Override Drops Parent Synchronization

ID

java.override_drops_synchronized

Severity

high

Remediation Complexity

trivial

Remediation Risk

medium

Remediation Effort

low

Resource

Reliability

Language

Java

Tags

reliability

Description

Reports a method that overrides a synchronized method declared in its direct parent class without itself being synchronized, and without an equivalent synchronized block wrapping its whole body.

Only the direct parent is examined; a grandparent’s synchronized method is out of scope. A parent method that is private, or that differs from the override by the static modifier, is not a real override relationship and is not compared. The reverse case — an override that adds synchronized over a parent that does not have it — is not reported.

Rationale

Callers of the parent type rely on the thread-safety its synchronized contract promised. An override that drops the modifier still compiles, still overrides correctly, and still satisfies every functional test — but silently removes that guarantee for every caller who reaches the method through the parent’s type.

public class Cache {
  public synchronized void invalidate() {
    // ...
  }
}

public class LoggingCache extends Cache {
  @Override
  public void invalidate() { // no longer thread-safe
    // ...
  }
}

Remediation

Keep the override synchronized, either with the modifier or with a synchronized block that wraps the whole method body:

public class LoggingCache extends Cache {
  @Override
  public synchronized void invalidate() {
    // ...
  }
}

References

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