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The assumption that thread suspension and yielding flush the cached registers and reload the values when execution resumes, is misleading and paves the way for potential coding errors.

The {{Thread.getState()}} method returns the current state of a thread. Using this method for synchronization control such as checking whether a thread is blocked on a wait is inappropriate because a blocked thread is not always required to enter the {{WAITING}} or {{TIMED_WAITING}} state in cases where the JVM chooses to implement the blocking using spin-waiting \[[Goetz 06|AA. Java References#Goetz 06]\].

Noncompliant Code Example

This noncompliant code example declares a nonvolatile Boolean flag.

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"The compiler is free to read the field {{this.done}} just once, and reuse the cached value in each execution of the loop. This would mean that the loop would never terminate, even if another thread changed the value of {{this.done}}." \[[JLS 05|AA. Java References#JLS 05]\]. This occurs because {{Thread.sleep()}} does not establish a [happens-before|BB. Definitions#happens-before order] relation.

Compliant Solution

This compliant solution declares the flag volatile to ensure that updates to it are made visible across multiple threads.

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The volatile flag establishes a happens-before relation between any thread that sets done and this thread.

Risk Assessment

Relying on the synchronization semantics of Thread.yield() and Thread.sleep() methods can cause unexpected behavior.

Automated Detection

TODO

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

References

\[[JLS 05|AA. Java References#JLS 05]\] section 17.9 "Sleep and Yield"

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