Use Android callback API to obtain cellular signal strength

net/android/java/src/org/chromium/net/AndroidCellularSignalStrength.java

 // Copyright 2016 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.
 
 package org.chromium.net;
 
-import android.Manifest;
 import android.annotation.TargetApi;
 import android.content.Context;
-import android.content.pm.PackageManager;
 import android.os.Build;
-import android.os.Process;
-import android.telephony.CellInfo;
-import android.telephony.CellInfoCdma;
-import android.telephony.CellInfoGsm;
-import android.telephony.CellInfoLte;
-import android.telephony.CellInfoWcdma;
+import android.os.Handler;
+import android.os.HandlerThread;
+import android.telephony.PhoneStateListener;
+import android.telephony.SignalStrength;
 import android.telephony.TelephonyManager;
 
+import org.chromium.base.ApplicationState;
+import org.chromium.base.ApplicationStatus;
 import org.chromium.base.ContextUtils;
+import org.chromium.base.ThreadUtils;
 import org.chromium.base.annotations.CalledByNative;
 import org.chromium.base.annotations.JNINamespace;
-
-import java.util.Iterator;
-import java.util.List;
+import org.chromium.base.annotations.SuppressFBWarnings;
 
 /**
- * This class interacts with the CellInfo API provided by Android. This class is thread safe.
+ * This class provides the cellular signal strength using the APIs provided by Android. This class
+ * is thread safe.
  */
-@JNINamespace("net::android::cellular_signal_strength")
+@JNINamespace("net::android")
 public class AndroidCellularSignalStrength {
+    // {@link mSignalLevel} is set to volatile since may be accessed across threads.
+    private volatile int mSignalLevel = CellularSignalStrengthError.ERROR_NOT_SUPPORTED;
+
+    @SuppressFBWarnings("URF_UNREAD_FIELD")
+    private CellStateListener mCellStateListener;

[pauljensen, 2017/06/23 14:31:25]

unused, remove

[tbansal1, 2017/06/26 16:08:00]

umm, this is in use.

[pauljensen, 2017/06/26 16:24:22]

Where is the use?

[tbansal1, 2017/06/26 16:28:09]

mCellStateListener is used in Line 100 below in the ctor of
AndroidCellularSignalStrength.

[pauljensen, 2017/06/26 16:29:37]

There is a dead write, but no use of it.

[tbansal1, 2017/06/26 16:49:28]

Thanks. Fixed.

+
+    private static final AndroidCellularSignalStrength sInstance =
+            new AndroidCellularSignalStrength();

[pauljensen, 2017/06/23 14:31:25]

When is this created?  I think statics are initialized when the class is first
referenced.  Is this during JNI registration?  if so we may not want to always
do this so early, e.g. if getSignalStrengthLevel() is never called.  Perhaps we
should make this non-final and have a synchronized block in
getSignalStrengthLevel() that initializes sInstance if it's not yet initialized.

[tbansal1, 2017/06/26 16:08:00]

This is created when the static object is first referenced. That happens when
the signal strength is first queried from the native. If the signal strength is
never queried, the object is not created. I verified using Log statements. Also,
this matches with  https://stackoverflow.com/a/3499322.

