Home 类库下载 java类库 jvm memory area

jvm memory area

Nov 05, 2016 pm 04:34 PM
java

Memory area

Program counter

This is similar to the function of the program counter in the processor. It records the address of the next bytecode

But the program counter of the processor serves the process, in jvm The program counter serves threads

So the program counter of jvm is private to the thread. The declaration period is the same as the thread. The program counters between threads do not interfere with each other

Because it records the address of the next bytecode, so it is wrong Native method service in java. The native method will directly start a process, which is controlled by the program counter in the CPU. The program counter is the only area in the jvm that will not throw OutOfmemoryError. The virtual machine stack is also the same as this. The function of the stack in the CPU is similar. When entering a method, a stack frame is pushed into the stack. The stack frame records the local variable table, operand stack, dynamic link, and method exit. When exiting this method, pop the current stack frame

The virtual machine stack is thread-private because it is oriented to method services


Local variable table


The local variable table records the local variables in the method Type (such as int, boolean, char,..., reference type) and the memory address of this variable


operand stack

operand stack is equivalent to the general register in the cpu, which stores the logical operation unit Processed values, many instructions need to read values ​​from this area (add, cmp, mov,...)



Method exit

Here is recorded the next instruction executed after processing the current method Address


Native method stack


The local method stack is actually similar to the virtual machine stack, except that it serves native methods. The virtual machine stack only serves bytecode


heap

This area is Where most subjects live. Naturally, it is also the focus of the garbage collector.

This area is responsible for storing instances of objects, and the memory space of the objects is allocated here. Because most objects live here, it is an area shared by all threads.

The heap is also subdivided into the new generation area and the old generation area. The main survivors in the new generation area are objects that "live and die". They are born frequently and destroyed frequently. This is an area that is targeted by garbage collectors. The survival of the old generation area requires stable objects, so the garbage collector rarely visits here.


The vast majority of objects have short survival times and live in the new generation. Therefore, the Cenozoic area is usually larger than the Old Era area.


Method area

The method area records the information of loaded classes. Such as fully qualified names (package name + class name), methods, fields, descriptors, parameters, constants, and static variables. This area is also shared by all threads.

This area also has a name - the Eternal Era, which means that this area is rarely cleared. Because the cleanup range of a class is very small, and the requirements for determining whether a class is no longer needed are more demanding, the garbage collector rarely cleans this area.


Runtime constant pool


This area records literal and symbol references generated during compilation. It is also shared by all threads.


Literal

Literal includes strings marked by double quotes "", as well as some basic data types hard-coded in the code, these are all constants.


In jdk1.6, the runtime constant pool is part of the method area. When a constant is found, first check whether the constant is already stored in the runtime constant pool. If not, copy a copy to the runtime constant pool. Every subsequent attempt to create a constant with the same value directly references the runtime constant pool.


Starting from jdk1.7, the runtime constant pool has been divided into the heap. For the first occurrence of a constant, it is no longer copied to the runtime constant pool, but a reference is retained in the runtime constant pool, pointing to the memory address where the constant appears for the first time.


Direct memory

This area is actually not part of the jvm, but belongs to other processes. When a native method is called, a direct memory may be generated.

Direct memory refers to the memory space used in the native method. For example, NIO operations use native methods to read and write files. At this time, a direct memory pointing to the memory (cache) for reading and writing files will be generated.


Note that the direct memory is not in the jvm, but a reference will be maintained in the jvm heap, pointing to the direct memory of the memory space. This avoids frequent copying of data back and forth from the memory space and Java heap in operations similar to NIO.

Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

Video Face Swap

Video Face Swap

Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

Java Spring Interview Questions Java Spring Interview Questions Aug 30, 2024 pm 04:29 PM

In this article, we have kept the most asked Java Spring Interview Questions with their detailed answers. So that you can crack the interview.

Break or return from Java 8 stream forEach? Break or return from Java 8 stream forEach? Feb 07, 2025 pm 12:09 PM

Java 8 introduces the Stream API, providing a powerful and expressive way to process data collections. However, a common question when using Stream is: How to break or return from a forEach operation? Traditional loops allow for early interruption or return, but Stream's forEach method does not directly support this method. This article will explain the reasons and explore alternative methods for implementing premature termination in Stream processing systems. Further reading: Java Stream API improvements Understand Stream forEach The forEach method is a terminal operation that performs one operation on each element in the Stream. Its design intention is

PHP: A Key Language for Web Development PHP: A Key Language for Web Development Apr 13, 2025 am 12:08 AM

PHP is a scripting language widely used on the server side, especially suitable for web development. 1.PHP can embed HTML, process HTTP requests and responses, and supports a variety of databases. 2.PHP is used to generate dynamic web content, process form data, access databases, etc., with strong community support and open source resources. 3. PHP is an interpreted language, and the execution process includes lexical analysis, grammatical analysis, compilation and execution. 4.PHP can be combined with MySQL for advanced applications such as user registration systems. 5. When debugging PHP, you can use functions such as error_reporting() and var_dump(). 6. Optimize PHP code to use caching mechanisms, optimize database queries and use built-in functions. 7

PHP vs. Python: Understanding the Differences PHP vs. Python: Understanding the Differences Apr 11, 2025 am 12:15 AM

PHP and Python each have their own advantages, and the choice should be based on project requirements. 1.PHP is suitable for web development, with simple syntax and high execution efficiency. 2. Python is suitable for data science and machine learning, with concise syntax and rich libraries.

Java Program to Find the Volume of Capsule Java Program to Find the Volume of Capsule Feb 07, 2025 am 11:37 AM

Capsules are three-dimensional geometric figures, composed of a cylinder and a hemisphere at both ends. The volume of the capsule can be calculated by adding the volume of the cylinder and the volume of the hemisphere at both ends. This tutorial will discuss how to calculate the volume of a given capsule in Java using different methods. Capsule volume formula The formula for capsule volume is as follows: Capsule volume = Cylindrical volume Volume Two hemisphere volume in, r: The radius of the hemisphere. h: The height of the cylinder (excluding the hemisphere). Example 1 enter Radius = 5 units Height = 10 units Output Volume = 1570.8 cubic units explain Calculate volume using formula: Volume = π × r2 × h (4

PHP vs. Python: Core Features and Functionality PHP vs. Python: Core Features and Functionality Apr 13, 2025 am 12:16 AM

PHP and Python each have their own advantages and are suitable for different scenarios. 1.PHP is suitable for web development and provides built-in web servers and rich function libraries. 2. Python is suitable for data science and machine learning, with concise syntax and a powerful standard library. When choosing, it should be decided based on project requirements.

PHP vs. Other Languages: A Comparison PHP vs. Other Languages: A Comparison Apr 13, 2025 am 12:19 AM

PHP is suitable for web development, especially in rapid development and processing dynamic content, but is not good at data science and enterprise-level applications. Compared with Python, PHP has more advantages in web development, but is not as good as Python in the field of data science; compared with Java, PHP performs worse in enterprise-level applications, but is more flexible in web development; compared with JavaScript, PHP is more concise in back-end development, but is not as good as JavaScript in front-end development.

Create the Future: Java Programming for Absolute Beginners Create the Future: Java Programming for Absolute Beginners Oct 13, 2024 pm 01:32 PM

Java is a popular programming language that can be learned by both beginners and experienced developers. This tutorial starts with basic concepts and progresses through advanced topics. After installing the Java Development Kit, you can practice programming by creating a simple "Hello, World!" program. After you understand the code, use the command prompt to compile and run the program, and "Hello, World!" will be output on the console. Learning Java starts your programming journey, and as your mastery deepens, you can create more complex applications.

See all articles