January 2021
Intermediate to advanced
342 pages
9h 1m
Chinese
Content preview from Java性能优化实践：JVM调优策略、工具与技巧
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182
｜
第
10
章
•
可能要向调用者返回一个结果。
内联是
JIT
编译器所应用的最重要的优化之一，也叫
网关优化
（
gateway optimization
）， 因
为它通过消除方法的边界，缩短了相关代码的距离。
考虑如下代码：
int
result = add(a, b);
private
int
add(
int
x,
int
y) {
return
x + y;
}
内联优化会将
add()
的方法体复制到它的调用点中，实际上得到：
int
result = a + b;
HotSpot
的内联编译器优化支持开发人员编写组织清晰、可复用的代码。它代表的理念是，
开发人员不需要手动进行细微的优化。相反，
HotSpot
使用自动化的统计分析来确定相关
代码何时应该放在一起。内联也进而拓宽了其他优化的范围，包括：
•
逃逸分析（
escape analysis
）
•
死代码消除（
dead code elimination
，
DCE
）
•
循环展开（
loop unrolling
）
•
锁消除（
lock elision
）
10.3.1
内联的限制
有时虚拟机需要对内联子系统施加一些限制。比如，虚拟机可能需要控制：
• JIT
编译器优化一个方法所花的时间；
•
生成的原生代码的大小（这会进而影响代码缓存所占用的内存多少）。
如果没有这些约束，编译器可能就会陷入很深的内联调用链中不能自拔，或是会因巨大
的原生方法而填满代码缓存。
JIT
编译资源非常宝贵，这个一般性原则在这里再次发挥
作用。
HotSpot
在决定是否内联某个方法时会考虑几个因素，包括： ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.