03/25 19:56:52]

Yeah - indeed. I thought I'd have a use for it.

[Sigurður Ásgeirsson, 2015/03/25 19:56:53]

Done.

+  }
+
+  delete outstanding;

[erikwright (departed), 2015/03/25 18:57:21]

I'd maybe put this in OnPongReceived

[Sigurður Ásgeirsson, 2015/03/25 19:56:52]

This wants to be in the callback, as that way a late callback will clean up the
instance.

+}
+
+bool WindowHangMonitor::MaybeSendPing() {
+  DCHECK(window_process_.IsValid());

[erikwright (departed), 2015/03/25 18:57:21]

include logging.h

[Sigurður Ásgeirsson, 2015/03/25 19:56:53]

Done.

+  DCHECK(window_);
+  DCHECK(!outstanding_ping_);
+
+  if (!IsWindowValid(window_, window_name_, window_process_.Pid())) {
+    // The window is no longer valid, issue the callback.
+    callback_.Run(WINDOW_VANISHED);

[erikwright (departed), 2015/03/25 18:57:21]

include callback.h

[Sigurður Ásgeirsson, 2015/03/25 19:56:53]

Done.

+    return false;
+  }
+
+  // The window checks out, issue a ping against it. Set up all state ahead of
+  // time to allow for the possibility of the callback being invoked from within
+  // SendMessageCallback.
+  outstanding_ping_ = new OutstandingPing;
+  outstanding_ping_->monitor = this;
+
+  // Note that this is still racy to |window_| having been re-assigned, but
+  // the race is as small as we can make it, and the next attempt will re-try.
+  if (!::SendMessageCallback(window_, WM_NULL, 0, 0, &SendAsyncProc,
+                             reinterpret_cast<ULONG_PTR>(outstanding_ping_))) {
+    // Message sending failed, assume he window is no longer valid,

[erikwright (departed), 2015/03/25 18:57:21]

he -> the

[Sigurður Ásgeirsson, 2015/03/25 19:56:53]

Done.

+    // issue the callback and stop the polling.
+    delete outstanding_ping_;
+    outstanding_ping_ = nullptr;
+
+    callback_.Run(WINDOW_VANISHED);
+    return false;
+  }
+
+  // Issue the count-out callback.
+  timer_.Start(
+      FROM_HERE, hang_timeout_,
+      base::Bind(&WindowHangMonitor::OnHangTimeout, base::Unretained(this)));
+
+  return true;
+}
+
+void WindowHangMonitor::OnHangTimeout() {
+  DCHECK(window_process_.IsValid());
+  DCHECK(window_);
+
+  if (outstanding_ping_) {
+    // The ping is still outstanding, the window is hung or has vanished.
+    // Orphan the outstanding ping. If the callback arrives late, it will
+    // delete it, or if the callback never arrives it'll leak.
+    outstanding_ping_->monitor = NULL;
+    outstanding_ping_ = NULL;
+
+    if (!IsWindowValid(window_, window_name_, window_process_.Pid())) {
+      // The window vanished.
+      callback_.Run(WINDOW_VANISHED);
+    } else {
+      // The window hung.
+      callback_.Run(WINDOW_HUNG);
+    }
+  } else {
+    // No ping outstanding, window is not yet hung. Schedule the next retry.
+    timer_.Start(
+        FROM_HERE, hang_timeout_ - ping_interval_,
+        base::Bind(&WindowHangMonitor::OnRetryTimeout, base::Unretained(this)));
+  }
+}
+
+void WindowHangMonitor::OnRetryTimeout() {
+  MaybeSendPing();

[erikwright (departed), 2015/03/25 18:57:21]

why the indirection?

[Sigurður Ásgeirsson, 2015/03/25 19:56:52]

For readability - IMHO marginally clearer than to delegate straight to a
function whose only role in life is to reuse some implementation.

+}
+
+}  // namespace browser_watcher