Java multi-thread programming, knowledge of basic concepts of Java multi-thread programming, thread-safe processing methods, concurrent programming modes, etc., combined with specific code examples to explain

Java is a high-level language that supports multi-threaded programming, which can improve the execution efficiency and responsiveness of programs. In this article, we will introduce the basic concepts of Java multi-threaded programming, thread-safe processing methods, and concurrent programming patterns, etc., and explain it with specific code examples.

First, the basic concept of Java multithreaded programming

1. The concept of thread

A thread is the smallest unit in an operating system that can run independently, and it is also the smallest unit of concurrent program execution. A process can contain multiple threads, and these threads can perform different tasks at the same time.

In Java, threads are implemented through the Thread class. You can create a thread by inheriting the Thread class or implementing the Runnable interface, and then call the start() method to start the thread.

1. thread life cycle

The life cycle of a Java thread includes the following stages:

• New state (New): The thread has been created but not yet started.
• Ready state (Runnable): After the thread is created, it waits for the CPU to schedule execution.
• Running state (Running): The CPU is executing the code in the thread.
• Blocked state (Blocked): The thread is blocked and waits for a certain condition (such as a lock) to be satisfied before entering the ready state again.
• Terminated state (Terminated): The thread is terminated after execution is complete or an exception occurs.

1. Thread Synchronization and Mutex

Thread synchronization and mutual exclusion are very important concepts in multithreaded programming. When multiple threads access shared resources, there will be a problem of resource competition. In order to avoid data inconsistency, it is necessary to perform synchronization and mutual exclusion on shared resources.

Java provides a variety of synchronization and mutual exclusion methods, such as the synchronized keyword, ReentrantLock class, Semaphore class, etc.

Second, the thread-safe processing method

Thread safety means that when multiple threads access shared data, there will be no data inconsistency. Thread-safe processing methods include the following aspects:

1. Use the synchronized keyword

The synchronized keyword can mark a code block as a synchronized code block, and only the thread that has acquired the lock can execute the code block. Using the synchronized keyword can effectively avoid the problem of multiple threads modifying shared data at the same time.

For example, here is an example of using the synchronized keyword to achieve thread safety:

public class Counter {
    private int count;

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

    public synchronized void decrement() {
        count--;
    }

    public int getCount() {
        return count;
    }
}

1. use the volatile keyword

The volatile keyword can ensure that when multiple threads access the same variable, the value of the variable is visible. When a thread modifies the value of this variable,

Other threads can immediately see the latest value of this variable, and all threads see the value of this variable in the same order.

The following is an volatileexample code for a thread-safe counter implemented using keywords:

public class VolatileCounter {
    private volatile int count;

    public int getCount() {
        return count;
    }

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

In this example, the value of the counter is a volatilevariable, which ensures that after any thread modifies the value of the counter, other threads can immediately see the latest value of this value. The method increment()is an atomic operation, which also ensures that updates to the counter value are thread-safe.

It should be noted that volatilethe keyword can only guarantee the thread safety of a single variable, and other thread-safe methods need to be used for the operation of multiple variables, such as synchronized, , Locketc. In addition, volatilekeywords can only guarantee the visibility and order of variables, but cannot guarantee atomicity. Therefore, for some scenarios that require atomic operations, such as accumulation operations, other thread-safe methods need to be used.

In actual programming, it is necessary to select an appropriate thread-safe method according to specific scenarios and requirements to ensure the correctness and performance of the program.

1. Concurrent Programming Patterns

In concurrent programming, some common patterns are used to solve common concurrency problems. These modes include but are not limited to the following:

3.1. Thread pool

Thread pooling is a technique that pre-creates a set of threads. When a task needs to be processed, a thread can be obtained from the pool and assigned to the task, and when the task is completed, the thread is returned to the pool for reuse. The advantage of this approach is that it avoids the overhead of frequent thread creation and destruction, and improves system performance.

Here is a sample code that uses Java's built-in thread pool:

ExecutorService executorService = Executors.newFixedThreadPool(10);

for (int i = 0; i < 100; i++) {
    executorService.submit(new Task(i));
}

executorService.shutdown();

This example creates a thread pool with 10 threads and submits 100 tasks. submit()The method submits the task to the thread pool and returns an Futureobject that can be used to check the execution status and results of the task. After all tasks are executed, shutdown()a method needs to be called to close the thread pool.

3.2. Read-write lock

Read-write lock is an efficient lock mechanism that allows multiple threads to read shared resources at the same time, but only allows one thread to write to shared resources. The implementation of read-write lock can improve the concurrency performance of the system because it reduces unnecessary waiting and competition.

Here is a sample code that uses Java's built-in read-write lock:

ReadWriteLock lock = new ReentrantReadWriteLock();
lock.readLock().lock();
try {
    // 读取共享资源
} finally {
    lock.readLock().unlock();
}

lock.writeLock().lock();
try {
    // 写入共享资源
} finally {
    lock.writeLock().unlock();
}

This example demonstrates how to use Java's built-in read-write locks. First acquire a read lock, then read the shared resource; then acquire a write lock, and then write to the shared resource. The advantage of the read-write lock is that it allows multiple threads to read shared resources at the same time, thereby improving the concurrency performance of the system.

3.3. Signal amount

A semaphore is a synchronization tool used to control concurrent access. It is usually used to limit the number of threads accessing a shared resource at the same time. In Java, Semaphorea semaphore can be implemented using a class.

Here is a sample code that uses Java's built-in semaphores:

Semaphore semaphore = new Semaphore(10);

semaphore.acquire();
try {
    // 访问共享资源
} finally {
    semaphore.release();
}