1. Chapter 4: Threads CSS503 Systems Programming
Prof. Munehiro Fukuda
Computing & Software Systems University of Washington Bothell
CSS503
Chapter 4: Thraeds

2. Thread Concepts Process-oriented computing Multithreaded computing
code
files
data
code
files
data
thread
code
files
data
process
code
files
data
code
files
data
process
Operating System
Operating System
CSS503
Chapter 4: Thraeds

3. Single vs Multithreaded Processes
Carries everything such as an address space, code, data, and files
Heavyweight in terms of creation/termination/context switching
Threads
Shares an address space, code, data and files if they belong to the same process
Lightweight in terms of creation/termination/context switching
Then, what is uniquely carried by each thread?
CSS503
Chapter 4: Thraeds

4. Benefits Responsiveness Deadlock avoidance
Scalability, (i.e., Utilization of multiprocessor architecture)
Resource sharing and economy
Threads share an address space, files, code, and data
Avoid resource consumption
Perform much a faster context swtich
CSS503
Chapter 4: Thraeds

5. Benefit 1: Responsiveness Multithreaded Server
Web Server
Clients
DB1
DB2
CGI
http
pages
CSS503
Chapter 4: Thraeds

6. Benefit 2: Deadlock avoidance
Process 1
Process 2
Bounded buffer
send
send
Bounded buffer
receive
receive
A sequence of send and then receive does not work!
Send and receive must be executed concurrently with threads.
CSS503
Chapter 4: Thraeds

7. Benefit 3: Utilization of multicore multiprocessor architecture
time = t
time = t + x
Place code, files and data in the main memory.
Distribute threads to each of CPUs, and
Let them execute in parallel.
time = t + 2x
code
files
data
CSS503
Chapter 4: Thraeds

8. User and Kernel Threads
User Threads
Thread Management Done by User-Level Threads Library
Examples
- POSIX Pthreads
- Win32 threads
- Java threads
Kernel does not care how many user threads exist.
Kernel Threads
Supported by the Kernel
- Linux
- Windows XP/2000
- Solaris lightweight processes
CSS503
Chapter 4: Thraeds

9. Many-to-One Model Advantage: fast
Many user-level threads mapped to a single kernel thread.
Used on systems that do not support kernel threads.
Examples: Solaris Green Threads, GNU Portable Threads
Advantage: fast
Disadvantage: 1. Non preemption or very
complicated to handle
preemption and I/O
2. No use of MP architecture
CSS503
Chapter 4: Thraeds

10. One-to-One Model Advantage: everything is supported by OS.
Each user-level thread maps to kernel thread.
Examples
- Windows NT/XP/2000
- Linux
- Solaris 9 or later
Advantage: everything is supported by OS.
Using MP architecture.
Disadvantage: slower than many-to-one model.
too many threads do not help.
CSS503
Chapter 4: Thraeds

11. Many-to-Many Model Covering the shortage of the previous two models
Examples: Windows XP’s fiber library, AIX Pthreads
CSS503
Chapter 4: Thraeds

12. Process Structure
Kernel schedules each light-weight process separately.
Traditional UNIX Process
Multithreaded Process
Process ID
Process ID
UID GID EUID EGID
UID GID EUID EGID
Directory Entry
Directory Entry
TTY
TTY
Signal Dispatch
Table
Signal Dispatch
Table
Memory Map
Memory Map
LWP1
LWP2
stdin
priority
stdin
LWP ID
LWP ID 1
stdout
Intr. mask 1
stdout
priority
priority 2
stderr
registers 2
stderr
Intr. mask
Intr. mask 3 3
registers
registers
CPU Status
File Descriptors
File Descriptors
CSS503
Chapter 4: Thraeds 11

13. Thread Structures Thead library runs in a user space.
Process
JVM
Java Threads
Thead library runs in a user space.
All threads shared the same address space.
Each thread maintains its own information and stack space.
Once a thread is mapped to a LWP, it runs on a CPU.
thread info
Thread3
stack
red zone
thread info
Thread2
stack
red zone
Thread1
thread info
stack
red zone
Thread ID
Thread ID
Thread ID
priority
priority
priority PC PC PC SP SP SP
Other regs
Other regs
Other regs
heap
Thread1
Thread2
Thread3
code + global data
Pthreads
Win32 threads
Thread to LWP mapping
User mode
Signal Dispatch
Table
Memory Map
File Descriptors
Directory Entry
UID GID EUID EGID
Process ID
TTY
LWP1
priority
Intr. mask
registers
LWP ID
LWP2
priority
Intr. mask
registers
LWP ID
Kernel mode
CSS503
Chapter 4: Thraeds 12

