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Start and stop BLE scans from a background thread to prevent blocking the UI (issue #136) #430

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merged 1 commit into from
Oct 20, 2016
Merged

Start and stop BLE scans from a background thread to prevent blocking the UI (issue #136) #430

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1 change: 1 addition & 0 deletions src/main/java/org/altbeacon/beacon/service/BeaconService.java
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Expand Up @@ -273,6 +273,7 @@ public void onDestroy() {
LogManager.i(TAG, "onDestroy called. stopping scanning");
handler.removeCallbacksAndMessages(null);
mCycledScanner.stop();
mCycledScanner.destroy();
monitoringStatus.stopStatusPreservation();
}

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15 changes: 14 additions & 1 deletion src/main/java/org/altbeacon/beacon/service/scanner/CycledLeScanner.java
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Expand Up @@ -12,6 +12,8 @@
import android.content.pm.PackageManager;
import android.os.Build;
import android.os.Handler;
import android.os.HandlerThread;
import android.os.Looper;
import android.os.SystemClock;

import org.altbeacon.beacon.BeaconManager;
Expand Down Expand Up @@ -40,7 +42,10 @@ public abstract class CycledLeScanner {
private long mScanPeriod;

protected long mBetweenScanPeriod;
protected final Handler mHandler = new Handler();

protected final Handler mHandler = new Handler(Looper.getMainLooper());
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What is the point of calling Looper.getMainLooper() here? This handler will never need to communicate with the main UI thread, so why not let it have its own looper?

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The default, parameterless Handler constructor uses the Looper from the current thread (as documented here and here).

In this particular case, CycledLeScanner is always instantiated from the main thread (from BeaconService.onCreate()) and consequently, that Handler will already use the main thread's looper.
This addition doesn't modify the current logic, it's only a futureproof guarantee that the class behaviour won't change if in the future if CycledLeScanner is instantiated from another thread that doesn't have a Looper (you would immediately notice because the Handler creation would crash).

protected final Handler mScanHandler;
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Is there a reason to use a HandlerThread here? Why not just construct mScanHandler = new Handler();? Then you don't need to clean up the handler thread later.

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@davidgyoung see my answer below (and this doc), this is the change that makes the whole PR work: by creating it with new Handler() you'd be using the Looper from the thread that's instantiating CycledLeScanner, which is the main thread.

Instead, by creating a HandlerThread (which is just a thread with a Looper attached to it) we make sure the "expensive" Bluetooth code from the SDK is posted and executed in our own worker thread.

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OK, got it now... apologies, it's been awhile, it's been awhile since I looked at this code. I was incorrectly thinking that new Handler() always creates a new thread.

private final HandlerThread mScanThread;

protected final BluetoothCrashResolver mBluetoothCrashResolver;
protected final CycledLeScanCallback mCycledLeScanCallback;
Expand All @@ -57,6 +62,10 @@ protected CycledLeScanner(Context context, long scanPeriod, long betweenScanPeri
mCycledLeScanCallback = cycledLeScanCallback;
mBluetoothCrashResolver = crashResolver;
mBackgroundFlag = backgroundFlag;

mScanThread = new HandlerThread("CycledLeScannerThread");
mScanThread.start();
mScanHandler = new Handler(mScanThread.getLooper());
}

public static CycledLeScanner createScanner(Context context, long scanPeriod, long betweenScanPeriod, boolean backgroundFlag, CycledLeScanCallback cycledLeScanCallback, BluetoothCrashResolver crashResolver) {
Expand Down Expand Up @@ -156,6 +165,10 @@ public void stop() {
}
}

public void destroy() {
mScanThread.quit();
}

protected abstract void stopScan();

protected abstract boolean deferScanIfNeeded();
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56 changes: 43 additions & 13 deletions src/main/java/org/altbeacon/beacon/service/scanner/CycledLeScannerForJellyBeanMr2.java
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Expand Up @@ -18,17 +18,9 @@ public CycledLeScannerForJellyBeanMr2(Context context, long scanPeriod, long bet
super(context, scanPeriod, betweenScanPeriod, backgroundFlag, cycledLeScanCallback, crashResolver);
}

@SuppressWarnings("deprecation")
@Override
protected void stopScan() {
try {
BluetoothAdapter bluetoothAdapter = getBluetoothAdapter();
if (bluetoothAdapter != null) {
bluetoothAdapter.stopLeScan(getLeScanCallback());
}
} catch (Exception e) {
LogManager.e(e, TAG, "Internal Android exception scanning for beacons");
}
postStopLeScan();
}

@Override
Expand All @@ -54,19 +46,57 @@ public void run() {
return false;
}

@SuppressWarnings("deprecation")
@Override
protected void startScan() {
getBluetoothAdapter().startLeScan(getLeScanCallback());
postStartLeScan();
}

