Add the AsyncPolicyProvider and AsyncPolicyLoader

chrome/browser/policy/async_policy_loader.cc

+// Copyright (c) 2012 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/async_policy_loader.h"
+
+#include "base/bind.h"
+#include "base/bind_helpers.h"
+#include "base/file_path.h"
+#include "base/files/file_path_watcher.h"
+#include "chrome/browser/policy/policy_bundle.h"
+#include "content/public/browser/browser_thread.h"
+
+using base::Time;
+using base::TimeDelta;
+using content::BrowserThread;
+
+namespace policy {
+
+namespace {
+
+// Amount of time to 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 the fallback in case the
+// implementation never detects changes.
+const int kReloadIntervalSeconds = 15 * 60;
+
+// This delegate is owned by the FilePathWatcher. It lives in FILE and notifies
+// the AsyncPolicyLoader through the |reload_callback|, which is invalidated
+// when the AsyncPolicyLoader is deleted.

[Mattias Nissler (ping if slow), 2012/06/04 08:48:26]

Note: net/dns/file_path_watcher_wrapper.h does mostly the same thing (see
http://code.google.com/p/chromium/issues/detail?id=130610 for context). The root
issue here is that FilePathWatcher should be converted to new-style callbacks,
instead of everybody writing their own wrapper.

[Joao da Silva, 2012/06/04 14:05:06]

Moved this to FilePathWatcher in another CL.

+class FilePathWatcherDelegate : public base::files::FilePathWatcher::Delegate {
+ public:
+  explicit FilePathWatcherDelegate(const base::Closure& reload_callback)
+      : reload_callback_(reload_callback) {}
+
+  // FilePathWatcher::Delegate implementation.
+  virtual void OnFilePathChanged(const FilePath& path) OVERRIDE {
+    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+    reload_callback_.Run();
+  }
+
+  virtual void OnFilePathError(const FilePath& path) OVERRIDE {
+    DLOG(ERROR) << "FilePathWatcher error: " << path.value();
+  }
+
+ private:
+  virtual ~FilePathWatcherDelegate() {}
+
+  base::Closure reload_callback_;
+
+  DISALLOW_COPY_AND_ASSIGN(FilePathWatcherDelegate);
+};
+
+}  // namespace
+
+AsyncPolicyLoader::AsyncPolicyLoader()
+    : ALLOW_THIS_IN_INITIALIZER_LIST(reload_weak_factory_(this)),
+      ALLOW_THIS_IN_INITIALIZER_LIST(watchers_weak_factory_(this)) {}
+
+AsyncPolicyLoader::~AsyncPolicyLoader() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+}
+
+base::Time AsyncPolicyLoader::LastModificationTime() {
+  return base::Time();
+}
+
+void AsyncPolicyLoader::Reload(bool force) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+
+  TimeDelta delay;
+  Time now = Time::Now();
+  // Check if there was a recent modification to the underlying files.
+  if (!force && !IsSafeToReload(now, &delay)) {
+    ScheduleNextReload(delay);
+    return;
+  }
+
+  scoped_ptr<PolicyBundle> bundle(Load());
+
+  // Check if there was a modification while reading.
+  if (!force && !IsSafeToReload(now, &delay)) {
+    ScheduleNextReload(delay);
+    return;
+  }
+
+  BrowserThread::PostTask(BrowserThread::UI, FROM_HERE,
+                          base::Bind(update_callback_, base::Passed(&bundle)));
+  ScheduleNextReload(TimeDelta::FromSeconds(kReloadIntervalSeconds));
+}
+
+void AsyncPolicyLoader::WatchPath(const FilePath& path) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+  base::files::FilePathWatcher* watcher = new base::files::FilePathWatcher();
+  base::Closure reload_callback =
+      base::Bind(&AsyncPolicyLoader::Reload,
+                 watchers_weak_factory_.GetWeakPtr(),
+                 false  /* force */);
+  if (watcher->Watch(path, new FilePathWatcherDelegate(reload_callback))) {

[Mattias Nissler (ping if slow), 2012/06/04 08:48:26]

no need for curlies

[Joao da Silva, 2012/06/04 14:05:06]

Done.

+    watchers_.push_back(watcher);
+  } else {
+    DLOG(ERROR) << "FilePathWatcher error adding watch: " << path.value();
+  }
+}
+
+scoped_ptr<PolicyBundle> AsyncPolicyLoader::InitialLoad() {
+  // This is the first load, early during startup. Use this to record the
+  // initial |last_modification_time_|, so that potential changes made before
+  // installing the watches can be detected.
+  last_modification_time_ = LastModificationTime();
+  return Load();
+}
+
+void AsyncPolicyLoader::Init(
+    const UpdateCallback& update_callback) {

[Mattias Nissler (ping if slow), 2012/06/04 08:48:26]

fits previous line

[Joao da Silva, 2012/06/04 14:05:06]

Done.

+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+  DCHECK(update_callback_.is_null());
+  DCHECK(!update_callback.is_null());
+  update_callback_ = update_callback;
+
+  InitOnFile();
+
+  // There might have been changes to the underlying files since the initial
+  // load and before the watchers have been created.
+  if (LastModificationTime() != last_modification_time_)
+    Reload(false);
+
+  // Start periodic refreshes.
+  ScheduleNextReload(TimeDelta::FromSeconds(kReloadIntervalSeconds));
+}
+
+void AsyncPolicyLoader::ScheduleNextReload(TimeDelta delay) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+  reload_weak_factory_.InvalidateWeakPtrs();
+  BrowserThread::PostDelayedTask(
+      BrowserThread::FILE, FROM_HERE,
+      base::Bind(&AsyncPolicyLoader::Reload,
+                  reload_weak_factory_.GetWeakPtr(),

[Mattias Nissler (ping if slow), 2012/06/04 08:48:26]

indentation

[Joao da Silva, 2012/06/04 14:05:06]

Done.

+                  false  /* force */),
+      delay);
+}
+
+bool AsyncPolicyLoader::IsSafeToReload(const Time& now, TimeDelta* delay) {
+  Time last_modification = LastModificationTime();
+  if (last_modification.is_null())
+    return true;
+
+  // If there was a change since the last recorded modification, wait some more.
+  TimeDelta kSettleInterval(TimeDelta::FromSeconds(kSettleIntervalSeconds));

[Mattias Nissler (ping if slow), 2012/06/04 08:48:26]

const

[Joao da Silva, 2012/06/04 14:05:06]

Done.

+  if (last_modification != last_modification_time_) {
+    last_modification_time_ = last_modification;
+    last_modification_clock_ = now;
+    *delay = kSettleInterval;
+    return false;
+  }
+
+  // Check whether the settle interval has elapsed.
+  base::TimeDelta age = now - last_modification_clock_;
+  if (age < kSettleInterval) {
+    *delay = kSettleInterval - age;
+    return false;
+  }
+
+  return true;
+}
+
+}  // namespace policy