进程、线程和轻量级进程
- created: 2024-12-26T21:04+08:00
- categories: operating-system
进程是对资源的抽象。
很久以前，Linux 的线程实现有一个弊端1： 当一个线程阻塞时，会阻塞同个进程内的所有其他线程。
Threads are often mixed with the term Light Weight Processes or LWPs. The reason dates back to those times when Linux supported threads at user level only. This means that even a multi-threaded application was viewed by kernel as a single process only. This posed big challenges for the library that managed these user level threads because it had to take care of cases that a thread execution did not hinder if any other thread issued a blocking call.
那进程内部线程的轮换只能完全由用户态控制， 一旦进程的一个线程进入了 kernel 然后被阻塞，这个线程就没法回到 user space 通过调度执行其他线程。
我的理解这样原因是，假设内核对进程的描述叫做 task_struct，它只能看到每个 process 的 task_struct，
多个线程也只是共享一个 task_struct，所以多个线程一次只能有一个代表该进程进入内核。
后来线程的实现改为了 lwp，light weight process，
Later on the implementation changed and processes were attached to each thread so that kernel can take care of them. But, as discussed earlier, Linux kernel does not see them as threads, each thread is viewed as a process inside kernel. These processes are known as light weight processes.
一个进程内的很多线程，可以说是共享很多资源的 light weight process，一个被阻塞以后，不会相互影响了。
1. What are Linux Processes, Threads, Light Weight Processes, and Process State ↩