Broadcast NotifyTimezoneChange to all RenderProcessHosts when the system time zone changes

content/browser/time_zone_monitor_linux.cc

+// Copyright 2014 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 "content/browser/time_zone_monitor.h"
+
+#include <stdlib.h>
+
+#include <vector>
+
+#include "base/basictypes.h"
+#include "base/bind.h"
+#include "base/files/file_path.h"
+#include "base/files/file_path_watcher.h"
+#include "base/memory/ref_counted.h"
+#include "base/stl_util.h"
+#include "content/public/browser/browser_thread.h"
+
+#if !defined(OS_CHROMEOS)
+
+namespace content {
+
+namespace {
+class TimeZoneMonitorLinuxImpl;
+}  // namespace
+
+class TimeZoneMonitorLinux : public TimeZoneMonitor {
+ public:
+  TimeZoneMonitorLinux();
+  virtual ~TimeZoneMonitorLinux();
+
+  void NotifyRenderersFromImpl() {
+    NotifyRenderers();
+  }
+
+ private:
+  scoped_refptr<TimeZoneMonitorLinuxImpl> impl_;
+
+  DISALLOW_COPY_AND_ASSIGN(TimeZoneMonitorLinux);
+};
+
+namespace {
+
+// FilePathWatcher needs to run on the FILE thread, but TimeZoneMonitor runs
+// on the UI thread. TimeZoneMonitorLinuxImpl is the bridge between these
+// threads.
+class TimeZoneMonitorLinuxImpl
+    : public base::RefCountedThreadSafe<TimeZoneMonitorLinuxImpl> {
+ public:
+  explicit TimeZoneMonitorLinuxImpl(TimeZoneMonitorLinux* owner)
+      : base::RefCountedThreadSafe<TimeZoneMonitorLinuxImpl>(),
+        file_path_watchers_(),
+        owner_(owner) {

[jln (very slow on Chromium), 2014/04/29 22:57:47]

Do you want to DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI)) in the
constructor and the destructor as well?

[Mark Mentovai, 2014/04/30 03:52:24]

jln wrote:
Sure, done.

[Mark Mentovai, 2014/04/30 03:55:41]

jln wrote:
Well, I couldn’t do the destructor, because this class is reference-counted,
references may be held on the FILE thread, and we can’t be positive that the
last reference will be released on any thread in particular.

[jln (DO NOT USE THIS), 2014/04/30 05:46:36]

Ahh right, good point! And of course it's still fine: the destructor can indeed
run on any thread, as long as nothing is accessing owner_ or file_path_watchers_
which is guaranteed by the very fact that the destructor is being run.

+    BrowserThread::PostTask(
+        BrowserThread::FILE,
+        FROM_HERE,
+        base::Bind(&TimeZoneMonitorLinuxImpl::StartWatchingOnFileThread, this));
+  }
+
+  void StopWatching() {
+    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+    owner_ = NULL;
+    BrowserThread::PostTask(
+        BrowserThread::FILE,
+        FROM_HERE,
+        base::Bind(&TimeZoneMonitorLinuxImpl::StopWatchingOnFileThread, this));
+  }
+
+ private:
+  friend class base::RefCountedThreadSafe<TimeZoneMonitorLinuxImpl>;
+
+  ~TimeZoneMonitorLinuxImpl() {
+    DCHECK(!owner_);
+    STLDeleteElements(&file_path_watchers_);
+  }
+
+  void StartWatchingOnFileThread() {
+    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+
+    // There is no true standard for where time zone information is actually
+    // stored. glibc uses /etc/localtime, uClibc uses /etc/TZ, and some older
+    // systems store the name of the time zone file within /usr/share/zoneinfo
+    // in /etc/timezone. Different libraries and custom builds may mean that
+    // still more paths are used. Just watch all three of these paths, because
+    // false positives are harmless, assuming the false positive rate is
+    // reasonable.
+    const char* kFilesToWatch[] = {
+      "/etc/localtime",
+      "/etc/timezone",
+      "/etc/TZ",
+    };
+
+    for (size_t index = 0; index < arraysize(kFilesToWatch); ++index) {
+      file_path_watchers_.push_back(new base::FilePathWatcher());
+      file_path_watchers_.back()->Watch(
+          base::FilePath(kFilesToWatch[index]),
+          false,
+          base::Bind(&TimeZoneMonitorLinuxImpl::OnTimeZoneFileChanged, this));
+    }
+  }
+
+  void StopWatchingOnFileThread() {
+    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+    STLDeleteElements(&file_path_watchers_);
+  }
+
+  void OnTimeZoneFileChanged(const base::FilePath& path, bool error) {
+    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+    BrowserThread::PostTask(
+        BrowserThread::UI,
+        FROM_HERE,
+        base::Bind(&TimeZoneMonitorLinuxImpl::OnTimeZoneFileChangedOnUIThread,
+                   this));
+  }
+
+  void OnTimeZoneFileChangedOnUIThread() {
+    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+    if (owner_) {
+      owner_->NotifyRenderersFromImpl();
+    }
+  }
+
+  std::vector<base::FilePathWatcher*> file_path_watchers_;
+  TimeZoneMonitorLinux* owner_;
+
+  DISALLOW_COPY_AND_ASSIGN(TimeZoneMonitorLinuxImpl);
+};
+
+}  // namespace
+
+TimeZoneMonitorLinux::TimeZoneMonitorLinux()
+    : TimeZoneMonitor(),
+      impl_() {
+  // If the TZ environment variable is set, its value specifies the time zone
+  // specification, and it's pointless to monitor any files in /etc for
+  // changes because such changes would have no effect on the TZ environment
+  // variable and thus the interpretation of the local time zone in the
+  // or renderer processes.
+  //
+  // The system-specific format for the TZ environment variable beginning with
+  // a colon is implemented by glibc as the path to a time zone data file, and
+  // it would be possible to monitor this file for changes if a TZ variable of
+  // this format was encountered, but this is not necessary: when loading a
+  // time zone specification in this way, glibc does not reload the file when
+  // it changes, so it's pointless to respond to a notification that it has
+  // changed.
+  if (!getenv("TZ")) {
+    impl_ = new TimeZoneMonitorLinuxImpl(this);
+  }
+}
+
+TimeZoneMonitorLinux::~TimeZoneMonitorLinux() {
+  if (impl_) {
+    impl_->StopWatching();
+  }
+}
+
+// static
+scoped_ptr<TimeZoneMonitor> TimeZoneMonitor::Create() {
+  return scoped_ptr<TimeZoneMonitor>(new TimeZoneMonitorLinux());
+}
+
+}  // namespace content
+
+#endif  // !OS_CHROMEOS