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| 1 | +package br.com.leonardoz.features.collections; |
| 2 | + |
| 3 | +import java.util.Random; |
| 4 | +import java.util.UUID; |
| 5 | +import java.util.concurrent.BlockingQueue; |
| 6 | +import java.util.concurrent.ConcurrentHashMap; |
| 7 | +import java.util.concurrent.CopyOnWriteArrayList; |
| 8 | +import java.util.concurrent.LinkedBlockingQueue; |
| 9 | + |
| 10 | +/** |
| 11 | + * Concurrent collections are an alternative to the Synchronized Collections. |
| 12 | + * |
| 13 | + * Supports concurrent access from n threads and performs better than |
| 14 | + * Synchronized collections. |
| 15 | + * |
| 16 | + */ |
| 17 | +public class UsingConcurrentCollections { |
| 18 | + |
| 19 | + /** |
| 20 | + * Map for Concurrent access. Sacrifices some aspects of synchronization to |
| 21 | + * achieve better performance. |
| 22 | + * |
| 23 | + * Locks it's values with Lock Striping. |
| 24 | + * |
| 25 | + * Lock Striping divides the protected region through several locks. |
| 26 | + * |
| 27 | + * - Don't throw ConcurrentModificationException |
| 28 | + * |
| 29 | + * - size() and isEmpty() can be incorrect. Don't relly on then. |
| 30 | + * |
| 31 | + * - Supports atomic operations, doen't neet client side locking. |
| 32 | + * |
| 33 | + * - Readers can access concurrently, and iterator have weak consistency. |
| 34 | + * |
| 35 | + * - Just a few Writers can modify it. |
| 36 | + */ |
| 37 | + public static void usingConcurrentHashMap() { |
| 38 | + System.out.println("=== ConcurrentHashMap ==="); |
| 39 | + Random random = new Random(); |
| 40 | + ConcurrentHashMap<UUID, Integer> valuesPerUuid = new ConcurrentHashMap<>(); |
| 41 | + // atomic operations |
| 42 | + valuesPerUuid.putIfAbsent(UUID.randomUUID(), random.nextInt(100)); |
| 43 | + |
| 44 | + // simulating concurrent access - no duplicates should be inserted |
| 45 | + for (int i = 0; i < 100; i++) { |
| 46 | + if (i % 6 == 0) { |
| 47 | + // write |
| 48 | + new Thread(() -> { |
| 49 | + UUID uuid = UUID.randomUUID(); |
| 50 | + Integer value = random.nextInt(10); |
| 51 | + System.out.println("Added " + uuid + " - " + value); |
| 52 | + valuesPerUuid.putIfAbsent(uuid, value); |
| 53 | + }).start(); |
| 54 | + } else { |
| 55 | + // read |
| 56 | + new Thread(() -> System.out.println("Printed " + valuesPerUuid.values().toString())).start(); |
| 57 | + } |
| 58 | + } |
| 59 | + try { |
| 60 | + // space for other examples |
| 61 | + Thread.sleep(2000); |
| 62 | + System.out.println("\n\n\n\n"); |
| 63 | + } catch (InterruptedException e) { |
| 64 | + e.printStackTrace(); |
| 65 | + } |
| 66 | + } |
| 67 | + |
| 68 | + /** |
| 69 | + * Replacement for synchronized list. Based on the immutable object concept. |
| 70 | + * |
| 71 | + * Use when reading is far more common than writing. |
| 72 | + * |
| 73 | + * Creates a new copy every time that the list is modified, only synchronizing |
| 74 | + * briefly to ensure array content visibility. |
| 75 | + * |
| 76 | + * iterator returns a snapshot of the current state of the collection. |
| 77 | + * |
| 78 | + * Supports atomic operations. |
| 79 | + * |
| 80 | + */ |
| 81 | + public static void usingCopyOnWriteArrayList() { |
| 82 | + System.out.println("=== CopyOnWriteArrayList ==="); |
| 83 | + Random random = new Random(); |
| 84 | + // No ConcurrentModificationException |
| 85 | + CopyOnWriteArrayList<Integer> copyOnWriteArrayList = new CopyOnWriteArrayList<Integer>(); |
| 86 | + |
| 87 | + for (int i = 0; i < 100; i++) { |
| 88 | + if (i % 8 == 0) { |
| 89 | + // write |
| 90 | + new Thread(() -> { |
| 91 | + Integer value = random.nextInt(10); |
| 92 | + System.err.println("Added " + value); |