+
     /**
-     * @return Signal strength (in dbM) for the currently registered cellular network. Returns
-     * {@link CellularSignalStrengthError#ERROR_NOT_SUPPORTED} if the signal strength is
-     * unavailable or if there are multiple cellular radios on the device.
+     * This class listens to the changes in the cellular signal strength level and updates {@link
+     * mSignalLevel}. {@link CellStateListener} registers as a signal strength observer only if the
+     * application has running activities.
      */
-    @TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR2)
-    @CalledByNative
-    public static int getSignalStrengthDbm() {
-        List<CellInfo> cellInfos = getRegisteredCellInfo();
-        return cellInfos == null || cellInfos.size() != 1
-                ? CellularSignalStrengthError.ERROR_NOT_SUPPORTED
-                : getSignalStrengthDbm(cellInfos.get(0));
+    private class CellStateListener
+            extends PhoneStateListener implements ApplicationStatus.ApplicationStateListener {
+        private final TelephonyManager mTelephonyManager;
+
+        CellStateListener() {
+            ThreadUtils.assertOnBackgroundThread();
+
+            mTelephonyManager =
+                    (TelephonyManager) ContextUtils.getApplicationContext().getSystemService(
+                            Context.TELEPHONY_SERVICE);
+
+            if (mTelephonyManager.getSimState() != TelephonyManager.SIM_STATE_READY) return;
+
+            ApplicationStatus.registerApplicationStateListener(this);
+            onApplicationStateChange(ApplicationStatus.getStateForApplication());
+        }
+
+        private void register() {
+            mTelephonyManager.listen(this, PhoneStateListener.LISTEN_SIGNAL_STRENGTHS);
+        }
+
+        private void unregister() {
+            mSignalLevel = CellularSignalStrengthError.ERROR_NOT_SUPPORTED;

[pauljensen, 2017/06/23 14:31:25]

This is racy.  An onSignalStrengthsChanged() event could already be queued up in
the Looper and could fire after unregister() sets mSignalLevel.  You may want to
add a "private boolean mRegistered" and check it in onSignalStrengthsChanged()

[tbansal1, 2017/06/26 16:08:00]

Done.

+            mTelephonyManager.listen(this, PhoneStateListener.LISTEN_NONE);
+        }
+
+        @Override
+        @TargetApi(Build.VERSION_CODES.M)
+        public void onSignalStrengthsChanged(SignalStrength signalStrength) {
+            mSignalLevel = signalStrength.getLevel();
+        }
+
+        // ApplicationStatus.ApplicationStateListener
+        @Override
+        public void onApplicationStateChange(int newState) {
+            if (newState == ApplicationState.HAS_RUNNING_ACTIVITIES) {
+                register();
+            } else if (newState == ApplicationState.HAS_PAUSED_ACTIVITIES) {
+                unregister();
+            }
+        }
+    }
+
+    private AndroidCellularSignalStrength() {
+        if (!isAPIAvailable(ContextUtils.getApplicationContext())) return;
+
+        HandlerThread handlerThread = new HandlerThread("AndroidCellularSignalStrength");
+        handlerThread.start();
+
+        new Handler(handlerThread.getLooper()).post(new Runnable() {
+            @Override
+            public void run() {
+                mCellStateListener = new CellStateListener();
+            }
+        });
     }
 
     /**
      * @return the signal strength level (between 0 and 4, both inclusive) for the currently
      * registered cellular network with lower value indicating lower signal strength. Returns
      * {@link CellularSignalStrengthError#ERROR_NOT_SUPPORTED} if the signal strength level is
-     * unavailable or if there are multiple cellular radios on the device.
+     * unavailable.
      */
-    @TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR2)
+    @TargetApi(Build.VERSION_CODES.M)
     @CalledByNative
-    public static int getSignalStrengthLevel() {
-        List<CellInfo> cellInfos = getRegisteredCellInfo();
-        return cellInfos == null || cellInfos.size() != 1
-                ? CellularSignalStrengthError.ERROR_NOT_SUPPORTED
-                : getSignalStrengthLevel(cellInfos.get(0));
+    private static int getSignalStrengthLevel() {
+        return sInstance.mSignalLevel;
     }
 
