Double-checked locking

Reports double-checked locking.

Double-checked locking tries to initialize a field on demand and in a thread-safe manner, while avoiding the cost of synchronization. Unfortunately it is not thread-safe when used on a field that is not declared volatile. When using Java 1.4 or earlier, double-checked locking doesn't work even with a volatile field. Read the article linked above for a detailed explanation of the problem.

Example of incorrect double-checked locking:

class Foo {
  private Helper helper = null;
  public Helper getHelper() {
    if (helper == null)
      synchronized(this) {
        if (helper == null) helper = new Helper();
      }
      return helper;
    }
  }
  // other functions and members...
}

Inspection Details
Available in:	IntelliJ IDEA 2023.3, Qodana for JVM 2023.3
Plugin:	Java, 233.SNAPSHOT

Last modified: 13 July 2023