Program vs Process vs Thread

Program

the code stored on your computer disk or non-volatile memory to fulfill a certain task. Including System Programs and Application Programs.

• Program will be compiled or programmed to binary in memory before executing it.

Process

An instance of program that has been loaded into memory along with all the resources needed to operate. A unit for resource allocation

• The Operating System handles the task managing the resources needed to turn program into processes.
• Resources includes:
  • register: some part of CPU to store binary
  • program counter: special register in CPU to do counter work
  • stack: data structure to store local and small things in memory, managed automatically.
  • heap: data structure to store global and big things in memory, managed manually or by Garbage Collection.
• Features:
  • One program may be associated with many processes.
  • Independent Memory Address Space.
  • Inter-communication is expensive.
  • Robust: One failed won't cause another to fail.

Thread

A unit of execution within a process. One process can have one up to many threads. A unit to be scheduled and executed by OS

• Features:
  • Share the same heap in a process
  • Share the same code in a process
  • Has independent registers
  • Has independent stacks
  • Inter-communication is less expensive
  • Vulnerable: one fail can cause another to fail in the same process.

Summary

• The program starts out as a text file of programming code.
• The program is compiled or interpreted into binary form.
• The program is loaded into memory.
• The program becomes one or more running processes.
• Processes are typically independent of each other
• While threads exists as the subset of a process
• Threads can talk with each other more easily than processes can
• Threads are vulnerable to problems caused by other threads in the same process.

💡 对操作系统来说，线程是最小的执行单元，进程是最小的资源管理单元。

Tricks

Reference

• Stack and Heap
• Language C
• 进程线程协程
• 漫画: 什么是协程?