| /* |
| * Copyright (C) 2014 The Android Open Source Project |
| * |
| * 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.android.printspooler.model; |
| |
| import android.util.Log; |
| |
| import java.io.File; |
| import java.io.IOException; |
| |
| /** |
| * This class provides a shared file to several threads. Only one thread |
| * at a time can use the file. To acquire the file a thread has to |
| * request it in a blocking call to {@link #acquireFile(OnReleaseRequestCallback)}. |
| * The provided callback is optional and is used to notify the owning thread |
| * when another one wants to acquire the file. In case a release is requested |
| * the thread owning the file must release it as soon as possible. If no |
| * callback is provided a thread that acquires the file must release it |
| * as soon as possible, i.e. even if callback was provided the thread cannot |
| * have the file for less time. |
| */ |
| public final class MutexFileProvider { |
| private static final String LOG_TAG = "MutexFileProvider"; |
| |
| private static final boolean DEBUG = true; |
| |
| private final Object mLock = new Object(); |
| |
| private final File mFile; |
| |
| private Thread mOwnerThread; |
| |
| private OnReleaseRequestCallback mOnReleaseRequestCallback; |
| |
| public interface OnReleaseRequestCallback { |
| public void onReleaseRequested(File file); |
| } |
| |
| public MutexFileProvider(File file) throws IOException { |
| mFile = file; |
| if (file.exists()) { |
| file.delete(); |
| } |
| file.createNewFile(); |
| } |
| |
| public File acquireFile(OnReleaseRequestCallback callback) { |
| synchronized (mLock) { |
| // If this thread has the file, nothing to do. |
| if (mOwnerThread == Thread.currentThread()) { |
| return mFile; |
| } |
| |
| // Another thread wants file ask for a release. |
| if (mOwnerThread != null && mOnReleaseRequestCallback != null) { |
| mOnReleaseRequestCallback.onReleaseRequested(mFile); |
| } |
| |
| // Wait until the file is released. |
| while (mOwnerThread != null) { |
| try { |
| mLock.wait(); |
| } catch (InterruptedException ie) { |
| /* ignore */ |
| } |
| } |
| |
| // Update the owner and the callback. |
| mOwnerThread = Thread.currentThread(); |
| mOnReleaseRequestCallback = callback; |
| |
| if (DEBUG) { |
| Log.i(LOG_TAG, "Acquired file: " + mFile + " by thread: " + mOwnerThread); |
| } |
| |
| return mFile; |
| } |
| } |
| |
| public void releaseFile() { |
| synchronized (mLock) { |
| if (mOwnerThread != Thread.currentThread()) { |
| return; |
| } |
| |
| if (DEBUG) { |
| Log.i(LOG_TAG, "Released file: " + mFile + " from thread: " + mOwnerThread); |
| } |
| |
| // Update the owner and the callback. |
| mOwnerThread = null; |
| mOnReleaseRequestCallback = null; |
| |
| mLock.notifyAll(); |
| } |
| } |
| } |