What is Thread Synchronization in Android?

Copy codevar counter = 0

// Thread 1 and Thread 2 both do this:
counter++  // Not atomic! Read -> Increment -> Write

// Without sync, final counter might be 1 instead of 2

Copy code@Synchronized
fun incrementCounter() {
    counter++
}

Copy codefun incrementCounter() {
    synchronized(this) {
        counter++
    }
}

Copy code@Volatile
var isRunning = true

Copy codeval atomicCounter = AtomicInteger(0)
atomicCounter.incrementAndGet()  // Thread-safe

Copy codeval lock = ReentrantLock()

fun safeOperation() {
    lock.lock()
    try {
        // Critical section
    } finally {
        lock.unlock()
    }
}

Copy codeval mutex = Mutex()

suspend fun safeOperation() {
    mutex.withLock {
        // Critical section
    }
}

Copy codeWithout Sync:
Thread1: Read(0) -> Add -> Write(1)
Thread2:    Read(0) -> Add -> Write(1)  // Lost update!
Result: 1 (expected 2)

With Sync:
Thread1: Lock -> Read(0) -> Add -> Write(1) -> Unlock
Thread2:                                        Lock -> Read(1) -> Add -> Write(2) -> Unlock
Result: 2 ✓