     /**
      * Returns true if the API for quering the signal strength is available.
-     * {@link android.telephony#CellInfoWcdma} is only available on API Level
-     * {@link Build.VERSION_CODES#JELLY_BEAN_MR2} and higher. Also verifies that appropriate
-     * permissions are already available. This ensures that on Android M and higher, Chromium will
-     * not request run-time permission from the user when querying for cellular signal strength.
-     * TODO(tbansal): Consider using {@link TelephonyManager#getNeighboringCellInfo}
-     * for earlier versions of Android.
-    */
-    private static boolean isAPIAvailable() {
-        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN_MR2) return false;
-
-        try {
-            return ContextUtils.getApplicationContext().checkPermission(
-                           Manifest.permission.ACCESS_COARSE_LOCATION, Process.myPid(),
-                           Process.myUid())
-                    == PackageManager.PERMISSION_GRANTED;
-        } catch (Exception ignored) {
-            // Work around certain platforms where this method sometimes throws a runtime exception.
-            // See crbug.com/663360.
-        }
-        return false;
-    }
-
-    /**
-     * Returns all observed cell information from all radios on the device including the primary
-     * and neighboring cells. Returns only the information of cells that are registered to a
-     * mobile network. May return {@code null}.
+     * {@link android.telephony.SignalStrength#getLevel} is only available on API Level
+     * {@link Build.VERSION_CODES#M} and higher.
      */
-    @TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR2)
-    private static List<CellInfo> getRegisteredCellInfo() {
-        if (!isAPIAvailable()) {
-            return null;
-        }
-
-        TelephonyManager telephonyManager =
-                (TelephonyManager) ContextUtils.getApplicationContext().getSystemService(
-                        Context.TELEPHONY_SERVICE);
-        if (telephonyManager == null) {
-            return null;
-        }
-
-        List<CellInfo> cellInfos = telephonyManager.getAllCellInfo();
-        if (cellInfos == null) {
-            return null;
-        }
-
-        Iterator<CellInfo> iter = cellInfos.iterator();
-        while (iter.hasNext()) {
-            if (!iter.next().isRegistered()) {
-                iter.remove();
-            }
-        }
-        return cellInfos;
-    }
-
-    /**
-     * @return Signal strength (in dbM) from {@link cellInfo}. Returns {@link
-     * CellularSignalStrengthError#ERROR_NOT_SUPPORTED} if the signal strength is unavailable.
-     */
-    @TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR2)
-    private static int getSignalStrengthDbm(CellInfo cellInfo) {
-        if (cellInfo instanceof CellInfoCdma) {
-            return ((CellInfoCdma) cellInfo).getCellSignalStrength().getDbm();
-        }
-        if (cellInfo instanceof CellInfoGsm) {
-            return ((CellInfoGsm) cellInfo).getCellSignalStrength().getDbm();
-        }
-        if (cellInfo instanceof CellInfoLte) {
-            return ((CellInfoLte) cellInfo).getCellSignalStrength().getDbm();
-        }
-        if (cellInfo instanceof CellInfoWcdma) {
-            return ((CellInfoWcdma) cellInfo).getCellSignalStrength().getDbm();
-        }
-        return CellularSignalStrengthError.ERROR_NOT_SUPPORTED;
-    }
-
-    /**
-     * @return the signal level from {@link cellInfo}. Returns {@link
-     * CellularSignalStrengthError#ERROR_NOT_SUPPORTED} if the signal
-     * level is unavailable with lower value indicating lower signal strength.
-     */
-    @TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR2)
-    private static int getSignalStrengthLevel(CellInfo cellInfo) {
-        if (cellInfo instanceof CellInfoCdma) {
-            return ((CellInfoCdma) cellInfo).getCellSignalStrength().getLevel();
-        }
-        if (cellInfo instanceof CellInfoGsm) {
-            return ((CellInfoGsm) cellInfo).getCellSignalStrength().getLevel();
-        }
-        if (cellInfo instanceof CellInfoLte) {
-            return ((CellInfoLte) cellInfo).getCellSignalStrength().getLevel();
-        }
-        if (cellInfo instanceof CellInfoWcdma) {
-            return ((CellInfoWcdma) cellInfo).getCellSignalStrength().getLevel();
-        }
-        return CellularSignalStrengthError.ERROR_NOT_SUPPORTED;
+    private static boolean isAPIAvailable(Context context) {
+        return Build.VERSION.SDK_INT >= Build.VERSION_CODES.M;
     }
 }