Chapter 1: Protect Your Shared Mutable State

Document for Concurrency 

class Counter {

  private long count;

  synchronized void increment(long amount) {
    if (amount < 1) {
      throw new IllegalArgumentException("Only increments!");
    }

    this.count += amount;
  }
}
  • Knowing if a method is thread safe is very important!
  • Without documentation, it takes some time to figure out if it really is thread-safe

/** thread safe */
class Counter {

  /** guarded by 'this' */
  private long count;

  synchronized void increment(long amount) {
    if (amount < 1) {
      throw new IllegalArgumentException("Only increments!");
    }

    this.count += amount;
  }
}
  • comments similar to the annotations from Java Concurrency in Practice
  • help to safely use the classes
  • multiple variants: thread-safe, immutable, conditionally thread-safe, not thread-safe