- Thread is for execution
- Kernel level thread,physical parallelism
- Cores Divide work amount of physical cores / CPU
- Load balancing
- Data Splitting
- Which will lead to data dependency coodination and message passing
- Bad thing for multiple cores is this is hard for Testing and debugging
- User level thread only have logical parallelism
- Example,Read from user input is blocking; we have to work on it to make it logical parallelism
- Process is for resource
What is Program
Program是一个存在disk中且断电或重启不会消失可执行文件，存储在存储媒介中，以实体文件的形态存在
A program is an executable file residing on the disk (secondary storage) in a directory. It is also termed as a set of instructions stored in the secondary storage device that are intended to carry out a specific job. It is read into the primary memory and executed by the kernel.
本文来自 Abbymz 的CSDN 博客 ，全文地址请点击：https://blog.csdn.net/Abby210/article/details/51225034?utm_source=copy
或者可以称之为persistently 的文件，断电也不会消失。
What is Process ?
当program被执行之后，就变成了进程。执行者的权限和程序所需的资料都会载入到内存中，OS会给予这些内存单元一个pid。
Unit of resource ownership (allocation) and unit of protection
一个program可以创建出很多个进程，关机或停电会死掉
Process的组成
- Permission user or kernel
- Priority
- Files
- ID
- Protected access to
- Processors
- other process
- Files
- I/O
- A virtual space that holds the process image
What is Thread ?
线程称之为Lightweight Process，一个进程可以有多个线程，他们共享一片内存
- has access to the same data
- When one thread alters a data,other threads see the results
- When one thread open a file,other threads can also access that file.
Unit of dispatch or unit of execution
多线程的好处
- 开启线程要快于开启进程
- 关闭线程要快于关闭进程
- 切换线程要快于切换进程
- 线程可以相互通讯
什么叫Multithreading
The ability of an OS to support multiple,concurrent paths of execution within a single process.
Process and thread states
- Ready
- new process usually set as read state
- At this time scheduler is not pick it up yet.
- If it get picked by scheduler and running in CPU,then goes to Running State
- If it get external event,something like lock,then goes to block
- Running,
- Scheduler picked it up,and CPU is run this instruction
- If it get finished,goes to Exit states
- If it get IO interrupts,goes to ready,blocked status
- If it can not get the resource which is conflict with other process,goes to deadlock
- Block
- If it lock (wait able ) is release,or IO is completed,then goes to Ready
- Deadlock
- Exit (Zombie State)
- When process is finished,waiting for cleaning up
How Deadlock happen ?
- When process A has resource a,and it need resource b from process B.
- At the same time,process B need resource a from A
- Then those process gonna have deadlock due to both of them can get the resource they need.
Reference
https://slideplayer.com/slide/5219996/
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