Non Thread Safe Shared State (ARCH4038)

Key java.async.non-volatile-shared-field · Severity warning · Category async

Mutable shared fields that are not volatile/atomic and are read or written outside a synchronized block cause visibility issues and race conditions under concurrent access.

Incorrect

class Counter {
    private boolean running;          // shared, unprotected
    void start() { running = true; }
    void stop()  { running = false; } // from another thread
}

Correct

class Counter {
    private volatile boolean running; // visibility guaranteed
    void start() { running = true; }
    void stop()  { running = false; }
}

Fix

Make the shared field volatile, use an AtomicX type, or guard every access with synchronized/a lock.