Remove the dependence on BrowserThread::FILE for

net/proxy/proxy_config_service_linux.h

 // 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.
 
 #ifndef NET_PROXY_PROXY_CONFIG_SERVICE_LINUX_H_
 #define NET_PROXY_PROXY_CONFIG_SERVICE_LINUX_H_
 
 #include <stddef.h>
 
 #include <memory>
 #include <string>
 #include <vector>
 
 #include "base/compiler_specific.h"
 #include "base/environment.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/observer_list.h"
 #include "net/base/net_export.h"
 #include "net/proxy/proxy_config.h"
 #include "net/proxy/proxy_config_service.h"
 #include "net/proxy/proxy_server.h"
 
 namespace base {
 class SingleThreadTaskRunner;
+class SequencedTaskRunner;
 }  // namespace base
 
 namespace net {
 
 // Implementation of ProxyConfigService that retrieves the system proxy
 // settings from environment variables, gconf, gsettings, or kioslaverc (KDE).
 class NET_EXPORT_PRIVATE ProxyConfigServiceLinux : public ProxyConfigService {
  public:
   class Delegate;
 
   class SettingGetter {
    public:
     // Buffer size used in some implementations of this class when reading
     // files. Defined here so unit tests can construct worst-case inputs.
     static const size_t BUFFER_SIZE = 512;
 
     SettingGetter() {}
     virtual ~SettingGetter() {}
 
     // Initializes the class: obtains a gconf/gsettings client, or simulates
     // one, in the concrete implementations. Returns true on success. Must be
     // called before using other methods, and should be called on the thread
     // running the glib main loop.
-    // One of |glib_task_runner| and |file_task_runner| will be
-    // used for gconf/gsettings calls or reading necessary files, depending on
-    // the implementation.
-    virtual bool Init(
-        const scoped_refptr<base::SingleThreadTaskRunner>& glib_task_runner,
-        const scoped_refptr<base::SingleThreadTaskRunner>&
-            file_task_runner) = 0;
+    // Either |glib_task_runner| or an internal sequenced task runner will
+    // be used for gconf/gsettings calls or reading necessary files,
+    // depending on the implementation.

[mmenke, 2017/06/22 18:07:06]

Could we make it clearer that we're not performing file i/o on glib_task_runner?

[eroman, 2017/06/22 19:50:47]

Done. How about this:

 50     // This interface supports both GNOME and KDE implementations. In the
 51     // case of GNOME, the glib_task_runner will be used for interacting with
 52     // gconf/gsettings as those APIs have thread affinity. Whereas in the
case
 53     // of KDE, its configuration files will be monitored at well-known
locations
 54     // and glib_task_runner will not be used. Instead, blocking file I/O
 55     // operations will be posted directly using the task scheduler.

[mmenke, 2017/06/22 19:52:10]

SGTM

+    virtual bool Init(const scoped_refptr<base::SingleThreadTaskRunner>&
+                          glib_task_runner) = 0;
 
     // Releases the gconf/gsettings client, which clears cached directories and
     // stops notifications.
     virtual void ShutDown() = 0;
 
     // Requests notification of gconf/gsettings changes for proxy
     // settings. Returns true on success.
     virtual bool SetUpNotifications(Delegate* delegate) = 0;
 
     // Returns the message loop for the thread on which this object
     // handles notifications, and also on which it must be destroyed.
     // Returns NULL if it does not matter.
-    virtual const scoped_refptr<base::SingleThreadTaskRunner>&
-        GetNotificationTaskRunner() = 0;
+    virtual const scoped_refptr<base::SequencedTaskRunner>&
+    GetNotificationTaskRunner() = 0;
 
     // Returns the source of proxy settings.
     virtual ProxyConfigSource GetConfigSource() = 0;
 
     // These are all the values that can be fetched. We used to just use the
     // corresponding paths in gconf for these, but gconf is now obsolete and
     // in the future we'll be using mostly gsettings/kioslaverc so we
     // enumerate them instead to avoid unnecessary string operations.
     enum StringSetting {
       PROXY_MODE,
@@ skipping 63 matching lines @@
   // ProxyConfigServiceLinux is created on the UI thread, and
   // SetUpAndFetchInitialConfig() is immediately called to synchronously
   // fetch the original configuration and set up change notifications on
   // the UI thread.
   //
   // Past that point, it is accessed periodically through the
   // ProxyConfigService interface (GetLatestProxyConfig, AddObserver,
   // RemoveObserver) from the IO thread.
   //
   // Setting change notification callbacks can occur at any time and are
-  // run on either the UI thread (gconf/gsettings) or the file thread
-  // (KDE). The new settings are fetched on that thread, and the resulting
-  // proxy config is posted to the IO thread through
+  // run on either the UI thread (gconf/gsettings) or the sequenced task
+  // runner (KDE). The new settings are fetched on that thread, and the
+  // resulting proxy config is posted to the IO thread through
   // Delegate::SetNewProxyConfig(). We then notify observers on the IO
   // thread of the configuration change.
   //
   // ProxyConfigServiceLinux is deleted from the IO thread.
   //
   // The substance of the ProxyConfigServiceLinux implementation is
   // wrapped in the Delegate ref counted class. On deleting the
   // ProxyConfigServiceLinux, Delegate::OnDestroy() is posted to either
-  // the UI thread (gconf/gsettings) or the file thread (KDE) where change
-  // notifications will be safely stopped before releasing Delegate.
+  // the UI thread (gconf/gsettings) or a sequenced task runner (KDE)
+  // where change notifications will be safely stopped before releasing
+  // Delegate.
 
