Synchronized Methods in Kotlin

Multithreading is a powerful tool that enables developers to create efficient and responsive applications that can perform multiple tasks simultaneously. However, multithreading also introduces the risk of race conditions and other concurrency issues that can cause unexpected behavior and crashes in our applications.

To ensure thread safety and prevent these issues, Kotlin provides a synchronized keyword that allows us to synchronize access to shared resources and ensure that only one thread can access a critical section at a time.

How to use synchronized methods in Kotlin

To use synchronized methods in Kotlin, we need to define a synchronized block of code that will be executed atomically by a single thread at a time. We can do this by using the synchronized keyword followed by the object we want to synchronize on, like this:

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1class Counter {
2    private var count = 0
3
4    fun increment() {
5        synchronized(this) {
6            count++
7        }
8    }
9
10    fun getCount(): Int {
11        synchronized(this) {
12            return count
13        }
14    }
15}

In this example, we have defined a Counter class that contains two methods: increment() and getCount(). Both methods are synchronized using the synchronized keyword followed by the this keyword, which refers to the current instance of the class.

By synchronizing these methods, we ensure that only one thread can access the count variable at a time, preventing race conditions and other concurrency issues.

Using synchronized blocks with custom locks

In some cases, we may need to use a custom lock object instead of the this keyword. We can do this by defining a separate lock object and using it in our synchronized block, like this:

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1class Database {
2    private val lock = Any()
3
4    fun readData() {
5        synchronized(lock) {
6            // Read data from database
7        }
8    }
9
10    fun writeData() {
11        synchronized(lock) {
12            // Write data to database
13        }
14    }
15}

In this example, we have defined a Database class that contains two methods: readData() and writeData(). Both methods are synchronized using a custom lock object named lock, which is defined as a private property of the class.

By using a custom lock object, we can ensure that only one thread can access the database at a time, regardless of how many instances of the Database class are created.

Conclusion

In conclusion, synchronized methods in Kotlin provide a powerful tool for ensuring thread safety and preventing race conditions and other concurrency issues in our applications. By synchronizing access to shared resources using the synchronized keyword, we can ensure that only one thread can access a critical section at a time, preventing unexpected behavior and crashes in our applications.

Remember to use synchronized methods judiciously, as they can introduce performance overhead and may not be necessary in all cases. With careful use, however, synchronized methods can help us create efficient and responsive multithreaded applications that provide a great user experience.