14. Discussion 1
Why can threads perform their context switch much faster than processes?
What data structure must threads carry by their own resource?
What data structure can they share?
What if we use processes rather than threads in the following cases we discussed.
Responsiveness
Deadlock avoidance
Utilization of multiprocessor architecture
CSS503
Chapter 4: Thraeds

15. 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
CSS503
Chapter 4: Thraeds

16. Thread Implementation Library and Class
Functions
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( )
CSS503
Chapter 4: Thraeds

17. Thread Implementation PThread 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 $
CSS503
Chapter 4: Thraeds

18. Thread Implementation Java Thread 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
CSS503
Chapter 4: Thraeds

19. Threading Issues Semantics of fork( ) and exec( )
Should all threads be duplicated?
Thread cancellation
Asynchronous cancellation
Deferred cancellation
Signal handling
Synchronous: illegal memory access
Asynchronous: a signal ^c from a shell
Thread pools
On-demand thread creation
A pool of threads upon a process creation
CSS503
Chapter 4: Thraeds

20. Thread Cancellation Asynchronous Deferred
#include <iostream>
using namespace std;
void thread_func( void *arg ) {
while ( true ) {
// do something ; }
cout << "terminated" << endl;
int main( ) {
pthread_t tid;
pthread_create( &tid, NULL, thread_func, NULL );
sleep( 10 );
pthread_kill( tid, SIGKILL );
pthread_join( tid, NULL );
cout << "joined" << endl;
$ ./a.out
Killed
What if a child thread acquired a lock that the parent needs later?
Deferred
#include <iostream>
using namespace std;
void *thread_func( void *arg ) {
bool &alive = *(bool *)arg;
while ( alive ) {
// do something ; }
cout << "terminated" << endl;
int main( ) {
pthread_t tid;
bool alive = true;
pthread_create( &tid, NULL, thread_func, (void *)&alive );
sleep( 10 );
alive = false;
pthread_join( tid, NULL );
cout << "joined" << endl;
$ ./a.out
terminated
joined
CSS503
Chapter 4: Thraeds

21. Signal Handling Synchronous: illegal memory access
void sigint_func( int sig ) {
// print out my id
pthread_t tid = pthread_self( );
printf( "%u caught SIGINT.\n", tid );
exit( 0 ); }
void sigfpe_func( int sig ) {
printf( "%u caught SIGFPE.\n", tid );
pthread_exit( NULL );
void *thread_func( void *arg ) {
int logical_id = *(int *)arg;
*(int *)arg = -1;
pthread_t child_tid = pthread_self( );
printf( "child[%d]'s tid = %u\n", logical_id, child_tid );
// have sigint_func catch ^C
signal( SIGINT, sigint_func );
// have sigfpe_func catch SIGFPE
signal( SIGFPE, sigfpe_func );
while ( true ) {
int i = 1, div = 0;
// have child[MAX - 1] cause a zero division error.
if ( logical_id == MAX - 1 ) {
div = i / div;
int main( ) {
// print out my id
pthread_t main_tid = pthread_self( );
printf( "main's pthread_t = %u\n", main_tid );
// create children
pthread_t tid[MAX];
for ( int i = 0; i < MAX; i++ ) {
int id = i;
pthread_create( &tid[i], NULL, thread_func, (void *)&id );
while ( id == i ); }
while ( true );
Synchronous: illegal memory access
received by the same thread
Asynchronous: a signal ^c from a shell
received by the main thread (Textbook: the first thread found)
CSS503
Chapter 4: Thraeds

22. Thread Pools The worker pool RMI Per-request threads CSS503
Client 1
Pick up a request
RMI server stub
Client 2
accept
Client 1
queue
RMImethod1( ) { :
pthread_create( );
pthread_kill( );
return; }
Client n
Client 2
Per-request threads
Client 1
Spawn for each request
accept
Client 2
Can it kill them at once?
Client n
CSS503
Chapter 4: Thraeds

23. Discussions 2
Why does the latest Java compiler deprecate the use of resume, suspend, and stop? Consider an undesired situation incurred when those three functions are used.
If we omit a join( ) statement in both the Pthread and Java versions (in p16 and p17), what happened to them. Do we observe any difference between them?
Why does Linux deliver asynchronous signals to the main thread?
CSS503
Chapter 4: Thraeds