Fix RootScanner to execute scan at least once before cancelling it.

Previously RootScanner is implemented by FutureTask, and if it is
cancelled before it starts running in background thread, the scan will
be never executed.

The CL stops using FutureTask and introduces CountDownLatch to control
UpdateRootsRunnable.

BUG=27369585

Change-Id: Ica8799faba0a8e5ca91a6b8be36dc4f5118d6333

diff --git a/packages/MtpDocumentsProvider/src/com/android/mtp/MtpDocumentsProvider.java b/packages/MtpDocumentsProvider/src/com/android/mtp/MtpDocumentsProvider.java
index 4849978..15a74e4 100644 (file)
--- a/packages/MtpDocumentsProvider/src/com/android/mtp/MtpDocumentsProvider.java
+++ b/packages/MtpDocumentsProvider/src/com/android/mtp/MtpDocumentsProvider.java
@@ -394,6 +394,7 @@ public class MtpDocumentsProvider extends DocumentsProvider {
                 for (final int id : mMtpManager.getOpenedDeviceIds()) {
                     closeDeviceInternal(id);
                 }
+                mRootScanner.pause();
             } catch (InterruptedException|IOException e) {
                 // It should fail unit tests by throwing runtime exception.
                 throw new RuntimeException(e);

diff --git a/packages/MtpDocumentsProvider/src/com/android/mtp/RootScanner.java b/packages/MtpDocumentsProvider/src/com/android/mtp/RootScanner.java
index a48bf12..76f53c4 100644 (file)
--- a/packages/MtpDocumentsProvider/src/com/android/mtp/RootScanner.java
+++ b/packages/MtpDocumentsProvider/src/com/android/mtp/RootScanner.java
@@ -26,7 +26,6 @@ import java.io.FileNotFoundException;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
-import java.util.concurrent.FutureTask;
 import java.util.concurrent.TimeUnit;
 
 final class RootScanner {
@@ -56,7 +55,7 @@ final class RootScanner {
     final MtpDatabase mDatabase;
 
     ExecutorService mExecutor;
-    FutureTask<Void> mCurrentTask;
+    private UpdateRootsRunnable mCurrentTask;
 
     RootScanner(
             ContentResolver resolver,
@@ -84,13 +83,12 @@ final class RootScanner {
             mExecutor = Executors.newSingleThreadExecutor();
         }
         if (mCurrentTask != null) {
-            // Cancel previous task.
-            mCurrentTask.cancel(true);
+            // Stop previous task.
+            mCurrentTask.stop();
         }
-        final UpdateRootsRunnable runnable = new UpdateRootsRunnable();
-        mCurrentTask = new FutureTask<Void>(runnable, null);
-        mExecutor.submit(mCurrentTask);
-        return runnable.mFirstScanCompleted;
+        mCurrentTask = new UpdateRootsRunnable();
+        mExecutor.execute(mCurrentTask);
+        return mCurrentTask.mFirstScanCompleted;
     }
 
     /**
@@ -112,13 +110,21 @@ final class RootScanner {
      * Runnable to scan roots and update the database information.
      */
     private final class UpdateRootsRunnable implements Runnable {
+        /**
+         * Count down latch that specifies the runnable is stopped.
+         */
+        final CountDownLatch mStopped = new CountDownLatch(1);
+
+        /**
+         * Count down latch that specifies the first scan is completed.
+         */
         final CountDownLatch mFirstScanCompleted = new CountDownLatch(1);
 
         @Override
         public void run() {
             Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
             int pollingCount = 0;
-            while (true) {
+            while (mStopped.getCount() > 0) {
                 boolean changed = false;
 
                 // Update devices.
@@ -170,12 +176,16 @@ final class RootScanner {
                     // Use SHORT_POLLING_PERIOD for the first SHORT_POLLING_TIMES because it is
                     // more likely to add new root just after the device is added.
                     // TODO: Use short interval only for a device that is just added.
-                    Thread.sleep(pollingCount > SHORT_POLLING_TIMES ?
-                        LONG_POLLING_INTERVAL : SHORT_POLLING_INTERVAL);
+                    mStopped.await(pollingCount > SHORT_POLLING_TIMES ?
+                            LONG_POLLING_INTERVAL : SHORT_POLLING_INTERVAL, TimeUnit.MILLISECONDS);
                 } catch (InterruptedException exp) {
                     break;
                 }
             }
         }
+
+        void stop() {
+            mStopped.countDown();
+        }
     }
 }