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;
+
+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.
+  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;
+  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)
+
+  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::UnsafeReset() {
+  DCHECK(g_after_startup_tasks.Get().empty());
+  if (!IsBrowserStartupComplete())
+    return;
+  g_startup_complete_flag.Get().UnsafeReset();

[michaeln, 2015/04/06 23:12:22]

Another (better?) option here would be to reset the lazy instance to put it back
to the unallocated state.

+  DCHECK(!IsBrowserStartupComplete());
+}