Implement a poor man's PostAfterStartupTask() function.

chrome/browser/after_startup_task_utils.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 "chrome/browser/after_startup_task_utils.h"
+
+#include "base/lazy_instance.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/metrics/histogram_macros.h"
+#include "base/process/process_info.h"
+#include "base/rand_util.h"
+#include "base/synchronization/cancellation_flag.h"
+#include "base/task_runner.h"
+#include "base/tracked_objects.h"
+#include "chrome/browser/ui/browser.h"
+#include "chrome/browser/ui/browser_iterator.h"
+#include "chrome/browser/ui/tabs/tab_strip_model.h"
+#include "content/public/browser/browser_thread.h"
+#include "content/public/browser/render_frame_host.h"
+#include "content/public/browser/web_contents.h"
+#include "content/public/browser/web_contents_observer.h"
+
+using content::BrowserThread;
+using content::WebContents;
+using content::WebContentsObserver;
+using StartupCompleteFlag = base::CancellationFlag;

[Nico, 2015/04/09 20:10:15]

This is used in a single place. Why is this useful? Why not write
base::CancellationFlag in that one place directly?

[michaeln, 2015/04/09 21:48:39]

This should help tip readers off to the fact that its not being used as a
cancellation flag. An earlier review comment was something like, 'its weird to
be using a cancellation flag here, but it does exactly what we want'. It might
be nice to rename the base class to something more generic, SettableFlag?

+
+namespace {
+
+struct AfterStartupTask {
+  AfterStartupTask(const tracked_objects::Location& from_here,
+                   const scoped_refptr<base::TaskRunner>& task_runner,
+                   const base::Closure& task)
+      : from_here(from_here), task_runner(task_runner), task(task) {}
+  ~AfterStartupTask() {}
+
+  const tracked_objects::Location from_here;
+  const scoped_refptr<base::TaskRunner> task_runner;
+  const base::Closure task;
+};
+
+// The flag may be read on any thread, but must only be set on the UI thread.
+base::LazyInstance<StartupCompleteFlag>::Leaky g_startup_complete_flag;
+
+// The queue may only be accessed on the UI thread.
+base::LazyInstance<std::deque<AfterStartupTask*>>::Leaky g_after_startup_tasks;
+
+bool IsBrowserStartupComplete() {
+  // Be sure to allocate the flag on the main thread.

[Nico, 2015/04/09 20:10:15]

(i found this comment confusing. i get it now, but it took me a bit. no
allocation is done in this function.)

[michaeln, 2015/04/09 21:48:39]

Done

how about 'initialize the lazyinstance on the main thread since the flag may
only be set on initializing thread'

+  if (g_startup_complete_flag == nullptr)
+    return false;
+  return g_startup_complete_flag.Get().IsSet();
+}
+
+void RunTask(scoped_ptr<AfterStartupTask> queued_task) {
+  // We're careful to delete the caller's |task| on the target runner's thread.
+  DCHECK(queued_task->task_runner->RunsTasksOnCurrentThread());
+  queued_task->task.Run();
+}
+
+void ScheduleTask(scoped_ptr<AfterStartupTask> queued_task) {
+  // Spread their execution over a brief time.
+  const int kMinDelay = 0;
+  const int kMaxDelay = 10;

[Nico, 2015/04/09 20:10:15]

suffix name with unit (kMinDelaySec, kMaxDelaySec)

Do you have a sense of how many of these tasks we'll enqueue?

[michaeln, 2015/04/09 21:48:39]

Done.
I don't. I have in mind a few things that may generate 10s of tasks, as for
other uses, idk. An uma stat is in place to keep an eye on that number.

