1 /* 2 * Copyright (C) 2016 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package com.android.documentsui.clipping; 18 19 import android.net.Uri; 20 21 import java.io.Closeable; 22 import java.io.File; 23 import java.io.FileInputStream; 24 import java.io.IOException; 25 import java.nio.channels.FileLock; 26 import java.util.HashMap; 27 import java.util.Map; 28 import java.util.Scanner; 29 30 /** 31 * Reader class used to read uris from clip files stored in {@link ClipStorage}. It provides 32 * synchronization within a single process as an addition to {@link FileLock} which is for 33 * cross-process synchronization. 34 */ 35 class ClipStorageReader implements Iterable<Uri>, Closeable { 36 37 /** 38 * FileLock can't be held multiple times in a single JVM, but it's possible to have multiple 39 * readers reading the same clip file. Share the FileLock here so that it can be released 40 * when it's not needed. 41 */ 42 private static final Map<String, FileLockEntry> sLocks = new HashMap<>(); 43 44 private final String mCanonicalPath; 45 private final Scanner mScanner; 46 ClipStorageReader(File file)47 ClipStorageReader(File file) throws IOException { 48 FileInputStream inStream = new FileInputStream(file); 49 mScanner = new Scanner(inStream); 50 51 mCanonicalPath = file.getCanonicalPath(); // Resolve symlink 52 synchronized (sLocks) { 53 if (sLocks.containsKey(mCanonicalPath)) { 54 // Read lock is already held by someone in this JVM, just increment the ref 55 // count. 56 sLocks.get(mCanonicalPath).mCount++; 57 } else { 58 // No map entry, need to lock the file so it won't pass this line until the 59 // corresponding writer is done writing. 60 FileLock lock = inStream.getChannel().lock(0L, Long.MAX_VALUE, true); 61 sLocks.put(mCanonicalPath, new FileLockEntry(1, lock, mScanner)); 62 } 63 } 64 } 65 66 @Override iterator()67 public Iterator iterator() { 68 return new Iterator(mScanner); 69 } 70 71 @Override close()72 public void close() throws IOException { 73 FileLockEntry ref; 74 synchronized (sLocks) { 75 ref = sLocks.get(mCanonicalPath); 76 77 assert(ref.mCount > 0); 78 if (--ref.mCount == 0) { 79 // If ref count is 0 now, then there is no one who needs to hold the read lock. 80 // Release the lock, and remove the entry. 81 ref.mLock.release(); 82 ref.mScanner.close(); 83 sLocks.remove(mCanonicalPath); 84 } 85 } 86 87 if (mScanner != ref.mScanner) { 88 mScanner.close(); 89 } 90 } 91 92 private static final class Iterator implements java.util.Iterator { 93 private final Scanner mScanner; 94 Iterator(Scanner scanner)95 private Iterator(Scanner scanner) { 96 mScanner = scanner; 97 } 98 99 @Override hasNext()100 public boolean hasNext() { 101 return mScanner.hasNextLine(); 102 } 103 104 @Override next()105 public Uri next() { 106 String line = mScanner.nextLine(); 107 return Uri.parse(line); 108 } 109 } 110 111 private static final class FileLockEntry { 112 private final FileLock mLock; 113 // We need to keep this scanner here because if the scanner is closed, the file lock is 114 // closed too. 115 private final Scanner mScanner; 116 117 private int mCount; 118 FileLockEntry(int count, FileLock lock, Scanner scanner)119 private FileLockEntry(int count, FileLock lock, Scanner scanner) { 120 mCount = count; 121 mLock = lock; 122 mScanner = scanner; 123 } 124 } 125 } 126