Prohibit multiple, overlapping {geolocation,battery} queries

Motivation: overlapped queries were never needed, and so prohibiting them is a lot simpler than allowing them.

Review URL: https://codereview.chromium.org/897213006

Cr-Commit-Position: refs/heads/master@{#320598}

4 files changed, 28 insertions, 20 deletions

diff --git a/device/battery/android/java/src/org/chromium/device/battery/BatteryMonitorImpl.java b/device/battery/android/java/src/org/chromium/device/battery/BatteryMonitorImpl.java
index 364e21a..dd0ee5e 100644
--- a/device/battery/android/java/src/org/chromium/device/battery/BatteryMonitorImpl.java
+++ b/device/battery/android/java/src/org/chromium/device/battery/BatteryMonitorImpl.java
@@ -4,28 +4,29 @@
 
 package org.chromium.device.battery;
 
+import android.util.Log;
+
 import org.chromium.mojo.system.MojoException;
 import org.chromium.mojom.device.BatteryMonitor;
 import org.chromium.mojom.device.BatteryStatus;
 
-import java.util.ArrayList;
-import java.util.List;
-
 /**
  * Android implementation of the battery monitor service defined in
  * device/battery/battery_monitor.mojom.
  */
 public class BatteryMonitorImpl implements BatteryMonitor {
+
+    private static final String TAG = "BatteryMonitorImpl";
+
     // Factory that created this instance and notifies it about battery status changes.
     private final BatteryMonitorFactory mFactory;
-    private final List<QueryNextStatusResponse> mCallbacks;
+    private QueryNextStatusResponse mCallback;
     private BatteryStatus mStatus;
     private boolean mHasStatusToReport;
     private boolean mSubscribed;
 
     public BatteryMonitorImpl(BatteryMonitorFactory batteryMonitorFactory) {
         mFactory = batteryMonitorFactory;
-        mCallbacks = new ArrayList<QueryNextStatusResponse>();
         mHasStatusToReport = false;
         mSubscribed = true;
     }
@@ -49,7 +50,13 @@ public class BatteryMonitorImpl implements BatteryMonitor {
 
     @Override
     public void queryNextStatus(QueryNextStatusResponse callback) {
-        mCallbacks.add(callback);
+        if (mCallback != null) {
+            Log.e(TAG, "Overlapped call to queryNextStatus!");
+            unsubscribe();
+            return;
+        }
+
+        mCallback = callback;
 
         if (mHasStatusToReport) {
             reportStatus();
@@ -60,16 +67,14 @@ public class BatteryMonitorImpl implements BatteryMonitor {
         mStatus = batteryStatus;
         mHasStatusToReport = true;
 
-        if (!mCallbacks.isEmpty()) {
+        if (mCallback != null) {
             reportStatus();
         }
     }
 
     void reportStatus() {
-        for (QueryNextStatusResponse callback : mCallbacks) {
-            callback.call(mStatus);
-        }
-        mCallbacks.clear();
+        mCallback.call(mStatus);
+        mCallback = null;
         mHasStatusToReport = false;
     }
 }
diff --git a/device/battery/battery_monitor.mojom b/device/battery/battery_monitor.mojom
index 88a43d2..1db7868 100644
--- a/device/battery/battery_monitor.mojom
+++ b/device/battery/battery_monitor.mojom
@@ -10,6 +10,6 @@ interface BatteryMonitor {
   // Battery status is reported once it changes or immediately if this is the
   // first call to QueryNextStatus on this instance. QueryNextStatus calls may
   // be throttled by the service. Overlapping calls to QueryNextStatus are
-  // supported.
+  // prohibited and will be treated as a connection error.
   QueryNextStatus() => (BatteryStatus status);
 };
diff --git a/device/battery/battery_monitor_impl.cc b/device/battery/battery_monitor_impl.cc
index 62cbf60..b538394 100644
--- a/device/battery/battery_monitor_impl.cc
+++ b/device/battery/battery_monitor_impl.cc
@@ -5,6 +5,7 @@
 #include "device/battery/battery_monitor_impl.h"
 
 #include "base/bind.h"
+#include "base/logging.h"
 
 namespace device {
 
@@ -29,7 +30,12 @@ BatteryMonitorImpl::~BatteryMonitorImpl() {
 
 void BatteryMonitorImpl::QueryNextStatus(
     const BatteryStatusCallback& callback) {
-  callbacks_.push_back(callback);
+  if (!callback_.is_null()) {
+    DVLOG(1) << "Overlapped call to QueryNextStatus!";
+    delete this;
+    return;
+  }
+  callback_ = callback;
 
   if (status_to_report_)
     ReportStatus();
@@ -42,14 +48,13 @@ void BatteryMonitorImpl::DidChange(const BatteryStatus& battery_status) {
   status_ = battery_status;
   status_to_report_ = true;
 
-  if (!callbacks_.empty())
+  if (!callback_.is_null())
     ReportStatus();
 }
 
 void BatteryMonitorImpl::ReportStatus() {
-  for (const auto& callback : callbacks_)
-    callback.Run(status_.Clone());
-  callbacks_.clear();
+  callback_.Run(status_.Clone());
+  callback_.reset();
 
   status_to_report_ = false;
 }
diff --git a/device/battery/battery_monitor_impl.h b/device/battery/battery_monitor_impl.h
index 7fb1c139..6bf65f7 100644
--- a/device/battery/battery_monitor_impl.h
+++ b/device/battery/battery_monitor_impl.h
@@ -5,8 +5,6 @@
 #ifndef DEVICE_BATTERY_BATTERY_MONITOR_IMPL_H_
 #define DEVICE_BATTERY_BATTERY_MONITOR_IMPL_H_
 
-#include <vector>
-
 #include "base/memory/scoped_ptr.h"
 #include "device/battery/battery_export.h"
 #include "device/battery/battery_monitor.mojom.h"
@@ -35,7 +33,7 @@ class BatteryMonitorImpl : public BatteryMonitor {
 
   mojo::StrongBinding<BatteryMonitor> binding_;
   scoped_ptr<BatteryStatusService::BatteryUpdateSubscription> subscription_;
-  std::vector<BatteryStatusCallback> callbacks_;
+  BatteryStatusCallback callback_;
   BatteryStatus status_;
   bool status_to_report_;