1. Threads: Light-Weight Processes
CS 314 Operating Systems
Threads: Light-Weight Processes
Department of Computer Science
Southern Illinois University Edwardsville
Spring, 2019
Dr. