Java

• Java 第1篇 https://www.iteye.com/blog/lobin-2326332

• Java 第2篇: 哈希表 https://lobin.iteye.com/admin/blogs/2326558

• Java 第3篇: 集合 https://www.iteye.com/blog/lobin-2326327

• Java 第4篇: 线程 https://lobin.iteye.com/admin/blogs/2327713

• Java: 高级编程 https://www.iteye.com/blog/lobin-2431622

• Java: 函数式编程 https://www.iteye.com/blog/lobin-2434203

• Java: 网络编程 https://www.iteye.com/blog/lobin-2326354

 

内存模型

任何编程语言都有它的内存模型。不管什么编程语言都定义了程序在运行时对内存的访问方式。CPU处理器在执行指令时，如果需要访问内存，比如操作某个变量，也涉及到对内存的访问方式。

 

Java内存模型、C/C++内存模型和多处理器CPU内存模型关系

 

可见性

内存可见性

T：a--->b--->c--->d--->...--->

 

                      T

             +----------------+

              |    处理器    | 

             +----------------+

             +----------------+

              |     cache   |

             +----------------+

             +----------------+

              |     内存      |

             +----------------+

 

Java内存模型和多处理器CPU内存模型关系

 

Java内存模型：

参考另一篇文章：https://lobin.iteye.com/blog/2325729

 

C/C++内存模型：

https://en.cppreference.com/w/c/language/memory_model

https://en.cppreference.com/w/cpp/language/memory_model

 

内存管理

 

Java GC机制

分代回收的GC机制

 

Java Reachability

Automatically-cleared references

Soft and weak references are automatically cleared by the collector before being added to the queues with which they are registered, if any. Therefore soft and weak references need not be registered with a queue in order to be useful, while phantom references do. An object that is reachable via phantom references will remain so until all such references are cleared or themselves become unreachable. 

Reachability

Going from strongest to weakest, the different levels of reachability reflect the life cycle of an object. They are operationally defined as follows:

• An object is strongly reachable if it can be reached by some thread without traversing any reference objects. A newly-created object is strongly reachable by the thread that created it.
• An object is softly reachable if it is not strongly reachable but can be reached by traversing a soft reference.
• An object is weakly reachable if it is neither strongly nor softly reachable but can be reached by traversing a weak reference. When the weak references to a weakly-reachable object are cleared, the object becomes eligible for finalization.
• An object is phantom reachable if it is neither strongly, softly, nor weakly reachable, it has been finalized, and some phantom reference refers to it.
• Finally, an object is unreachable, and therefore eligible for reclamation, when it is not reachable in any of the above ways. 

 

GC

 

 

年轻代

 

年老代

 

持久代

 

 

GC算法

 

JVM

 

# ldd java

linux-gate.so.1 =>  (0x00eea000)

libpthread.so.0 => /lib/libpthread.so.0 (0x00c89000)

libjli.so => /usr/local/jdk1.8.0_261/bin/./../lib/i386/jli/libjli.so (0x00a89000)

libdl.so.2 => /lib/libdl.so.2 (0x00621000)

libc.so.6 => /lib/libc.so.6 (0x00653000)

/lib/ld-linux.so.2 (0x800a7000)

 

# ldd javac

linux-gate.so.1 =>  (0x0094a000)

libpthread.so.0 => /lib/libpthread.so.0 (0x00db8000)

libjli.so => /usr/local/jdk1.8.0_261/bin/./../lib/i386/jli/libjli.so (0x0054a000)

libdl.so.2 => /lib/libdl.so.2 (0x006f5000)

libc.so.6 => /lib/libc.so.6 (0x00168000)

/lib/ld-linux.so.2 (0x800d3000)

 

参考文章：https://lobin.iteye.com/blog/617507