How to implement JVM memory model and GC tuning of Java underlying technology

How to implement the JVM memory model and GC tuning of Java's underlying technology

Introduction:
As a widely used programming language, Java's underlying technology is It is crucial for developers. Among them, the JVM's memory model and GC tuning are very critical parts. This article will introduce the relevant knowledge of JVM memory model and GC tuning in detail, with specific code examples.

1. JVM memory model
The JVM memory model is the memory layout used by the Java Virtual Machine (JVM) during runtime. It consists of multiple parts such as program counter, virtual machine stack, local method stack, heap and method area.

1. Program Counter
   The program counter is a small memory space that is used to store the address of the next instruction to be executed. In a multi-threaded environment, each thread has its own independent program counter.
2. Virtual machine stack (JVM Stack)
   The virtual machine stack is used to store the stack frame of the method. When each thread executes a method, a stack frame will be created. After the method is executed, the stack frame will be be destroyed. The stack frame includes local variable table, operand stack, dynamic link, method exit and other information.
3. Native Method Stack
   The local method stack is similar to the virtual machine stack, except that the local method stack serves local methods. When the virtual machine calls a local method, the corresponding local method stack will be called.
4. Heap
   The heap is the largest piece of memory in the JVM, used to store object instances and arrays. It is an area shared by threads. The heap can be garbage collected through the garbage collector.
5. Method Area (Method Area)
   The method area is used to store loaded class information, constants, static variables, code compiled by the just-in-time compiler and other data. It is also an area shared by threads.

2. GC Tuning
GC (Garbage Collection) is a part of memory management in Java. It is responsible for recycling objects that are no longer used to release memory space. GC tuning can improve program performance.

1. Garbage collection algorithm
   Java has a variety of garbage collection algorithms, such as mark-clear, copy, mark-compression, etc. The garbage collection algorithm can be adjusted by setting JVM command line parameters.
2. Garbage Collector
   JVM has multiple built-in garbage collectors, such as Serial, Parallel, CMS, G1, etc. Different garbage collectors are suitable for different scenarios, and you can choose the appropriate garbage collector according to specific needs.
3. Memory parameter tuning
   You can optimize GC performance by adjusting the memory parameters of the JVM. For example, the -Xmx parameter can set the maximum available memory of the heap, and the -Xms parameter can set the initial size of the heap.

Sample code:
The following is a simple sample code that demonstrates how to optimize GC performance by adjusting the memory parameters of the JVM and selecting an appropriate garbage collector.

public class GCExample {
    public static void main(String[] args) {
        // 设置堆的最大可用内存为512MB
        //-Xmx512m
        // 设置堆的初始大小为256MB
        //-Xms256m

        // 执行一些耗时操作

        // 创建大对象，占用较多内存
        byte[] bigObject = new byte[100 * 1024 * 1024];

        // 执行一些其他操作

        // 手动调用垃圾回收
        System.gc();
    }
}

Conclusion:
This article introduces the relevant knowledge of JVM memory model and GC tuning of Java's underlying technology. By understanding the JVM memory model and the principles of GC tuning, and using sample code to demonstrate how to optimize GC performance. By properly adjusting the memory parameters of the JVM and selecting an appropriate garbage collector, the performance of Java programs can be improved. I hope this article will be helpful to Java developers in their learning and practice of underlying technologies.

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