What is thread safety in Java parallel programming? How to achieve?

Thread safety in Java refers to the correct access of code in a multi-threaded environment to prevent concurrency problems. Several ways to achieve thread safety are: Synchronized code blocks: Use the synchronized keyword to mark code that only allows one thread to access it at a time. Mutex lock: Use a Lock object to lock a code segment to ensure that only one thread can access it at a time. Atomic variables: Use atomic variables (such as AtomicInteger) to save values, and updates to the values ​​are atomic. Immutable objects: Use immutable objects because they cannot be modified and do not require synchronization.

Thread safety in Java parallel programming

In a multi-threaded environment, thread safety means that the code can be used by multiple threads access simultaneously without producing errors or inconsistent results. Implementing thread safety is critical to preventing concurrency issues.

How to achieve thread safety

There are several ways to achieve thread safety:

• Synchronized code block: Use the synchronized keyword to mark a block of code so that it can only be accessed by one thread at a time.
• Mutex lock (Lock): Use a Lock object to lock a code section to ensure that only one thread can access it at a time.
• Atomic variables: Use atomic variables (such as AtomicInteger) to save values, and the update operation of the value is atomic, that is, either all or all Not executed.
• Immutable objects: Use immutable objects because they cannot be modified and therefore do not require additional synchronization mechanisms.

Practical case

Consider a class Counter, which has an integer field count. We need to implement a thread-safe increment method to increment this field.

Unsafe implementation:

public class Counter {
    private int count = 0;

    public void increment() {
        count++;
    }
}

This implementation is not thread-safe because multiple threads can access the count field simultaneously and may generate Inconsistent results.

Safe implementation (using synchronized blocks):

public class Counter {
    private int count = 0;

    public void increment() {
        synchronized (this) {
            count++;
        }
    }
}

Use synchronized blocks to mark the increment method as being accessed by only one thread at a time.

Safe implementation (using atomic variables):

import java.util.concurrent.atomic.AtomicInteger;

public class Counter {
    private AtomicInteger count = new AtomicInteger(0);

    public void increment() {
        count.incrementAndGet();
    }
}

AtomicInteger provides an atomic incrementAndGet operation, It increments the counter and returns the updated value in a single step.

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