Deadlocks and Synchronization Pitfalls

Deadlock conditions

If all four conditions hold simultaneously, deadlock can happen. Breaking any one condition helps prevention.

• Mutual exclusion
• Hold and wait
• No preemption
• Circular wait

Simple lock ordering strategy

Object lockA = new Object();
Object lockB = new Object();

// Always acquire A then B in every thread.
synchronized (lockA) {
  synchronized (lockB) {
    // critical section
  }
}