   class Delegate : public base::RefCountedThreadSafe<Delegate> {
    public:
     // Normal constructor.
     explicit Delegate(std::unique_ptr<base::Environment> env_var_getter);
 
     // Constructor for testing.
     Delegate(std::unique_ptr<base::Environment> env_var_getter,
              SettingGetter* setting_getter);
 
     // Synchronously obtains the proxy configuration. If gconf,
     // gsettings, or kioslaverc are used, also enables notifications for
     // setting changes. gconf/gsettings must only be accessed from the
     // thread running the default glib main loop, and so this method
     // must be called from the UI thread. The message loop for the IO
     // thread is specified so that notifications can post tasks to it
-    // (and for assertions). The message loop for the file thread is
-    // used to read any files needed to determine proxy settings.
+    // (and for assertions).
     void SetUpAndFetchInitialConfig(
         const scoped_refptr<base::SingleThreadTaskRunner>& glib_task_runner,
-        const scoped_refptr<base::SingleThreadTaskRunner>& io_task_runner,
-        const scoped_refptr<base::SingleThreadTaskRunner>& file_task_runner);
+        const scoped_refptr<base::SingleThreadTaskRunner>& io_task_runner);
 
     // Handler for setting change notifications: fetches a new proxy
     // configuration from settings, and if this config is different
     // than what we had before, posts a task to have it stored in
     // cached_config_.
     // Left public for simplicity.
     void OnCheckProxyConfigSettings();
 
     // Called from IO thread.
     void AddObserver(Observer* observer);
     void RemoveObserver(Observer* observer);
     ProxyConfigService::ConfigAvailability GetLatestProxyConfig(
         ProxyConfig* config);
 
-    // Posts a call to OnDestroy() to the UI or FILE thread, depending on the
-    // setting getter in use. Called from ProxyConfigServiceLinux's destructor.
+    // Posts a call to OnDestroy() to the UI or sequenced task runner,
+    // depending on the setting getter in use. Called from
+    // ProxyConfigServiceLinux's destructor.
     void PostDestroyTask();
-    // Safely stops change notifications. Posted to either the UI or FILE
-    // thread, depending on the setting getter in use.
+    // Safely stops change notifications. Posted to either the UI or
+    // sequenced task runner, depending on the setting getter in use.
     void OnDestroy();
 
    private:
     friend class base::RefCountedThreadSafe<Delegate>;
 
     ~Delegate();
 
     // Obtains an environment variable's value. Parses a proxy server
     // specification from it and puts it in result. Returns true if the
     // requested variable is defined and the value valid.
@@ skipping 63 matching lines @@
   // For testing: take alternate setting and env var getter implementations.
   explicit ProxyConfigServiceLinux(
       std::unique_ptr<base::Environment> env_var_getter);
   ProxyConfigServiceLinux(std::unique_ptr<base::Environment> env_var_getter,
                           SettingGetter* setting_getter);
 
   ~ProxyConfigServiceLinux() override;
 
   void SetupAndFetchInitialConfig(
       const scoped_refptr<base::SingleThreadTaskRunner>& glib_task_runner,
-      const scoped_refptr<base::SingleThreadTaskRunner>& io_task_runner,
-      const scoped_refptr<base::SingleThreadTaskRunner>& file_task_runner) {
-    delegate_->SetUpAndFetchInitialConfig(glib_task_runner,
-                                          io_task_runner,
-                                          file_task_runner);
+      const scoped_refptr<base::SingleThreadTaskRunner>& io_task_runner) {
+    delegate_->SetUpAndFetchInitialConfig(glib_task_runner, io_task_runner);
   }
   void OnCheckProxyConfigSettings() {
     delegate_->OnCheckProxyConfigSettings();
   }
 
   // ProxyConfigService methods:
   // Called from IO thread.
   void AddObserver(Observer* observer) override;
   void RemoveObserver(Observer* observer) override;
   ProxyConfigService::ConfigAvailability GetLatestProxyConfig(
       ProxyConfig* config) override;
 
  private:
   scoped_refptr<Delegate> delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(ProxyConfigServiceLinux);
 };
 
 }  // namespace net
 
 #endif  // NET_PROXY_PROXY_CONFIG_SERVICE_LINUX_H_