+  scoped_refptr<base::TaskRunner> target_runner = queued_task->task_runner;
+  tracked_objects::Location from_here = queued_task->from_here;
+  target_runner->PostDelayedTask(
+      from_here, base::Bind(&RunTask, base::Passed(queued_task.Pass())),
+      base::TimeDelta::FromSeconds(base::RandInt(kMinDelay, kMaxDelay)));
+}
+
+void QueueTask(scoped_ptr<AfterStartupTask> queued_task) {
+  if (!BrowserThread::CurrentlyOn(BrowserThread::UI)) {
+    BrowserThread::PostTask(
+        BrowserThread::UI, FROM_HERE,
+        base::Bind(QueueTask, base::Passed(queued_task.Pass())));
+    return;
+  }
+
+  // The flag may have been set while the task to invoke this method
+  // on the UI thread was inflight.
+  if (IsBrowserStartupComplete()) {
+    ScheduleTask(queued_task.Pass());
+    return;
+  }
+  g_after_startup_tasks.Get().push_back(queued_task.release());
+}
+
+void SetBrowserStartupIsComplete() {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+#if defined(OS_MACOSX) || defined(OS_WIN) || defined(OS_LINUX)
+  // CurrentProcessInfo::CreationTime() is not available on all platforms.
+  const base::Time process_creation_time =
+      base::CurrentProcessInfo::CreationTime();
+  if (!process_creation_time.is_null()) {
+    UMA_HISTOGRAM_LONG_TIMES("AfterStartupTasks.DelayedUntilTime",
+                             base::Time::Now() - process_creation_time);
+  }
+#endif  // defined(OS_MACOSX) || defined(OS_WIN) || defined(OS_LINUX)
+  UMA_HISTOGRAM_COUNTS_10000("AfterStartupTasks.Count",
+                             g_after_startup_tasks.Get().size());
+  g_startup_complete_flag.Get().Set();
+  for (AfterStartupTask* queued_task : g_after_startup_tasks.Get())
+    ScheduleTask(make_scoped_ptr(queued_task));
+  g_after_startup_tasks.Get().clear();
+
+  // The shrink_to_fit() method is not available for all of our build targets.
+  std::deque<AfterStartupTask*>(g_after_startup_tasks.Get())
+      .swap(g_after_startup_tasks.Get());
+}
+
+// Observes the first visible page load and sets the startup complete
+// flag accordingly.
+class StartupObserver : public WebContentsObserver, public base::NonThreadSafe {
+ public:
+  StartupObserver() : weak_factory_(this) {}
+  ~StartupObserver() override { DCHECK(IsBrowserStartupComplete()); }
+
+  void Start();
+
+ private:
+  void OnStartupComplete() {
+    DCHECK(CalledOnValidThread());
+    SetBrowserStartupIsComplete();
+    delete this;
+  }
+
+  void OnFailsafeTimeout() { OnStartupComplete(); }
+
+  // WebContentsObserver overrides
+  void DidFinishLoad(content::RenderFrameHost* render_frame_host,
+                     const GURL& validated_url) override {
+    if (!render_frame_host->GetParent())
+      OnStartupComplete();
+  }
+
+  void DidFailLoad(content::RenderFrameHost* render_frame_host,
+                   const GURL& validated_url,
+                   int error_code,
+                   const base::string16& error_description) override {
+    if (!render_frame_host->GetParent())
+      OnStartupComplete();
+  }
+
+  void WebContentsDestroyed() override { OnStartupComplete(); }
+
+  base::WeakPtrFactory<StartupObserver> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(StartupObserver);
+};
+
+void StartupObserver::Start() {
+  // Signal completion quickly when there is no first page to load.
+  const int kShortDelaySecs = 3;
+  base::TimeDelta delay = base::TimeDelta::FromSeconds(kShortDelaySecs);
+
+#if !defined(OS_ANDROID)
+  WebContents* contents = nullptr;
+  for (chrome::BrowserIterator iter; !iter.done(); iter.Next()) {
+    contents = (*iter)->tab_strip_model()->GetActiveWebContents();
+    if (contents && contents->GetMainFrame() &&
+        contents->GetMainFrame()->GetVisibilityState() ==
+            blink::WebPageVisibilityStateVisible) {
+      break;
+    }
+  }
+
+  if (contents) {
+    // Give the page time to finish loading.
+    const int kLongerDelayMins = 3;
+    Observe(contents);
+    delay = base::TimeDelta::FromMinutes(kLongerDelayMins);
+  }
+#endif  // !defined(OS_ANDROID)

[Nico, 2015/04/09 20:10:15]

shouldn't we default to more than 3 unconditional seconds on android?

[michaeln, 2015/04/09 21:48:39]

i think android should probably monitor the initial page load too. the only
reason i'm not doing it in this cl is because ChromeBrowserMainExtraPartsMetrics
avoid observing the first page load on android (i'm not sure why).

for now, i'll bumped it up to an unconditional 10secs for OS_ANDROID

+
+  BrowserThread::PostDelayedTask(BrowserThread::UI, FROM_HERE,
+                                 base::Bind(&StartupObserver::OnFailsafeTimeout,
+                                            weak_factory_.GetWeakPtr()),
+                                 delay);
+}
+
+}  // namespace
+
+void AfterStartupTaskUtils::StartMonitoringStartup() {
+  // The observer is self-deleting.
+  (new StartupObserver)->Start();
+}
+
+void AfterStartupTaskUtils::PostTask(
+    const tracked_objects::Location& from_here,
+    const scoped_refptr<base::TaskRunner>& task_runner,
+    const base::Closure& task) {
+  if (IsBrowserStartupComplete()) {
+    task_runner->PostTask(from_here, task);
+    return;
+  }
+
+  scoped_ptr<AfterStartupTask> queued_task(
+      new AfterStartupTask(from_here, task_runner, task));
+  QueueTask(queued_task.Pass());
+}
+
+void AfterStartupTaskUtils::SetBrowserStartupIsComplete() {
+  ::SetBrowserStartupIsComplete();
+}
+
+bool AfterStartupTaskUtils::IsBrowserStartupComplete() {
+  return ::IsBrowserStartupComplete();
+}
+
+void AfterStartupTaskUtils::UnsafeResetForTesting() {
+  DCHECK(g_after_startup_tasks.Get().empty());
+  if (!IsBrowserStartupComplete())
+    return;
+  g_startup_complete_flag.Get().UnsafeResetForTesting();
+  DCHECK(!IsBrowserStartupComplete());
+}