SynchronizedReadObjectMethod.md

Pattern: Use of synchronized readObject()

Issue: -

Description

Catches Serializable classes that define a synchronized readObject() method. By definition, an object created by deserialization is only reachable by one thread, and thus there is no need for readObject() to be synchronized. If the readObject() method itself is causing the object to become visible to another thread, that is an example of very dubious coding style.

Examples:

class SomeClass implements Serializable {

    private synchronized void readObject(ObjectInputStream input) throws IOException, ClassNotFoundException {
        // violation, no need to synchronized
    }
}

class SomeClass implements Serializable {

    private void readObject(ObjectInputStream input) throws IOException, ClassNotFoundException {
        synchronized(lock) {
            // violation, no need to synchronized
        }
    }
}

// OK, class not Serializable
class SomeClass {

    private synchronized void readObject(ObjectInputStream input) throws IOException, ClassNotFoundException { }
}

// OK, class not Serializable
class SomeClass {

    private void readObject(ObjectInputStream input) throws IOException, ClassNotFoundException {
        synchronized(lock) { }
    }
}

class SomeClass implements Serializable {

    private void readObject(ObjectInputStream input) throws IOException, ClassNotFoundException {
        // OK, this block is more than just a simple sync statement
        synchronized(lock) { }
        doSomething()
    }
}

Further Reading

• CodeNarc - SynchronizedReadObjectMethod