'while' loop spins on field

Reports while loops that spin on the value of a non-volatile field, waiting for it to be changed by another thread.

In addition to being potentially extremely CPU intensive when little work is done inside the loop, such loops are likely to have different semantics from what was intended. The Java Memory Model allows such loops to never complete even if another thread changes the field's value.

Additionally, since Java 9 it's recommended to call Thread.onSpinWait() inside a spin loop on a volatile field, which may significantly improve performance on some hardware.

Example:

class SpinsOnField {
  boolean ready = false;

  void run() {
    while (!ready) {
    }
    // do some work
  }

  void markAsReady() {
    ready = true;
  }
}

After the quick-fix is applied:

class SpinsOnField {
  volatile boolean ready = false;

  void run() {
    while (!ready) {
      Thread.onSpinWait();
    }
    // do some work
  }

  void markAsReady() {
    ready = true;
  }
}

Use the inspection options to only report empty while loops.

Inspection options

Option	Type	Default
Only warn if the loop is empty	Checkbox	true

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

Last modified: 13 July 2023