Program Thread 和 Process的不一樣點

• 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是一個存在disk中且斷電或重啓不會消失可執行文件，存儲在存儲媒介中，以實體文件的形態存在

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.

本文來自 Abbymz 的CSDN 博客 ，全文地址請點擊：https://blog.csdn.net/Abby210/article/details/51225034?utm_source=copy

或者能夠稱之爲persistently 的文件，斷電也不會消失。

What is Process ?

當program被執行以後，就變成了進程。執行者的權限和程序所需的資料都會載入到內存中，OS會給予這些內存單元一個pid。

Unit of resource ownership (allocation) and unit of protection

text， Code of Programmer
Data
Heap
Stack

一個program能夠建立出不少個進程，關機或停電會死掉

Process的組成

• Permission user or kernel
• Priority
• Files
• ID
  • PID
  • PPID
  • Folk
  • UserID
• Protected access to
  • Processors
  • other process
  • Files
  • I/O
• A virtual space that holds the process image

What is Thread ?

線程稱之爲Lightweight Process，一個進程能夠有多個線程，他們共享一片內存

• 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

多線程的好處

• 開啓線程要快於開啓進程
• 關閉線程要快於關閉進程
• 切換線程要快於切換進程
• 線程能夠相互通信

什麼叫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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