Compute digest in BackgroundThread which is limited to little cores.

Bug: 149525109
Test: atest --test-mapping apex/blobstore
Change-Id: I70333e1d880c45db15e9e1fe730f3443626aab67

apex/blobstore/service/java/com/android/server/blob/BlobStoreManagerService.java

@@ -74,6 +74,7 @@ import android.util.Xml;
 
 import com.android.internal.annotations.GuardedBy;
 import com.android.internal.annotations.VisibleForTesting;
+import com.android.internal.os.BackgroundThread;
 import com.android.internal.util.CollectionUtils;
 import com.android.internal.util.DumpUtils;
 import com.android.internal.util.FastXmlSerializer;
@@ -140,6 +141,7 @@ public class BlobStoreManagerService extends SystemService {
 
     private final Context mContext;
     private final Handler mHandler;
+    private final Handler mBackgroundHandler;
     private final Injector mInjector;
     private final SessionStateChangeListener mSessionStateChangeListener =
             new SessionStateChangeListener();
@@ -160,11 +162,12 @@ public class BlobStoreManagerService extends SystemService {
         mContext = context;
         mInjector = injector;
         mHandler = mInjector.initializeMessageHandler();
+        mBackgroundHandler = mInjector.getBackgroundHandler();
     }
 
     private static Handler initializeMessageHandler() {
         final HandlerThread handlerThread = new ServiceThread(TAG,
-                Process.THREAD_PRIORITY_BACKGROUND, true /* allowIo */);
+                Process.THREAD_PRIORITY_DEFAULT, true /* allowIo */);
         handlerThread.start();
         final Handler handler = new Handler(handlerThread.getLooper());
         Watchdog.getInstance().addThread(handler);
@@ -418,7 +421,7 @@ public class BlobStoreManagerService extends SystemService {
         public void onStateChanged(@NonNull BlobStoreSession session) {
             mHandler.post(PooledLambda.obtainRunnable(
                     BlobStoreManagerService::onStateChangedInternal,
-                    BlobStoreManagerService.this, session));
+                    BlobStoreManagerService.this, session).recycleOnUse());
         }
     }
 
@@ -437,7 +440,11 @@ public class BlobStoreManagerService extends SystemService {
                 }
                 break;
             case STATE_COMMITTED:
-                session.verifyBlobData();
+                mBackgroundHandler.post(() -> {
+                    session.computeDigest();
+                    mHandler.post(PooledLambda.obtainRunnable(
+                            BlobStoreSession::verifyBlobData, session).recycleOnUse());
+                });
                 break;
             case STATE_VERIFIED_VALID:
                 synchronized (mBlobsLock) {
@@ -1412,5 +1419,9 @@ public class BlobStoreManagerService extends SystemService {
         public Handler initializeMessageHandler() {
             return BlobStoreManagerService.initializeMessageHandler();
         }
+
+        public Handler getBackgroundHandler() {
+            return BackgroundThread.getHandler();
+        }
     }
 }

apex/blobstore/service/java/com/android/server/blob/BlobStoreSession.java

@@ -96,6 +96,10 @@ class BlobStoreSession extends IBlobStoreSession.Stub {
     @GuardedBy("mRevocableFds")
     private ArrayList<RevocableFileDescriptor> mRevocableFds = new ArrayList<>();
 
+    // This will be accessed from only one thread at any point of time, so no need to grab
+    // a lock for this.
+    private byte[] mDataDigest;
+
     @GuardedBy("mSessionLock")
     private int mState = STATE_CLOSED;
 
@@ -381,19 +385,21 @@ class BlobStoreSession extends IBlobStoreSession.Stub {
         }
     }
 
-    void verifyBlobData() {
-        byte[] actualDigest = null;
+    void computeDigest() {
         try {
             Trace.traceBegin(TRACE_TAG_SYSTEM_SERVER,
                     "computeBlobDigest-i" + mSessionId + "-l" + getSessionFile().length());
-            actualDigest = FileUtils.digest(getSessionFile(), mBlobHandle.algorithm);
+            mDataDigest = FileUtils.digest(getSessionFile(), mBlobHandle.algorithm);
         } catch (IOException | NoSuchAlgorithmException e) {
             Slog.e(TAG, "Error computing the digest", e);
         } finally {
             Trace.traceEnd(TRACE_TAG_SYSTEM_SERVER);
         }
+    }
+
+    void verifyBlobData() {
         synchronized (mSessionLock) {
-            if (actualDigest != null && Arrays.equals(actualDigest, mBlobHandle.digest)) {
+            if (mDataDigest != null && Arrays.equals(mDataDigest, mBlobHandle.digest)) {
                 mState = STATE_VERIFIED_VALID;
                 // Commit callback will be sent once the data is persisted.
             } else {

services/tests/mockingservicestests/src/com/android/server/blob/BlobStoreManagerServiceTest.java

@@ -343,5 +343,10 @@ public class BlobStoreManagerServiceTest {
         public Handler initializeMessageHandler() {
             return mHandler;
         }
+
+        @Override
+        public Handler getBackgroundHandler() {
+            return mHandler;
+        }
     }
 }