css434 os support1 css434 operating system support textbook ch7 professor: munehiro fukuda

CSS434 OS Support 1

CSS434 Operating System SupportCSS434 Operating System SupportTextbook Ch7Textbook Ch7

Professor: Munehiro Fukuda

CSS434 OS Support 2

Outline Processes Threads

Pthread Java Thread

Multithreaded client and server design

The role of OS/Network for RPC Microkernel

CSS434 OS Support 3

System Layers

Applications, services

Computer &

Platform

Middleware

OS: kernel,libraries & servers

network hardware

OS1

Computer & network hardware

Node 1 Node 2

Processes, threads,communication, ...

OS2Processes, threads,communication, ...

CSS434 OS Support 4

ProcessesDefinition and Aspects

An environment to execute a program A process consists of:

A CPU register set (including program counter)

An dependent address space including Text (code) Data (global data) Stack (local variables) Heap (dynamic data)

Files Communication resources (sockets) Threads and their synchronization

facility

text

heap

stack

data

0

2N

Address Space

IDProcess Control Block

PC

SP

fd[64]

TCB

socket

CSS434 OS Support 5

ProcessesCreation and Resource Sharing

A parent process creates child processes through fork( ).

A child process overloads a new program on it through execve( ).

Execution They run in concurrent. A parent may wait for the

termination of a child through wait( ).

Resource sharing Resource inherited by

children: file descriptors, shared memory and system queues

Resource not inherited by children: address space

socket

IDParent’s PCB

PCSP

fd[64]TCB

text

heap

stack

data

0

2N

Address Space

Sharedmemory

IDChild’s PCB

PCSP

fd[64]TCB

text

heap

stack

data

0

2N

Address Space

Sharedmemory

copy

shared

shared

shared

CSS434 OS Support 6

ProcessesCreation and Copy-on-Write

Upon creating a child process A virtual address space is

allocated to a child. Corresponding physical

memory is still mapped to its parent.

Upon a write operation, physical memory is allocated to a child and data is copied.

text

text

data

data

stack

Sharedmemory

text

data

stack

Sharedmemory

stack

Sharedmemory

Physical address space Parent’s virtual address space

Child’s virtual address space

w

dataw

dataw

w

w

w

CSS434 OS Support 7

ProcessesCreation and Load Balancing

Transfer policy: Create a new process Locally Remotely → Location Policy

Static: transfer processes to predefined destinations Adaptive:transfer processes to destinations based on

run-time information Centralized load-sharing: A load manager take care

of correcting info and migrating processes. Hierarchical load-sharing: A system consists of a

tree structure where each node takes care of its child processes for load balancing

Decentralized load-sharing Sender-initiated: A heavy-loaded node sends

out a new process. Receiver-initiated: A light-loaded node

advertises its existence.

CSS434 OS Support 8

Threads Threads:

The basic unit of CPU utilization Control of Program Process can have two or more

parallel controls of program → multiple threads.

Belong to the same process. No protection between

threads. Advantages:

Light creation Light context switch Suitable to parallel computing Natural form of resource

sharingdata

text

Stack A

Stack B

Stack C

heap

o

2N

IDProcess Control Block

fd[64]

TCB

IDThread A

PC

SP

IDThread B

PC

SP

IDThread C

PC

SP

CSS434 OS Support 9

Threads v.s. Multiple Processes

Server consisting of Threads Multiple Processes

Creation Light overhead Heavy overhead

Context switch Cheap Expensive

Remote object sharing

Easy Needs shared memory

Priority Easy to change Not quite dynamically changeable

Protection Vulnerable Safe

Maybe, we can implement a server of multiple processes?

