Modern Operating Systems 笔记 - Deadlocks

操作系统 算法 死锁

Resources

A preemptable resource is one that can be taken away from the process owning it with no ill effects.

A nonpreemptable resource is one that cannot be taken away from its current owner without causing the computation to fail.

Resource Acquisition

  1. Request the resource.
  2. Use the resource.
  3. Release the resource.

A possible implementation:

  1. down on the semaphore to aquire the resource.
  2. using the resource.
  3. up on the semaphore to release the resource.

Modern Operating Systems 笔记 - Interprocess Communication

操作系统 IPC 中断 互斥量 信号量

race conditions

Two or more processes are reading or writing some shared data and the final result depends on who runs precisely when.

Critical Regions

mutual exclusion

Prohibit more than one process from reading and writing the shared data at the same time.

critical region

Also called critical section , the part of the program where the shared memory is accessed.

Conditions to a good solution

  1. No two processes may be simultaneously inside their critical regions
  2. No assumptions may be made about speeds or the number of CPUs
  3. No process running outside its critical region may block other processes
  4. No process should have to wait forever to enter its critical region

Modern Operating Systems 笔记 - Threads

fork pthread sed 线程 内核空间 操作系统 用户空间 进程

Thread Usage

  1. Multiple activities going on at once with the ability to share an address space
  2. Lighter weight than processes, easy to create and destroy.
  3. Overlap activities with substantial I/O to speeding up the application.
  4. Useful on systems with multiple CPUs.

Three ways to construct a server

  1. Thread. Parallelism, blocking system calls.
  2. Single-threaded process. No parallelism, blocking system calls.
  3. Finite-state machine. Parallelism, nonblocking system calles, use interrupts to simulate thread.

Classical Thread Model

Processes are used to group resources together; threads are the entities scheduled for execution on the CPU. There are no protection betwwen threads because (1) it’s impossible, and (2) it should not be nessessary.

While threads share one memory space, it takes fewer space to maintain a thread, including Program Counter, Registers, Stack and State.

Modern Operating Systems 笔记 - Processes

操作系统 进程 Unix Windows fork kill sed

pseudoparallelism

The illusion of parallelism while CPU is switching from process to process quickly.

The Process Model

process is an instance of an executing program, is the activity of a program.

If a program is running twice, it counts as two processes.

Process Creation

Processes are created when

  1. System init
  2. Process creation system call by a running process
  3. A user request to create a new process.
  4. Init of a batch job.

Modern Operating Systems 笔记 - Introduction

Unix Windows 操作系统

What is OS

  1. extendes machines : providing programmers(and programs) a clean abstract set of resources instead of the messy hardware
  2. resource manager : managing hardware resources

History of OS

The first digital computer was designed by Charles Babbage. Ada Lovelace was the first programmer(hired by Babbage).

1st Generation Vacuum Tubes

  • The first functioning digital computer, by John Atanasoff and Clifford Berry, Iowa State University.
  • Z3, Konrad Zuse, Berlin.
  • Colossus, a group at Bletchey Park, England
  • Mark I, Howard Aiken, Harvard
  • ENIAC, William Mauchley and J. Presper Eckert, University of Pennsylvania

Vim初级:配置和使用

Vim-Practice Bash Unix Vim sed 编译

Vim是从vi发展出来的一个文本编辑器。代码补全、编译及错误跳转等方便编程的功能特别丰富,在程序员中被广泛使用。和Emacs并列成为类Unix系统用户最喜欢的编辑器。

文档参见:http://vimdoc.sourceforge.net/htmldoc/

中文文档:http://vimcdoc.sourceforge.net/doc/

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