Synchronized method in android

Synchronized Methods in Android

Synchronized methods in Android are a crucial mechanism for ensuring thread safety in multithreaded applications. When multiple threads access shared resources concurrently, data corruption and unexpected behavior can occur. Synchronized methods provide a way to control access to these shared resources, preventing race conditions and ensuring data integrity.

Understanding Synchronization

What is Thread Safety?

Thread safety refers to the ability of a piece of code to be executed concurrently by multiple threads without causing unexpected results. When threads access shared resources without proper synchronization, it can lead to data inconsistency, race conditions, and other issues.

Race Conditions

A race condition occurs when multiple threads access and modify shared resources simultaneously, resulting in an unpredictable outcome depending on the order of execution. To illustrate, imagine two threads trying to increment a shared counter:

// Shared counter
int counter = 0;

// Thread 1
counter++;

// Thread 2
counter++;

If both threads execute these lines simultaneously, the final value of ‘counter’ might be 1 or 2 instead of the expected 2. This unpredictability arises due to the race condition.

Synchronized Methods: The Solution

Synchronized methods in Java (and thus Android) provide a way to enforce mutual exclusion, ensuring that only one thread can access a shared resource at a time.

The ‘synchronized’ Keyword

The ‘synchronized’ keyword in Java acts as a lock mechanism. When a method is declared as ‘synchronized’, the JVM automatically acquires a lock associated with the object on which the method is invoked. This lock prevents other threads from executing the same method on the same object until the current thread releases the lock.

Example

Let’s modify the previous counter example using a synchronized method:

class Counter {
  private int counter = 0;

  public synchronized void increment() {
    counter++;
  }
}

// Usage
Counter c = new Counter();
Thread t1 = new Thread(() -> c.increment());
Thread t2 = new Thread(() -> c.increment());
t1.start();
t2.start();

// Output: 2

In this example, the ‘increment()’ method is declared ‘synchronized’. When a thread enters the method, it acquires the lock on the ‘c’ object. Any other thread trying to invoke ‘increment()’ on the same ‘c’ object will be blocked until the current thread finishes execution and releases the lock.

Synchronization Techniques

Synchronized Methods vs. Blocks

Re-entrant Locks

Synchronized methods in Java are re-entrant locks. This means that if a thread acquires a lock on an object, it can re-enter the synchronized method on the same object without blocking. This behavior is essential for avoiding deadlocks and ensuring thread safety in nested synchronized methods.

Benefits and Considerations

Benefits of Synchronization

• Thread Safety: Prevents race conditions and ensures data consistency in multithreaded applications.
• Resource Protection: Guarantees exclusive access to shared resources, preventing conflicts.

Considerations

• Performance Overhead: Synchronized methods can introduce overhead due to locking and unlocking operations.
• Deadlock Potential: Incorrect usage of synchronized methods can lead to deadlocks, where threads indefinitely wait for each other to release locks.

Alternatives to Synchronization

While synchronized methods are essential for thread safety, there are alternative techniques you can explore in Android development:

• Atomic Operations: Java provides atomic operations (e.g., ‘AtomicInteger’) that offer thread safety without requiring explicit synchronization.
• Concurrent Collections: Java’s concurrent collections (e.g., ‘ConcurrentHashMap’) are designed for thread-safe operations without requiring manual synchronization.

Conclusion

Synchronized methods in Android provide a fundamental mechanism for ensuring thread safety and data integrity in multithreaded environments. Understanding synchronization is crucial for building reliable and efficient Android applications. By carefully applying synchronized methods and exploring alternative techniques, you can manage concurrency effectively and avoid the pitfalls of multithreading.