Operating Systems 2017F Lecture 19

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[Notes]

Sample sample


Additional Notes

Where's main?

  • lots of program shave "main" functions - a function that runs first and controls the execution of the program
  • Do these have "main" functions?
    • Linux kernel modules
    • FUSE applications?
    • the linux kernel?
    • node web applications?


In many systems, "main" just sets up even handlers

  • the event loop can be implicit or explicit
    • or there may be no loop at all, just handlers and "interrupts" some kind
  • event loops poll (check) to see when there are new events
  • what are event loops for node app?
    • where are interrupts for node apps?
      • Incoming network requests, it's an event

Code run differently in the kernel :

1)functions runs on the bhealf of insmod, unles sit is Independence context

2)codes that run on the bhelaf o the process


3)after an interrupt: no process , it is an interrupt cotext

4) file names : regular programs but the square brackets, execution context + address space. they share the kernel's address space, they are called kernel threads which are independently scheduling . You can not kill them but you can change their scheduling , maybe their priority but not 100%.

does it create a proces? no , but it can create a kernel thread (is it a process? virtual adress space, .
multi- threaded: maintains multiple address processes , ex: fire fox.

ps -elF | less "number" : displays threads.

top : displays all the processes

ls time : shows you the time .

sys: how much time in the kernel space real: how much time user : how much time in user space

process : can't manipulate its own memory map directly, it has an address space, but cant change it. Process: is limited but the kernel is not and the kernel can change it's own address and in charge of its self.

Kernel tasks : are threads, when a process makes a system call , thi sis schedules in the process priority.



OS kernels are essentially the same thing