Refactor FileBasedPolicyProvider, introduce AsynchronousPolicyProvider.

chrome/browser/policy/file_based_policy_loader.cc

+// Copyright (c) 2010 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/policy/file_based_policy_loader.h"
+
+namespace {
+
+// Amount of time we wait for the files on disk to settle before trying to load
+// them. This alleviates the problem of reading partially written files and
+// makes it possible to batch quasi-simultaneous changes.
+const int kSettleIntervalSeconds = 5;
+
+// The time interval for rechecking policy. This is our fallback in case the
+// delegate never reports a change to the ReloadObserver.
+const int kReloadIntervalMinutes = 15;
+
+}
+
+namespace policy {
+
+FileBasedPolicyLoader::FileBasedPolicyLoader(
+    FileBasedPolicyProvider::ProviderDelegate* provider_delegate)
+    : AsynchronousPolicyLoader(provider_delegate),
+      config_file_path_(provider_delegate->config_file_path()),
+      reload_task_(NULL),
+      reload_interval_(base::TimeDelta::FromMinutes(kReloadIntervalMinutes)),
+      settle_interval_(base::TimeDelta::FromSeconds(kSettleIntervalSeconds)) {
+}
+
+class FileBasedPolicyWatcherDelegate : public FilePathWatcher::Delegate {
+ public:
+  explicit FileBasedPolicyWatcherDelegate(
+      scoped_refptr<FileBasedPolicyLoader> loader)
+      : loader_(loader) {}
+  virtual ~FileBasedPolicyWatcherDelegate() {}
+
+  // FilePathWatcher::Delegate implementation:
+  void OnFilePathChanged(const FilePath& path) {
+    loader_->OnFilePathChanged(path);
+  }
+
+  void OnError() {
+    loader_->OnError();
+  }
+
+ private:
+  scoped_refptr<FileBasedPolicyLoader> loader_;
+  DISALLOW_COPY_AND_ASSIGN(FileBasedPolicyWatcherDelegate);
+};
+
+void FileBasedPolicyLoader::Init() {
+  AsynchronousPolicyLoader::Init();
+
+  // Initialization can happen early when the file thread is not yet available,
+  // but the watcher's initialization must be done on the file thread. Posting
+  // to a to the file directly before the file thread is initialized will cause
+  // the task to be forgotten. Instead, post a task to the ui thread to delay
+  // the remainder of initialization until threading is fully initialized.
+  BrowserThread::PostTask(
+      BrowserThread::FILE, FROM_HERE,
+      NewRunnableMethod(this,
+                        &FileBasedPolicyLoader::InitAfterFileThreadAvailable));
+}
+
+void FileBasedPolicyLoader::Stop() {
+  AsynchronousPolicyLoader::Stop();
+  BrowserThread::PostTask(
+      BrowserThread::FILE, FROM_HERE,
+      NewRunnableMethod(this, &FileBasedPolicyLoader::StopOnFileThread));
+}
+
+void FileBasedPolicyLoader::OnFilePathChanged(
+    const FilePath& path) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+  Reload();
+}
+
+void FileBasedPolicyLoader::OnError() {
+  LOG(ERROR) << "FilePathWatcher on " << config_file_path().value()
+             << " failed.";
+}
+
+void FileBasedPolicyLoader::Reload() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+
+  if (!delegate())
+    return;
+
+  // Check the directory time in order to see whether a reload is required.
+  base::TimeDelta delay;
+  base::Time now = base::Time::Now();
+  if (!IsSafeToReloadPolicy(now, &delay)) {
+    ScheduleReloadTask(delay);
+    return;
+  }
+
+  // Load the policy definitions.
+  scoped_ptr<DictionaryValue> new_policy(delegate()->Load());
+
+  // Check again in case the directory has changed while reading it.
+  if (!IsSafeToReloadPolicy(now, &delay)) {
+    ScheduleReloadTask(delay);
+    return;
+  }
+
+  PostUpdatePolicyTask(new_policy.release());
+
+  ScheduleFallbackReloadTask();
+}
+
+void FileBasedPolicyLoader::InitAfterFileThreadAvailable() {
+  if (provider()) {
+    BrowserThread::PostTask(
+        BrowserThread::FILE, FROM_HERE,
+        NewRunnableMethod(this, &FileBasedPolicyLoader::InitWatcher));
+
+    ScheduleFallbackReloadTask();
+  }
+}
+
+void FileBasedPolicyLoader::InitWatcher() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+  watcher_.reset(new FilePathWatcher);
+  if (!config_file_path().empty() &&
+      !watcher_->Watch(config_file_path(),
+                       new FileBasedPolicyWatcherDelegate(this))) {
+    OnError();
+  }
+
+  // There might have been changes to the directory in the time between
+  // construction of the loader and initialization of the watcher. Call reload
+  // to detect if that is the case.
+  Reload();
+}
+
+void FileBasedPolicyLoader::StopOnFileThread() {
+  watcher_.reset();
+  if (reload_task_) {
+    reload_task_->Cancel();
+    reload_task_ = NULL;
+  }
+}
+
+void FileBasedPolicyLoader::ScheduleReloadTask(
+    const base::TimeDelta& delay) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+
+  if (reload_task_)
+    reload_task_->Cancel();
+
+  reload_task_ =
+      NewRunnableMethod(this, &FileBasedPolicyLoader::ReloadFromTask);
+  BrowserThread::PostDelayedTask(BrowserThread::FILE, FROM_HERE, reload_task_,
+                                 delay.InMilliseconds());
+}
+
+void FileBasedPolicyLoader::ScheduleFallbackReloadTask() {
+  // As a safeguard in case that the load delegate failed to timely notice a
+  // change in policy, schedule a reload task that'll make us recheck after a
+  // reasonable interval.
+  ScheduleReloadTask(reload_interval_);
+}
+
+void FileBasedPolicyLoader::ReloadFromTask() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+
+  // Drop the reference to the reload task, since the task might be the only
+  // referer that keeps us alive, so we should not Cancel() it.
+  reload_task_ = NULL;
+
+  Reload();
+}
+
+bool FileBasedPolicyLoader::IsSafeToReloadPolicy(
+    const base::Time& now,
+    base::TimeDelta* delay) {
+  DCHECK(delay);
+
+  // A null modification time indicates there's no data.
+  FileBasedPolicyProvider::ProviderDelegate* provider_delegate =
+      static_cast<FileBasedPolicyProvider::ProviderDelegate*>(delegate());
+  base::Time last_modification(provider_delegate->GetLastModification());
+  if (last_modification.is_null())
+    return true;
+
+  // If there was a change since the last recorded modification, wait some more.
+  if (last_modification != last_modification_file_) {
+    last_modification_file_ = last_modification;
+    last_modification_clock_ = now;
+    *delay = settle_interval_;
+    return false;
+  }
+
+  // Check whether the settle interval has elapsed.
+  base::TimeDelta age = now - last_modification_clock_;
+  if (age < settle_interval_) {
+    *delay = settle_interval_ - age;
+    return false;
+  }
+
+  return true;
+}
+
+}  // namespace policy