Add content API for requesting the current geolocation

content/browser/geolocation/geolocation_provider.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 CONTENT_BROWSER_GEOLOCATION_GEOLOCATION_PROVIDER_H_
 #define CONTENT_BROWSER_GEOLOCATION_GEOLOCATION_PROVIDER_H_
 #pragma once
 
 #include <map>
+#include <vector>
 
+#include "base/basictypes.h"
+#include "base/compiler_specific.h"
 #include "base/threading/thread.h"
 #include "content/browser/geolocation/geolocation_observer.h"
 #include "content/common/content_export.h"
+#include "content/public/browser/geolocation.h"
 #include "content/public/common/geoposition.h"
 
 class GeolocationArbitrator;
+class GeolocationProviderTest;
+template<typename Type> struct DefaultSingletonTraits;
 
-template<typename Type>
-struct DefaultSingletonTraits;
-
-// This is the main API to the geolocation subsystem. The application
-// will hold a single instance of this class, and can register multiple
-// observers which will be notified of location updates. Underlying location
-// arbitrator will only be enabled whilst there is at least one observer
-// registered.
+// This is the main API to the geolocation subsystem. The application will hold
+// a single instance of this class and can register multiple clients to be
+// notified of location changes:
+// * Observers are registered by AddObserver() and will keep receiving updates
+//   until unregistered by RemoveObserver().
+// * Callbacks are registered by RequestCallback() and will be called exactly
+//   once when the next update becomes available.
+// The application must instantiate the GeolocationProvider on the IO thread and
+// must communicate with it on the same thread.
+// The underlying location arbitrator will only be enabled whilst there is at
+// least one registered observer or pending callback. The arbitrator and the
+// location providers it uses run on a separate Geolocation thread.
 class CONTENT_EXPORT GeolocationProvider
     : public base::Thread, public GeolocationObserver {
  public:
-  GeolocationProvider();
-
-  // Must be called from the same thread as the GeolocationProvider was created
-  // on. The GeolocationObserverOptions passed are used as a 'hint' for the
-  // provider preferences for this particular observer, however the observer
-  // could receive callbacks for best available locations from any active
-  // provider whilst it is registered.
-  // If an existing observer is added a second time it's options are updated
+  // The GeolocationObserverOptions passed are used as a 'hint' for the provider
+  // preferences for this particular observer, however the observer could
+  // receive updates for best available locations from any active provider
+  // whilst it is registered.
+  // If an existing observer is added a second time, its options are updated
   // but only a single call to RemoveObserver() is required to remove it.
   void AddObserver(GeolocationObserver* delegate,
                    const GeolocationObserverOptions& update_options);
 
   // Remove a previously registered observer. No-op if not previously registered
   // via AddObserver(). Returns true if the observer was removed.
   bool RemoveObserver(GeolocationObserver* delegate);
 
+  // Request a single callback when the next location update becomes available.
+  // Callbacks must only be requested by code that is allowed to access the
+  // location. No further permission checks will be made.
+  void RequestCallback(const content::GeolocationUpdateCallback& callback);
+
   void OnPermissionGranted();
   bool HasPermissionBeenGranted() const;
 
-  // GeolocationObserver
+  // GeolocationObserver implementation.
   virtual void OnLocationUpdate(const content::Geoposition& position) OVERRIDE;
 
-  // Overrides the location for automation/testing. Updates any current
-  // observers with the overriden position. Any further updates from location
-  // providers will be ignored.
+  // Overrides the location for automation/testing. Suppresses any further
+  // updates from the actual providers and sends an update with the overridden
+  // position to all registered clients.
   void OverrideLocationForTesting(
       const content::Geoposition& override_position);
 
   // Gets a pointer to the singleton instance of the location relayer, which
-  // is in turn bound to the browser's global context objects. Ownership is NOT
-  // returned.
+  // is in turn bound to the browser's global context objects. This must only be
+  // called on the IO thread so that the GeolocationProvider is always
+  // instantiated on the same thread. Ownership is NOT returned.
   static GeolocationProvider* GetInstance();
 
+ protected:
+  friend struct DefaultSingletonTraits<GeolocationProvider>;
+  GeolocationProvider();
+  virtual ~GeolocationProvider();
+
+ private:
   typedef std::map<GeolocationObserver*, GeolocationObserverOptions>
       ObserverMap;
 
- private:
-  friend struct DefaultSingletonTraits<GeolocationProvider>;
-  virtual ~GeolocationProvider();
+  typedef std::vector<content::GeolocationUpdateCallback> CallbackList;
 
-  bool OnClientThread() const;
   bool OnGeolocationThread() const;
 
-  // When the observer list changes, we may start the thread and the required
-  // providers, or stop them.
-  void OnObserversChanged();
+  // Start and stop providers as needed when clients are added or removed.
+  void OnClientsChanged();
 
-  // Stop the providers when there are no more observers. Note that once our
-  // thread is started, we'll keep it alive (but with no pending messages).
+  // Stops the providers when there are no more registered clients. Note that
+  // once the Geolocation thread is started, it will stay alive (but sitting
+  // idle without any pending messages).
   void StopProviders();
 
-  // Starts or updates the observers' geolocation options
-  // (delegates to arbitrator).
+  // Starts the geolocation providers or updates their options (delegates to
+  // arbitrator).
   void StartProviders(const GeolocationObserverOptions& options);
 
-  // Update the providers on the geolocation thread, which must be running.
+  // Updates the providers on the geolocation thread, which must be running.
   void InformProvidersPermissionGranted();
 
-  // Notifies observers when a new position fix is available.
-  void NotifyObservers(const content::Geoposition& position);
+  // Notifies all registered clients that a position update is available.
+  void NotifyClients(const content::Geoposition& position);
 
   // Thread
   virtual void Init() OVERRIDE;
   virtual void CleanUp() OVERRIDE;
 
-  scoped_refptr<base::MessageLoopProxy> client_loop_;
-
-  // Only used on client thread
+  // Only used on the IO thread
   ObserverMap observers_;
+  CallbackList callbacks_;
   bool is_permission_granted_;
   content::Geoposition position_;
+
   // True only in testing, where we want to use a custom position.
   bool ignore_location_updates_;
 
   // Only to be used on the geolocation thread.
   GeolocationArbitrator* arbitrator_;
 
   DISALLOW_COPY_AND_ASSIGN(GeolocationProvider);
 };
 
 #endif  // CONTENT_BROWSER_GEOLOCATION_GEOLOCATION_PROVIDER_H_