CSS434 OS Support 10

Thread ImplementationLibrary and Class

LibraryFunctions

Java Pthread Solaris Thread

Create a new thread new Thread( ) pthread_create( ) thr_create( )

Terminate myself destroy( ) pthread_exit( ) thr_exit( )

Wait for a given thread to be terminated join( ) pthread_join( ) thr_join( )

Terminate a given thread stop( ) pthread_kill( ) thr_kill( )

Get my thread object currentThread( )

pthread_self( ) thr_self( )

Relinquish CPU and put myself in a ready queue

yield( ) thr_yield( )

Suspend a given thread suspend( ) thr_suspend( )

Resume a give thread resume( ) thr_continue( )

Get my current running priority getPriority( ) pthread_getschedparam( )

thr_getprio( )

Change my current running priority setPriority( ) pthread_setschedparam( )

thr_setprio( )

Wait for another thread to signal me wait( ) pthread_cond_wait( ) cond_wait( )

Signal another thread waiting for me signal( ) pthread_cond_signal( ) cond_signal( )


Thread ImplementationC++ Example

#include <iostream>#include <string>using namespace std;

#include <pthread.h>#include <unistd.h>

void* thread_func( void *param ) {

for ( int i = 0; i < 5; i++ ) { sleep( 2 ); cout << "I'm a slave: " << *( (string *)param ) << endl; } return NULL;}

void main( int argc, char *argv[] ){ pthread_t child; string arg;

cout << "enter message: "; cin >> arg; pthread_create( &child, NULL, thread_func, (void *)&arg ); for ( int i = 0; i < 10; i++ ) { sleep( 1 ); cout << "I'm a master: " << arg << endl; } pthread_join( child, NULL ); cout << "Master synched with slave" << endl;}

$ g++ thread.cpp -lpthread$ a.outenter message: hello!I'm a master: hello!I'm a slave: hello!I'm a master: hello!I'm a master: hello!I'm a slave: hello!I'm a master: hello!I'm a master: hello!I'm a slave: hello!I'm a master: hello!I'm a master: hello!I'm a slave: hello!I'm a master: hello!I'm a master: hello!I'm a slave: hello!I'm a master: hello!Master synched with slave$

Compilation and Execution Source Code


Thread ImplementationJava Example

public class MyThread { public static void main( String args[] ) {

String arg = args[0];ThreadFunc child = new ThreadFunc( arg );child.start( );for ( int i = 0; i < 10; i++ ) { try {

Thread.sleep( 1000 ); } catch ( InterruptedException e ) { }; System.out.println( "I'm a master: " + arg );}try { child.join( );} catch ( InterruptedException e ) { };System.out.println( "Master synched with slave" );

}

}public class ThreadFunc extends Thread { public ThreadFunc( String param ) {

this.param = param; } public void run( ) {

for ( int i = 0; i < 5; i++ ) { try {

Thread.sleep( 2000 ); } catch ( InterruptedException e ) { }; System.out.println( "I'm a slave: " + param );}

} String param;}

$ lsMyThread.java ThreadFunc.java$ javac MyThread.java$ java MyThread hello!I'm a master: hello!I'm a slave: hello!I'm a master: hello!I'm a master: hello!I'm a slave: hello!I'm a master: hello!I'm a master: hello!I'm a slave: hello!I'm a master: hello!I'm a master: hello!I'm a slave: hello!I'm a master: hello!I'm a master: hello!I'm a slave: hello!I'm a master: hello!Master synched with slave$

Compilation and Execution

MyThread.java

ThreadFunc.java


Client and Server with Threads

Client: Can avoid a block on RPC by

having two threads. Server:

Assume: A request consists of 2ms processing and 4ms disk I/O.

Single-threaded Server Needs 6ms for a request Can process 166

request/second If three threads pick up and work

on a request in turn: Can overlap processing and

I/O Can process 1000/4 =250

request/second.

Client Server

RPCRequestqueue

RPCthread

Computationthread

requests


Multithreaded ClientsArchitecture

Why Multithreaded Clients Hide network latency

Main Thread: Interacts with a client user Work on computation Dispatch a request to a

child thread Child threads

Sends a request to a given server through TCP or RPC.

Waits for a response Forwards a response to

the main.