| 93 | + copyOnWriteArrayList.add(value); |
| 94 | + }).start(); |
| 95 | + } else { |
| 96 | + // read |
| 97 | + new Thread(() -> { |
| 98 | + StringBuilder sb = new StringBuilder(); |
| 99 | + for (Integer vv : copyOnWriteArrayList) { |
| 100 | + sb.append(vv + " "); |
| 101 | + } |
| 102 | + System.out.println("Reading " + sb.toString()); |
| 103 | + }).start(); |
| 104 | + } |
| 105 | + } |
| 106 | + try { |
| 107 | + // space for other examples |
| 108 | + Thread.sleep(2000); |
| 109 | + System.out.println("\n\n\n\n"); |
| 110 | + } catch (InterruptedException e) { |
| 111 | + e.printStackTrace(); |
| 112 | + } |
| 113 | + } |
| 114 | + |
| 115 | + /** |
| 116 | + * Concurrent Queue interface. |
| 117 | + * |
| 118 | + * Implementations: LinkedBlockingQueue, ArrayBlockingQueue, |
| 119 | + * PriorirtBlockingQueue, SynchronizedQueue. |
| 120 | + * |
| 121 | + * Used for the Producer-Consumer pattern. |
| 122 | + * |
| 123 | + * Blocking methods: put/take; Timed blocking methods: offer, poll; |
| 124 | + * |
| 125 | + * Can be bounded or unbounded. |
| 126 | + * |
| 127 | + */ |
| 128 | + public static void usingBlockingQueue() { |
| 129 | + System.out.println("=== BlockingQueue ==="); |
| 130 | + |
| 131 | + // Bounded UUID queue |
| 132 | + BlockingQueue<UUID> uuidQueue = new LinkedBlockingQueue<>(10); |
| 133 | + |
| 134 | + System.out.println("Queue will execute for 10s"); |
| 135 | + |
| 136 | + // Multiple consumers |
| 137 | + Runnable runConsumer = () -> { |
| 138 | + while (!Thread.currentThread().isInterrupted()) { |
| 139 | + try { |
| 140 | + UUID uuid = uuidQueue.take(); |
| 141 | + System.out.println("Consumed: " + uuid + " by " + Thread.currentThread().getName()); |
| 142 | + |
| 143 | + } catch (InterruptedException e) { |
| 144 | + // interrupted pattern |
| 145 | + System.err.println("Consumer Finished"); |
| 146 | + } |
| 147 | + } |
| 148 | + }; |
| 149 | + Thread consumer1 = new Thread(runConsumer); |
| 150 | + consumer1.start(); |
| 151 | + Thread consumer2 = new Thread(runConsumer); |
| 152 | + consumer2.start(); |
| 153 | + |
| 154 | + // Producer Thread |
| 155 | + Runnable runProducer = () -> { |
| 156 | + try { |
| 157 | + while (!Thread.currentThread().isInterrupted()) { |
| 158 | + Random r = new Random(); |
| 159 | + // Delay producer |
| 160 | + Thread.sleep(r.nextInt(1000)); |
| 161 | + UUID randomUUID = UUID.randomUUID(); |
| 162 | + System.out.println("Produced: " + randomUUID + " by " + Thread.currentThread().getName()); |
| 163 | + uuidQueue.put(randomUUID); |
| 164 | + } |
| 165 | + } catch (InterruptedException e) { |
| 166 | + // interrupted pattern |
| 167 | + System.err.println("Producer Finished"); |
| 168 | + } |
| 169 | + }; |
| 170 | + |
| 171 | + // Multiple producers |
| 172 | + Thread producer1 = new Thread(runProducer); |
| 173 | + producer1.start(); |
| 174 | + Thread producer2 = new Thread(runProducer); |
| 175 | + producer2.start(); |
| 176 | + Thread producer3 = new Thread(runProducer); |
| 177 | + producer3.start(); |
| 178 | + |
| 179 | + try { |
| 180 | + // Queue will run for 10secs |
| 181 | + Thread.sleep(10000); |
| 182 | + producer1.interrupt(); |
| 183 | + producer2.interrupt(); |
| 184 | + producer3.interrupt(); |
| 185 | + consumer1.interrupt(); |
| 186 | + consumer2.interrupt(); |
| 187 | + |
| 188 | + } catch (InterruptedException e) { |
| 189 | + e.printStackTrace(); |
| 190 | + } |
| 191 | + } |
| 192 | + |
| 193 | + public static void main(String[] args) { |
| 194 | + usingConcurrentHashMap(); |
| 195 | + usingCopyOnWriteArrayList(); |
| 196 | + usingBlockingQueue(); |
| 197 | + } |
| 198 | + |
| 199 | +} |
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