@SuppressWarnings("deprecation")
@Override
protected void finishScan() {
getBluetoothAdapter().stopLeScan(getLeScanCallback());
postStopLeScan();
mScanningPaused = true;
}

private void postStartLeScan() {
final BluetoothAdapter bluetoothAdapter = getBluetoothAdapter();
if (bluetoothAdapter == null) {
return;
}
final BluetoothAdapter.LeScanCallback leScanCallback = getLeScanCallback();
mScanHandler.removeCallbacksAndMessages(null);
mScanHandler.post(new Runnable() {
@Override
public void run() {
try {
//noinspection deprecation
bluetoothAdapter.startLeScan(leScanCallback);
} catch (Exception e) {
LogManager.e(e, TAG, "Internal Android exception in startLeScan()");
}
}
});
}

private void postStopLeScan() {
final BluetoothAdapter bluetoothAdapter = getBluetoothAdapter();
if (bluetoothAdapter == null) {
return;
}
final BluetoothAdapter.LeScanCallback leScanCallback = getLeScanCallback();
mScanHandler.removeCallbacksAndMessages(null);
mScanHandler.post(new Runnable() {
@Override
public void run() {
try {
//noinspection deprecation
bluetoothAdapter.stopLeScan(leScanCallback);
} catch (Exception e) {
LogManager.e(e, TAG, "Internal Android exception in stopLeScan()");
}
}
});
}

private BluetoothAdapter.LeScanCallback getLeScanCallback() {
if (leScanCallback == null) {
leScanCallback =
Expand Down
76 changes: 46 additions & 30 deletions src/main/java/org/altbeacon/beacon/service/scanner/CycledLeScannerForLollipop.java
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Expand Up @@ -8,7 +8,6 @@
import android.bluetooth.le.ScanResult;
import android.bluetooth.le.ScanSettings;
import android.content.Context;
import android.os.Build;
import android.os.ParcelUuid;
import android.os.SystemClock;

Expand Down Expand Up @@ -39,20 +38,7 @@ public CycledLeScannerForLollipop(Context context, long scanPeriod, long between

@Override
protected void stopScan() {
try {
if (getScanner() != null) {
try {
getScanner().stopScan((android.bluetooth.le.ScanCallback) getNewLeScanCallback());
}
catch (NullPointerException npe) {
// Necessary because of https://code.google.com/p/android/issues/detail?id=160503
LogManager.e(TAG, "Cannot stop scan. Unexpected NPE.", npe);
}
}
}
catch (IllegalStateException e) {
LogManager.w(TAG, "Cannot stop scan. Bluetooth may be turned off.");
}
postStopLeScan();
}

/*
Expand Down Expand Up @@ -181,21 +167,7 @@ protected void startScan() {
settings = (new ScanSettings.Builder().setScanMode(ScanSettings.SCAN_MODE_LOW_LATENCY)).build();
}

try {
if (getScanner() != null) {
ScanCallback callback = getNewLeScanCallback();
try {
getScanner().startScan(filters, settings, callback);
}
catch (NullPointerException npe) {
// Necessary because of https://code.google.com/p/android/issues/detail?id=160503
LogManager.w(TAG, "Cannot start scan. Unexpected NPE.", npe);
}
}
}
catch (IllegalStateException e) {
LogManager.w(TAG, "Cannot start scan. Bluetooth may be turned off.");
}
postStartLeScan(filters, settings);
}

@Override
Expand All @@ -205,6 +177,50 @@ protected void finishScan() {
mScanningPaused = true;
}

private void postStartLeScan(final List<ScanFilter> filters, final ScanSettings settings) {
final BluetoothLeScanner scanner = getScanner();
if (scanner == null) {
return;
}
final ScanCallback scanCallback = getNewLeScanCallback();
mScanHandler.removeCallbacksAndMessages(null);
mScanHandler.post(new Runnable() {
@Override
public void run() {
try {
scanner.startScan(filters, settings, scanCallback);
} catch (IllegalStateException e) {
LogManager.w(TAG, "Cannot start scan. Bluetooth may be turned off.");
} catch (NullPointerException npe) {
// Necessary because of https://code.google.com/p/android/issues/detail?id=160503
LogManager.e(TAG, "Cannot start scan. Unexpected NPE.", npe);
}
}
});
}

private void postStopLeScan() {
final BluetoothLeScanner scanner = getScanner();
if (scanner == null) {
return;
}
final ScanCallback scanCallback = getNewLeScanCallback();
mScanHandler.removeCallbacksAndMessages(null);
mScanHandler.post(new Runnable() {
@Override
public void run() {
try {
scanner.stopScan(scanCallback);
} catch (IllegalStateException e) {
LogManager.w(TAG, "Cannot stop scan. Bluetooth may be turned off.");
} catch (NullPointerException npe) {
// Necessary because of https://code.google.com/p/android/issues/detail?id=160503
LogManager.e(TAG, "Cannot stop scan. Unexpected NPE.", npe);
}
}
});
}

private BluetoothLeScanner getScanner() {
if (mScanner == null) {
LogManager.d(TAG, "Making new Android L scanner");
Expand Down