Operating System-Class 6-Feb. 11th

Last time: UNIX/Linux, Windows, and XINU

√ - provide system service to processes

√  - are implemented by a special instruction(“ta” for Sparc) itself in user code, but causes execution to transfer into kernel to run, and when done, return to next user instruction

√ - can be called from a C program via an “envelope function” in C library

o   Sec 2: syscalls (open, close, …)

o   Sec 3: portable standard C library (fopen, fclose, …)

√ - are not portable: fork + exec in UNIX <----> CreateProcess(…) in Windows

 

normal case(eg. %date)

 

 

 

 

no-wait case(eg. %date&)

 

 

 

 

 

XINU: everything is in one address space

-          multiple user processes: can just call the kernel syscall for

-          kernel code

Xinu processes are like UNIX threads

-          share data vars (external C vars)


Xinu: each process has its own stack, so local variables are private to a process (as are local variables in threads).

 


Comer P5: ex1.c

putc(CONSOLE, ‘h’);

-          CONSOLE: dev, standard output for whole system(single user)

-          need: #include <stdio.h>

o   #define CONSOLE 100

-          Note: replace “conf.h” with “stdio.h” in Chapter1 programs (user-level program)

 

To run ex1.c:

1.       build it into Xinu using cross-compiler/loader

-          ex1.lnx <-- file on UNIX system

o   compilation of ex1.c to ex1.opc(object file) which has undefined symbol “putc”

o   cross-loader: combines ex1.opc with Xinu library(*.opc, putc implementation code) & a small C library(*.opc, printf in here, calls putc)

§  static load: no DLLs, all codes needed is in executable

o   output ex1.lnx: contains main, putc code, Xinu core system

2.       Download ex1.lnx into online SAPC, and run it.

 

Comer P8: ex2.c

create(prA, 2000, 20, “proc 1”, 0)

-          create a process in suspended state

-          return pid

o   2000: stack size  (NOTE: never use 200 here, it’s too small: change the book examples)

o   20: priority

o   0: no args

-          resume(pid)

o   put suspended pid into runnable state

 

Semaphores: exist to coordinate concurrent threads/processes

-          can be used for mutex (mutual exclusion)

o   if a resource can be used by only one thread at a time(eg. data structure in memory)

§  we need mutex to guard the resource

·         need API

·         if some other thread is using, then wait

§  Ex.