In-depth analysis of Java's underlying technology: how to implement thread scheduling and lock optimization

In-depth analysis of Java's underlying technology: How to implement thread scheduling and lock optimization

Introduction:
In Java development, it involves the concurrent execution of threads and shared resources Access, thread scheduling and lock optimization are essential core technologies. This article will analyze how to implement thread scheduling and lock optimization in Java from a low-level perspective, and give specific code examples.

1. Thread Scheduling

1. The concept of thread scheduling
   Thread scheduling refers to the process by which the operating system allocates CPU execution time to multiple threads. Thread scheduling in Java is completed by the JVM and the operating system. The JVM will map Java threads to operating system threads and allocate CPU time to different threads according to certain strategies.
2. Thread Scheduling Strategy
   In Java, thread scheduling adopts a preemptive strategy, that is, threads with high priority get CPU execution time first. The thread priority here is an operating system level concept. The thread priority in Java generally corresponds to the thread priority of the operating system one-to-one.

The priority of a thread in Java is controlled by the setPriority() and getPriority() methods provided by the Thread class. The priority of threads is divided into levels 1~10, with level 1 being the lowest priority and level 10 being the highest priority. You can set the thread's priority through setPriority(), and getPriority() is used to get the thread's priority.

The JVM will allocate CPU time according to the priority of the thread, but there is no guarantee that a thread with a high priority will execute faster than a thread with a low priority. Because the specific scheduling situation is also affected by the operating system.

3. Thread Scheduling Example
   The following example shows how to set the priority of a thread and get the priority of a thread:

public class ThreadPriorityExample {
   public static void main(String[] args) {
      Thread t1 = new MyThread();
      Thread t2 = new MyThread();
      
      t1.setPriority(Thread.MIN_PRIORITY);
      t2.setPriority(Thread.MAX_PRIORITY);
      
      t1.start();
      t2.start();
   }
   
   static class MyThread extends Thread {
      @Override
      public void run() {
         System.out.println("线程优先级：" + getPriority());
      }
   }
}

In the above example, we create Two threads are named t1 and t2, and different priorities are set respectively. Then after starting the thread, obtain the priority of the thread through the getPriority() method and output it.

2. Lock optimization

1. The concept of lock
   Locks in Java are used to protect access to shared resources and prevent data inconsistency caused by multiple threads modifying shared resources at the same time. . Common locks include the synchronized keyword and Lock interface.
2. Classification of locks
3. Biased lock: When the lock has been accessed by the same thread, the JVM will think that the lock is biased towards the current thread, and thus mark the lock as a biased lock. The purpose of biased locking is to reduce the time to acquire the lock and improve the performance of the program.
4. Lightweight lock: When the lock is alternately accessed by multiple threads, the JVM will mark the lock as a lightweight lock. The purpose of lightweight locks is to reduce competition between threads and improve concurrency performance.
5. Heavyweight lock: When multiple threads access the lock at the same time, the JVM will mark the lock as a heavyweight lock. Heavyweight locks are implemented through object monitors, ensuring that only one thread can obtain the lock at the same time.
6. Lock optimization example
   The following example shows how to use the synchronized keyword for lock optimization:

public class LockOptimizationExample {
   private static int count = 0;
   private static final Object lock = new Object();

   public static void main(String[] args) {
      for (int i = 0; i < 10; i++) {
         new Thread(() -> {
            synchronized (lock) {
               count++;
               System.out.println("当前值：" + count);
            }
         }).start();
      }
   }
}

In the above example, we use the synchronized keyword to increase count Lock ensures the atomic operation of count in a multi-threaded environment. By locking with the synchronized keyword, we can avoid the problem of data inconsistency caused by multiple threads modifying count at the same time.

Conclusion:
This article introduces the related concepts of thread scheduling and lock optimization in Java, as well as specific code examples. Thread scheduling and lock optimization are indispensable core technologies in Java development. Understanding and mastering these technologies is very important to improve program concurrency performance and ensure data consistency. I hope this article will be helpful to readers in the underlying Java technology.

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