'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;
    }
  }

Locating this inspection

By ID

Can be used to locate inspection in e.g. Qodana configuration files, where you can quickly enable or disable it, or adjust its settings.

WhileLoopSpinsOnField

Via Settings dialog

Path to the inspection settings via IntelliJ Platform IDE Settings dialog, when you need to adjust inspection settings directly from your IDE.

Settings or Preferences | Editor | Inspections | Java | Threading issues

Use the inspection options to only report empty while loops.

Inspection options

Here you can find the description of settings available for the 'while' loop spins on field inspection, and the reference of their default values.

Only warn if the loop is empty: Default: Selected

Inspection Details
By default bundled with:	IntelliJ IDEA 2024.2, Qodana for JVM 2024.2,
Can be installed with plugin:	Java, 242.22892

Last modified: 11 September 2024