与非JIT编译器相比,JIT编译器具体做什么?有人能给出简洁易懂的描述吗?
当前回答
JVM actually performs compilation steps during runtime for performance reasons. This means that Java doesn't have a clean compile-execution separation. It first does a so called static compilation from Java source code to bytecode. Then this bytecode is passed to the JVM for execution. But executing bytecode is slow so the JVM measures how often the bytecode is run and when it detects a "hotspot" of code that's run very frequently it performs dynamic compilation from bytecode to machinecode of the "hotspot" code (hotspot profiler). So effectively today Java programs are run by machinecode execution.
其他回答
JVM actually performs compilation steps during runtime for performance reasons. This means that Java doesn't have a clean compile-execution separation. It first does a so called static compilation from Java source code to bytecode. Then this bytecode is passed to the JVM for execution. But executing bytecode is slow so the JVM measures how often the bytecode is run and when it detects a "hotspot" of code that's run very frequently it performs dynamic compilation from bytecode to machinecode of the "hotspot" code (hotspot profiler). So effectively today Java programs are run by machinecode execution.
JIT指的是一些JVM实现中的执行引擎,它更快,但需要更多内存,是一种即时编译器。在此方案中,方法的字节码在第一次调用方法时被编译为本机机器码。然后缓存该方法的本机机器码,以便下次调用相同的方法时可以重用它。
Just In Time编译器也称为JIT编译器 Java的性能改进。默认启用。它是 编译在执行时完成。 Java通过将JIT编译器包含在 JVM。
即时编译器(JIT)是一种软件,它接收一个不可执行的输入,并返回要执行的适当机器代码。例如:
Intermediate representation JIT Native machine code for the current CPU architecture
Java bytecode ---> machine code
Javascript (run with V8) ---> machine code
其结果是,对于特定的CPU体系结构,必须安装适当的JIT编译器。
区别编译器、解释器和JIT
虽然在一般情况下,当我们想要将源代码转换为机器码时可能会有例外,但我们可以使用:
Compiler: Takes source code and returns a executable Interpreter: Executes the program instruction by instruction. It takes an executable segment of the source code and turns that segment into machine instructions. This process is repeated until all source code is transformed into machine instructions and executed. JIT: Many different implementations of a JIT are possible, however a JIT is usually a combination of a compiler and an interpreter. The JIT first turn intermediary data (e.g. Java bytecode) which it receives into machine language via interpretation. A JIT can often measures when a certain part of the code is executed often and the will compile this part for faster execution.
20%的字节码在80%的时间内被使用。JIT编译器获得这些统计数据,并优化这20%的字节代码,通过添加内联方法、删除未使用的锁等,并创建特定于这台机器的字节码来更快地运行。我引用这篇文章,我发现它很方便。http://java.dzone.com/articles/just-time-compiler-jit-hotspot
推荐文章
- 是否可以动态编译和执行c#代码片段?
- 为什么Java类的编译与空行不同?
- 如何使用cmake创建共享库?
- 在C和c++中静态变量存储在哪里?
- 无法加载文件或程序集…参数不正确
- 如果使用if-return-return或if-else-return?
- Java是编译型编程语言还是解释型编程语言?
- 为什么Swift的编译时间这么慢?
- 选项(RECOMPILE)总是更快;为什么?
- 如何在Angular 2.0中使用/创建动态模板来编译动态组件?
- 如何修复从源代码安装PHP时未发现xml2-config的错误?
- 用自己的语言编写编译器
- 带有返回类型的Java方法在没有返回语句的情况下编译
- 使用g++编译多个.cpp和.h文件
- 在Visual Studio中设置“首选32位”的目的是什么?它实际上是如何工作的?