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CSE451 Section 3

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Reminders Start project 2!

It’s long Read the assignment carefully Read it again

Project 2 will be done in groups of 3

Today: Form project 2 groups Project 2 intro CVS

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Project 2 You have to:

Implement a user thread library Implement synchronization primitives Solve a synchronization problem Add Preemption Implement a multithreaded web server Get some results and write a (small) report

Part a due: in two weeks (Thurs, April 28 12:00pm)

Part b due: 11 days after part a (Monday, May 9 12:00pm)

Part a

Part b

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Simplethreads We give you:

Skeleton functions for thread interface Machine-specific code

Support for creating new stacks Support for saving regs/switching stacks

A generic queue When do you need one?

Very simple test programs You should write more

Singlethreaded web server

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Simplethreads Code Structure

include/sthread.h

Other apps

Web server (web/sioux.c)

test/*.c

lib/sthread_user.h

lib/sthread_user.c

lib/sthread_ctx.c

lib/sthread_ctx.h

You write this

sthread_switch_i386.h

sthread_switch_powerpc.h

lib/sthread_switch.S

lib/sthread_queue.c

lib/sthread_queue.h lib/

sthread_preempt.c

lib/sthread_preempt.h

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Thread Operations void sthread_init()

Initialize the whole system sthread_t sthread_create(func start_func, void

*arg) Create a new thread and make it runnable

void sthread_yield() Give up the CPU

void sthread_exit(void *ret) Exit current thread

What about the TCB?struct _thread {

sthread_ctx_t *saved_ctx; ………

} Others?

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Sample multithreaded program

int main(int argc, char **argv) {int i;

sthread_init(); if (sthread_create(thread_start, (void*)i) == NULL) { printf("sthread_create failed\n"); exit(1);}

sthread_yield(); //yield main thread to our new thread printf("back in main\n"); return 0;}

void *thread_start(void *arg) { printf("In thread_start, arg = %d\n", (int)arg); return 0;}

Output? (assume no preemption)

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Managing Contexts (given) Thread context = thread stack + stack

pointer sthread_new_ctx(func_to_run)

gives a new thread context that can be switched to

sthread_free_ctx(some_old_ctx) Deletes the supplied context

sthread_switch(oldctx, newctx) Puts current context into oldctx Takes newctx and makes it current

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How sthread_switch worksXsthread_switch:

pusha

movl %esp,(%eax)

movl %edx,%esp

popa

ret

Thread 1 TCB … SP

Thread 2 TCB … SP

ESP

CPU

Thread 1 running Thread 2 ready

Want to switch to thread 2…

Thread 2registers

Thread 1 regs

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Push old contextXsthread_switch:

pusha

movl %esp,(%eax)

movl %edx,%esp

popa

ret

Thread 1 TCB … SP

Thread 2 TCB … SP

ESP

CPU

Thread 1 running Thread 2 ready

Thread 2registers

Thread 1registers

Thread 1 regs

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Save old stack pointerXsthread_switch:

pusha

movl %esp,(%eax)

movl %edx,%esp

popa

ret

Thread 1 TCB … SP

Thread 2 TCB … SP

ESP

CPU

Thread 1 running Thread 2 ready

Thread 2registers

Thread 1registers

Thread 1 regs

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Change stack pointersXsthread_switch:

pusha

movl %esp,(%eax)

movl %edx,%esp

popa

ret

Thread 1 TCB … SP

Thread 2 TCB … SP

ESP

CPU

Thread 1 ready Thread 2 running

Thread 2registers

Thread 1registers

Thread 1 regs

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Pop off new contextXsthread_switch:

pusha

movl %esp,(%eax)

movl %edx,%esp

popa

ret

Thread 1 TCB … SP

Thread 2 TCB … SP

ESP

CPU

Thread 1 ready Thread 2 running

Thread 1registers

Thread 2 regs

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Done; returnXsthread_switch:

pusha

movl %esp,(%eax)

movl %edx,%esp

popa

ret

Thread 1 TCB … SP

Thread 2 TCB … SP

ESP

CPU

Thread 1 ready Thread 2 running

Thread 1registers What got switched?