Client

Child ThreadsMain thread

User request Server 1RPC or TCP

request Server 2RPC or TCP



response

Pick up

Enqueue


Multithreaded ClientsExample

Web browser Requests and reads the

main HTML file. For each <img

src=“…”>, <object>, <applet>, etc.,

Spawns a child thread Child threads:

Sets up an HTTP connection

Reads each web part.

Web browser

Child ThreadsMain thread

User Request the main HTML ServerHTTP

Spawn a thread ServerHTTP

Server

<html>……

Scan the file

img

Spawn a threadHTTP

applet


Multithreaded ServersArchitecture

Dispatcher-worker model The worker pool (a) Per-request threads (b) Per-connection threads

(c) Team model

Per-object threads (d) Pipeline model (e)

queueaccept

accept

acceptaccept

Remote object

Remote object

Remote object

process

response

request

request

request

Spawn for each request

Spawn for each session

Session

Pick up a request(a) (b)

(c) (d) (e)


Multithreaded ServersExample

Object Server Instantiates remote

objects Associates each with

an independent thread

Let a thread maintain and protect its object

Requests Accepted at request

dispatcher Forwarded to an

object wrapper including objects residing under the same policy

Picked up by the destination thread

file A

stub

Per-objectthread

file B

stub

Per-objectthread

file C

stub

Per-objectthread

Object wrapper

req que

Request dispatcher

cgi 1

stub

Per-objectthread

cgi 2

stub

Per-objectthread

cgi 3

stub

Per-objectthread

Object wrapper

req que

Server

Client requests

Daemon thread mayServer for per-object threads

Thread Group


Thread/OS Interaction in RPC

Control transfer viatrap instruction

User Kernel

Thread

User 1 User 2

Control transfer viaprivileged instructions

Thread 1 Thread 2

Protection domainboundary

(a) System call

(b) RPC/RMI (within one computer)

Kernel

(c) RPC/RMI (between computers)

User 1 User 2

Thread 1 Network Thread 2

Kernel 2Kernel 1


OS and Network Interaction in RPC

1000 2000

RPC delay

Requested datasize (bytes)

Packetsize

0

Why does this gap occurs if a RPC arguments grow beyond a packet size?


Monolithic kernel and microkernel

Monolithic Kernel Microkernel

Server: Dynamically loaded server program:Kernel code and data:

.......

.......

Key:

S4

S1 .......

S1 S2 S3

S2 S3 S4

Unix, Sprite:non-modular way, intractable

WindowsNT:layering and OO design but stillmassive.

Mach, Chorus:modularity, portability, andextensibility


Role of the microkernelMiddleware

Languagesupport

subsystem

Languagesupport

subsystem

OS emulationsubsystem ....

Microkernel

Hardware

The microkernel supports middleware via subsystems

Microkernel facilitates only address spaces, threads and local inter-process communication.Middleware can use directly Microkernel for better performance or system processesfor convenience and flexible operations


Exercises (No turn-in)1. Textbook p333, Q7.7: Explain the advantage of copy-on-write region copying for Unix, where a call to for

k is typically followed by a call to exec. What should happen if a region that has been copied using copy-on-write is itself copied?

2. Why can threads perform their context switch faster than processes?3. What are the thread groups? What are the daemon threads? How can those contribute to the multithrea

ded server?4. If you comment out the following statement from the C++ code on Slide 11, what change will you obser

ver in the execution?1. pthread_join( child, NULL );

5. If you comment out the following statement from the Java code on Slide 12, what change will you observe in the execution?

6. child.join( );7. Textbook p333, Q7.8: A file server uses caching, and achieves a hit rate of 80%. File operations in the

server costs 5ms of CPU time when the server finds the requested block in the cache, and take an additional 15ms of disk I/O time otherwise. Explaining any assumptions you made, estimate the server’s throughput capacity (average requests/sec) if it is:

1. Signle-threaded;2. Two-threaded, running on a single processor;3. Two-threaded, running on a two-processor computer.

8. Textbook p333 Q7.16: Network transmission time accounts for 20% of a null RPC and 80% of an RPC that transmits 1024 user bytes (less than the size of a network packet). By what percentage will the times for these two operations improve if the network is upgraded from 10Mbps to 100Mbps.


