1. CSS490 Process Management
Textbook Ch8
Instructor: Munehiro Fukuda
These slides were compiled from the course textbook, the reference books, and the instructor’s original materials.
Hello! Everyone,
My name is Shinya Kobayashi. Today, I am going to present our paper titled “Inter-Cluster Job Coordination Using Mobile Agents” on behalf of the first author, Munehiro Fukuda. Munehiro was hoping to show up and present the paper at AMS2001, however he got to wait in Japan until he will get an H1B visa. Since I received the presentation materials from him quite recently, please allow me to present this paper using this script.
I can respond to your questions as far as I know, however you can also ask Munehiro by . His address is on the title page of our paper.
(time 1:05)
Winter, 2004
CSS490 Process Management

2. Processes Definition 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 2N
Address Space ID
Process Control Block PC SP
fd[64]
TCB
socket
Winter, 2004
CSS490 Process Management

3. Processes Creation 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 ID
Parent’s PCB PC SP
fd[64]
TCB
text
heap
stack
data 2N
Address Space
Shared
memory ID
Child’s PCB PC SP
fd[64]
TCB
text
heap
stack
data 2N
Address Space
Shared
memory
copy
shared
shared
socket
shared
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CSS490 Process Management

4. Processes Creation and Copy-on-Write
Physical address space
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.
Parent’s virtual address space
data
data w
Shared
memory w
data
stack
text
Shared
memory w
Child’s virtual address space
data w
text
Shared
memory w
stack
stack
text
Winter, 2004
CSS490 Process Management

5. Processes Creation 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.
Winter, 2004
CSS490 Process Management

6. CSS490 Process Management
Threads
data
text
Stack A
Stack B
Stack C
heap o 2N ID
Process Control Block
fd[64]
TCB
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 sharing ID
Thread A PC SP ID
Thread B PC SP ID
Thread C PC SP
Winter, 2004
CSS490 Process Management

7. Client and Server with Threads
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
RPC
Request
queue
thread
Computation
requests
Winter, 2004
CSS490 Process Management

8. Multithreaded Clients Architecture
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
Main thread
Child Threads
User
request
Server 1
RPC or TCP
Pick up
request
Server 2
RPC or TCP
response
request
Server 3
RPC or TCP
RPC or TCP
request
Server 4
Enqueue
Winter, 2004
CSS490 Process Management

9. Multithreaded Clients Example
Web browser
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.
Main thread
Child Threads
User
Request the main HTML
HTTP
Server
<html> …
Scan the file
HTTP
Spawn a thread
Server
img
HTTP
Spawn a thread
Server
applet
Winter, 2004
CSS490 Process Management

10. Multithreaded Servers Architecture
Dispatcher-worker model
The worker pool (a)
Per-request threads (b)
Per-connection threads (c)
Team model
Per-object threads (d)
Pipeline model (e)
(a)
(b)
Pick up a request
Spawn for each request
accept
queue
accept
(c)
(d)
Session
Remote object
(e)
request
accept
accept
Spawn for each session
request
Remote object
process
request
Remote object
response
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CSS490 Process Management

11. Multithreaded Servers Example
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-object
thread
file B
file C
Object wrapper
req que
Request dispatcher
cgi 1
cgi 2
cgi 3
Server
Client requests
Thread Group
Daemon thread may
Server for per-object threads
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CSS490 Process Management

12. Threads v.s. Multiple Processes
Maybe, we can implement a server of 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
Winter, 2004
CSS490 Process Management

13. Thread Implementation Library and Class
Functions
Java
Pthread
Solaris Thread
Create a new thread
wew 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( )
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CSS490 Process Management

14. Thread Implementation C++ 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;
Compilation and Execution
Source Code
$ g++ thread.cpp -lpthread
$ a.out
enter message: hello!
I'm a master: hello!
I'm a slave: hello!
Master synched with slave $
Winter, 2004
CSS490 Process Management

15. Thread Implementation Java Example
MyThread.java
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 ); }
child.join( );
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++ ) {
Thread.sleep( 2000 );
System.out.println( "I'm a slave: " + param );
String param;
Compilation and Execution
$ ls
MyThread.java ThreadFunc.java
$ javac MyThread.java
$ java MyThread hello!
I'm a master: hello!
I'm a slave: hello!
Master synched with slave $
ThreadFunc.java
Winter, 2004
CSS490 Process Management

16. Exercises (No turn-in)
Why is the copy-on-write technique so effective?
Why can threads perform their context switch faster than processes?
What are the thread groups? What are the daemon threads? How can those contribute to the multithreaded server?
If you comment out the following statement from the C++ code on Slide 14, what change will you observer in the execution?
pthread_join( child, NULL );
If you comment out the following statement from the Java code on Slide 15, what change will you observe in the execution?
child.join( );
Winter, 2004
CSS490 Process Management