What are common mistakes developers make with happens-before relationships?

When it comes to managing concurrency in Java, understanding the happens-before relationship is crucial. However, developers often make several common mistakes, which can lead to unpredictable behavior in multi-threaded applications. Here are some of those mistakes:

• Neglecting the Java Memory Model: Developers might assume that visibility of shared mutable state is guaranteed between threads, which is not true without proper synchronization.
• Improper use of volatile: Using the 'volatile' modifier incorrectly can lead to missed updates in a multi-threaded environment.
• Failing to synchronize: Not using synchronized blocks or methods when modifying shared resources can cause data inconsistency.
• Over-synchronizing: Some developers sync too broadly, which can lead to performance bottlenecks and reduced concurrency.
• Assuming order of execution: Developers may expect certain threads to execute in a specific order, ignoring the possibilities of reordering by the JVM.

Understanding these pitfalls is key to writing correct and efficient concurrent code.