fixed a leak when cross process locking didn't close a file

An intermediate RandomAccessFile created while acquiring the lock
was not closed.

Also pulled the cross process locking logic out into a separate class.

Author: fredquintana

firebase-installations/src/main/java/com/google/firebase/installations/CrossProcessLock.java

@@ -0,0 +1,56 @@
+// Copyright 2019 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.firebase.installations;
+
+import android.content.Context;
+import java.io.File;
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.nio.channels.FileChannel;
+import java.nio.channels.FileLock;
+
+/** Use file locking to acquire a lock that will also block other processes. */
+class CrossProcessLock {
+  private final FileChannel channel;
+  private final FileLock lock;
+
+  private CrossProcessLock(FileChannel channel, FileLock lock) {
+    this.channel = channel;
+    this.lock = lock;
+  }
+
+  static CrossProcessLock acquire(Context appContext, String lockName) {
+    try {
+      File file = new File(appContext.getFilesDir(), lockName);
+      FileChannel channel = new RandomAccessFile(file, "rw").getChannel();
+      // Use the file channel to create a lock on the file.
+      // This method blocks until it can retrieve the lock.
+      FileLock lock = channel.lock();
+      return new CrossProcessLock(channel, lock);
+    } catch (IOException e) {
+      throw new IllegalStateException("exception while using file locks, should never happen", e);
+    }
+  }
+
+  /** Release a previously acquired lock and free any underlying resources. */
+  void releaseAndClose() {
+    try {
+      lock.release();
+      channel.close();
+    } catch (IOException e) {
+      throw new IllegalStateException("exception while using file locks, should never happen", e);
+    }
+  }
+}

firebase-installations/src/main/java/com/google/firebase/installations/FirebaseInstallations.java

@@ -33,11 +33,7 @@
 import com.google.firebase.installations.remote.InstallationResponse;
 import com.google.firebase.installations.remote.TokenResult;
 import com.google.firebase.platforminfo.UserAgentPublisher;
-import java.io.File;
 import java.io.IOException;
-import java.io.RandomAccessFile;
-import java.nio.channels.FileChannel;
-import java.nio.channels.FileLock;
 import java.util.ArrayList;
 import java.util.Calendar;
 import java.util.Iterator;
@@ -311,7 +307,8 @@ private final void doRegistrationInternal(boolean forceRefresh) {
    *     been persisted.
    */
   private PersistedInstallationEntry getPrefsWithGeneratedIdMultiProcessSafe() {
-    FileLock fileLock = getCrossProcessLock();
+    CrossProcessLock lock = CrossProcessLock
+        .acquire(firebaseApp.getApplicationContext(), LOCKFILE_NAME_GENERATE_FID);
     try {
       synchronized (lockGenerateFid) {
         PersistedInstallationEntry prefs =
@@ -332,30 +329,7 @@ private PersistedInstallationEntry getPrefsWithGeneratedIdMultiProcessSafe() {
       }
 
     } finally {
-      releaseCrossProcessLock(fileLock);
-    }
-  }
-
-  /** Use file locking to acquire a lock that will also block other processes. */
-  FileLock getCrossProcessLock() {
-    try {
-      File file =
-          new File(firebaseApp.getApplicationContext().getFilesDir(), LOCKFILE_NAME_GENERATE_FID);
-      FileChannel channel = new RandomAccessFile(file, "rw").getChannel();
-      // Use the file channel to create a lock on the file.
-      // This method blocks until it can retrieve the lock.
-      return channel.lock();
-    } catch (IOException e) {
-      throw new IllegalStateException("exception while using file locks, should never happen", e);
-    }
-  }
-
-  /** Release a previously acquired lock. */
-  void releaseCrossProcessLock(FileLock fileLock) {
-    try {
-      fileLock.release();
-    } catch (IOException e) {
-      throw new IllegalStateException("exception while using file locks, should never happen", e);
+      lock.releaseAndClose();
     }
   }