Exercises (No turn-in)Q8. The following server code assumes that each client program asks three user inputs:

(1) the id of a file to operate on : 0 or 1, each corresponding “file0” and “file1”(2) a file operation type: ‘r’ as a file read or ‘w’ as a file write(3) if the file operation is ‘w’, a 100-byte message to be read from a keyboard.

The client sends those inputs to the server through a socket. If the file operation type is ‘r’, it receives a 100-byte content of the corresponding file from the server and prints it out.

The server spawns two child threads: child_thread[0] and childe_thread[1], each associated with socket descriptor sd[0] and sd[1] respectively. Every time the server accepts a new socket request from a client, it receives a file id from the client, and passes this socket request to the corresponding thread. The thread opens its file, checks a file operation type, and reads/writes the file according to the type.

Q8-1. Which server model was used in this tcp.cpp program, worker pool, per-request threads, per-connection threads, per-object threads, or pipeline model? Choose one of these models and justify your choice.

Q8-2. The server in the above program is not so scalable. In other words, it can’t handle many client requests concurrently. Why? Explain the reason.

Q8-3. Which server model(s) are scalable? If you change this program into such server model(s), what side effect will occur? Describe the major problem you have conceived.


Exercises (No turn-in)#include "Socket.h"#include "pthread.h"#define PORT 10000#define SIZE 100 // message sizeint sd[2]; // socket descriptorvoid* thread_func( void *arg ) { // thread to read and write a given file int id = *(int *)arg; // my thread id char fileName = (id == 0) ? "file0" : "file1"; // if I'm 0, operate on file0 while ( true ) { if ( sd[id] == NULL_FD ) // check if a new socket request came to me. continue; int fd = open( fileName, O_RDWR );// open my file char op; // a file operation type: 'r' or 'w' read( sd[id], &op, 1 ); // read an operation type from the socket if ( op[id] == 'r' ) { // a read operation read( fd, message, SIZE ); // read 100 bytes from my file write( sd[myId], message, SIZE ); // send them back to the client } else if ( op[id] == 'w' ) { // a write operation read( sd[myId], message, SIZE ); // receive 100 bytes from the client write( fd, message, SIZE ); // write them down to my file } close( fd ); // close my file close( sd[Id] ); // close this socket conneciton sd[Id] = NULL_FD; // inform the server that I'm ready } }


Exercises (No turn-in)int main( int argc, char *argv[] ) { int sd = NULL_FD; // socket descriptor char id = 0; // a file (thread) id if ( argc == 1) { // I'm a server pthread_t child[2]; for ( int i = 0; i < 2; i++ ) { // create two child threads sd[i] = NULL_FD; pthread_create( &child[0], NULL, thread_func, (void *)&i ); } while ( true ) { // keep receiving a client socket request if ( ( sd = sock.getServerSocket( ) ) == NULL_FD )

return -1; read( sd, &id, 1 ); // receive a file (thread) id while ( sd[id] != NULL_FD )

; // wait for cihld_thread[id] to be ready sd[id] = sd; // pass this client socket to the thread } } if ( argc == 2 ) { // I'm a client if ( ( sd = Sock.getClientSocket( argv[1] ) ) == NULL_FD ) return -1; cout << "Operate on file0 or file1? (type 0 or 1): "; cin >> id; write( sd, id, 1 ); // send a file (thread) id to server cout << "Operation type? (type r or w): "; cin >> op; write( sd, &op, 1 ); // send a file operation type to server if ( op == 'w' ) { // if it's a write operation cout << "message: "; cin >> message; // read a user message write( sd, message, SIZE ); // send it to the server } if ( op == 'r' ) { // if it's a read operation read( sd, message, SIZE ); // receive a message from server cout << message << endl; // display it } }}

css434 os support1 css434 operating system support textbook ch7 professor: munehiro fukuda

Documents

child processes

css434 os support1 css434

transfer processes

parent process

css434 os support9 threads

dependent address space

new process

multiple processes server