SP PC (how?) Other registers

Thread 2 regs

Adjusting the PCThread 1 TCB … SP

Thread 2 TCB … SP

ESP

CPU

Thread 2 running:switch(t2,...);

0x800: printf(“test 2”);

Thread 1registers

ret pops off the new return address!

ra=0x800

PC

Thread 1 (stopped):switch(t1,t2);

0x400: printf(“test 1”);

ra=0x400

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Things to think about Who will call sthread_switch? Where does sthread_switch return? How do we delete a thread?

Can a thread free its stack itself? Starting up a thread

When you create a new stack with sthread_new_ctx(), you initialize it to run some function foo

sthread_new_ctx doesn’t pass parameters to foo But in sthread_create, you give a function and an

arg! Bottom line: how do you pass arguments to a

function with no arguments?

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Preemption Initially, you will build a non-preemptive

thread library. In part 4, you add preemption

Much more realistic model We give you:

1. Timer interrupts2. Primitives to enable/disable interrupts3. atomic_test_and_set/atomic_clear for

synchronization You must:

Do something on each timer interrupt. (What?) Synchronize all of your code using 2 and 3 above.

More on this later…

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Last note You can compare your

implementation against pthreads (which is preemptive kernel-threads). ./configure --with-pthreads

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What is CVS Version control system for source files Multiple users can work on the same

file simultaneously

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Why use CVS The other way:

Keep every version of code, all with different names: Project2good Project2_10_13_04 Project2working Project2_Feb_2_alex Project2_old

Send emails back and forth with new changes Merge different versions by hand

The CVS way: One version, saved in the CVS repository Multiple people can work on the same file

concurrently CVS merges the edited versions automatically as

you put them back in the repository

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Setting up CVS Set up CVS root environment var

Tells CVS where to find your repository setenv CVSROOT /cse451/yourgroup/cvs (bash) export CVSROOT=/cse451/yourgroup/cvs

Initialize a repository (only one person per group) Create a dir in your group’s dir to hold

repository (master copy of code) cd /cse451/yourgroup mkdir cvs

Initialize repository cvs init

You now have an empty repository

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Setting up CVS (2) Add/Import the simplethreads

distribution to your repository tar xvfz simplethreads-1.20.tar.gz cd simplethreads-1.20 cvs import –m “initial code” simplethreads SIMPLETHREADS SIMPLETHREADS_1_20

cd .. rm –fr simplethreads-1.20

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CVS Commands Check out a project (sandbox, or local copy) to

your home directory to work on: CVS creates a dir simplethreads/ and puts copy of all

source files in repository into that dir Also adds CVS dir where it stores data about what you

check out cd ~ cvs checkout simplethreads cd simplethreads

Merge in new changes from repository (update): cvs update [files…]

Save your edited files into the repository so others can use them:

cvs commit –m “fixed annoying bugs” [files…]

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CVS Commands 2 Add a new file (source files .c or .h) to the repository

cvs add [files…] Check status of a file

cvs status file.c Check differences between your file and one in the

repository: cvs diff file.c cvs diff –r 1.1 file.c (specifies version)

View log of changes for a file cvs log file.c

Use emacs for cvs commit log editing (default is vi):

setenv VISUAL emacsMore info:

http://www.cvshome.org cvs --help-commands

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CVS Remote Access Access CVS from another machine besides

spinlock/coredump?: setenv CVSROOT

coredump.cs.washington.edu:/cse451/yourgroup/cvs

setenv CVS_RSH ssh

(for CVS to know how to access repository – use ssh)(add to ~/.login (csh) or ~/.profile (bash) to avoid typing…)

Warning: be wary of CVS on windows, OS X is ok