(翻译)理解并发的核心概念一

class Lazy <T> {
  private volatile T value;
  T get() {
    if (value == null)
      value = initialize();
    return value;
  }
}

class Waiter implements Runnable {
  private boolean shouldFinish;
  void finish() { shouldFinish = true; }
  public void run() {
    long iteration = 0;
    while (!shouldFinish) {
      iteration++;
    }
    System.out.println("Finished after: " + iteration);
  }
}
class DataRace {
  public static void main(String[] args) throws InterruptedException {
    Waiter waiter = new Waiter();
    Thread waiterThread = new Thread(waiter);
    waiterThread.start();
    waiter.finish();
    waiterThread.join();
  }
}

class AtomicOperation {
  private int counter0;
  private int counter1;
  void increment() {
    synchronized (this) {
      counter0++;
      counter1++;
    }
  }
}

class Reentrantcy {
  synchronized void doAll() {
    doFirst();
    doSecond();
  }
  synchronized void doFirst() {
    System.out.println("First operation is successful.");
  }
  synchronized void doSecond() {
    System.out.println("Second operation is successful.");
  }
}

class ConditionLoop {
  private boolean condition;
  synchronized void waitForCondition() throws InterruptedException {
    while (!condition) {
      wait();
    }
  }
  synchronized void satisfyCondition() {
    condition = true;
    notifyAll();
  }
}

class VolatileFlag implements Runnable {
  private volatile boolean shouldStop;
  public void run() {
    while (!shouldStop) {
      //do smth
    }
    System.out.println("Stopped.");
  }
  void stop() {
    shouldStop = true;
  }
  public static void main(String[] args) throws InterruptedException {
    VolatileFlag flag = new VolatileFlag();
    Thread thread = new Thread(flag);
    thread.start();
    flag.stop();
    thread.join();
  }
}

class CheckThenAct {
  private final AtomicReference<String> value = new AtomicReference<>();
  void initialize() {
    if (value.compareAndSet(null, "Initialized value")) {
      System.out.println("Initialized only once.");
    }
  }
}

class Increment {
  private final AtomicInteger state = new AtomicInteger();
  void advance() {
    int oldState = state.getAndIncrement();
    System.out.println("Advanced: '" + oldState + "' -> '" + (oldState + 1) + "'.");
  }
}

class TransactionManager {
  private final ThreadLocal<Transaction> currentTransaction 
      = ThreadLocal.withInitial(NullTransaction::new);
  Transaction currentTransaction() {
    Transaction current = currentTransaction.get();
    if (current.isNull()) {
      current = new TransactionImpl();
      currentTransaction.set(current);
    }
    return current;
  }
}

class StaticInitializer {
  // Publishing an immutable object without additional initialization
  public static final Year year = Year.of(2017); 
  public static final Set<String> keywords;
  // Using static initializer to construct a complex object
  static {
    // Creating mutable set
    Set<String> keywordsSet = new HashSet<>(); 
    // Initializing state
    keywordsSet.add("java");
    keywordsSet.add("concurrency");
    // Making set unmodifiable 
    keywords = Collections.unmodifiableSet(keywordsSet); 
  }
}

class Volatile {
  private volatile String state;
  void setState(String state) {
    this.state = state;
  }
  String getState() {
    return state; 
  }
}

class Atomics {
  private final AtomicInteger state = new AtomicInteger();
  void initializeState(int state) {
    this.state.compareAndSet(0, state);
  }
  int getState() {
    return state.get();
  }
}

class Final {
  private final String state;
  Final(String state) {
    this.state = state;
  }
  String getState() {
    return state;
  }
}

class ThisEscapes {
 private final String name;
 ThisEscapes(String name) {
   Cache.putIntoCache(this);
   this.name = name;
 }
 String getName() { return name; }
}
class Cache {
 private static final Map<String, ThisEscapes> CACHE = new ConcurrentHashMap<>();
 static void putIntoCache(ThisEscapes thisEscapes) {
   // 'this' reference escaped before the object is fully constructed.
   CACHE.putIfAbsent(thisEscapes.getName(), thisEscapes);
 }
}

class Synchronization {
  private String state;
  synchronized String getState() {
    if (state == null)
      state = "Initial";
    return state;
  }
}

// Marked as final - subclassing is forbidden
public final class Artist {
  // Immutable object, field is final
  private final String name; 
  // Collection of immutable objects, field is final
  private final List<Track> tracks; 
  public Artist(String name, List<Track> tracks) {
    this.name = name;
    // Defensive copy
    List<Track> copy = new ArrayList<>(tracks); 
    // Making mutable collection unmodifiable
    this.tracks = Collections.unmodifiableList(copy); 
    // 'this' is not passed to anywhere during construction
  }
  // Getters, equals, hashCode, toString
}
// Marked as final - subclassing is forbidden
public final class Track { 
  // Immutable object, field is final
  private final String title; 
  public Track(String title) {
    this.title = title;
  }
  // Getters, equals, hashCode, toString
}

Thread thread = new Thread(runnable);
thread.setUncaughtExceptionHandler((failedThread, exception) -> {
  logger.error("Caught unexpected exception in thread '{}'.",
      failedThread.getName(), exception);
});
thread.start();