To make a piece of code thread safe, you can follow these techniques:
1. Synchronization
- Synchronized Method
: The JVM (Java Virtual Machine) ensures that only one thread can execute that method for a given object at any moment. It’s like having a single-use key that only one person can use to enter a room.
java
public synchronized void increment() {
// code here can only be executed by one thread at a time
}
* Synchronized Block
: A synchronized block allows you to specify a section of code that should be synchronized, rather than the entire method. It’s like having a key to a specific part of a building, instead of the whole building.
java
public void increment() {
synchronized(this) {
// only one thread can execute this block at a time
}
}
2. Locks
Locks are objects used to control access to shared resources among multiple threads. They provide more control and flexibility compared to synchronized methods and blocks.
You explicitly acquire and release a lock to control access. Think of a public computer with a sign-up sheet. If you want to use it, you need to sign up (acquire the lock). After you’re done, you sign off (release the lock) so others can use it.
private final ReentrantLock lock = new ReentrantLock();
public void increment() {
lock.lock();
try {
// critical section of code
} finally {
lock.unlock(); // make sure to unlock in the finally block
}
3. Volatile Keyword
Volatile keyword ensures visibility of changes to variables across threads. You can declare a variable as volatile to make its changes immediately visible to other threads.
private volatile boolean flag = true;
4. Atomic Variables
Atomic variables ensure thread-safe operations on single variables without using explicit synchronization.
private AtomicInteger counter = new AtomicInteger();
public void increment() {
counter.incrementAndGet();
}
Summary
- Synchronized Methods: Control access to the entire method. Simple but can be less flexible.
- Synchronized Blocks: Control access to specific sections of code within a method. More precise control.
- Locks: Provide explicit and flexible control over synchronization, allowing for more complex coordination.
- Atomic variable: Atomic variables are like a special kind of counter that automatically updates itself in a thread-safe way, much like a digital scoreboard that safely counts points without needing a manual reset.
Things to keep in mind while doing so
-
Deadlock Prevention:
Ensure locks are acquired and released in a consistent order to avoid deadlocks. * #### Minimize Synchronized Blocks:
Keep synchronized blocks as short as possible to reduce contention and improve performance.
Follow-Up Questions
What is a deadlock in multithreading?
A deadlock occurs when two or more threads wait indefinitely for each other to release resources. It can be avoided by acquiring locks in a consistent order and using timeout mechanisms.
What is the difference between synchronized method and synchronized block?
A synchronized method locks the whole method, while a synchronized block only locks a specific section of code, providing finer control over synchronization.
Why is it important to keep synchronized blocks short?
To reduce contention and improve the performance of the application by minimizing the time threads spend waiting for locks.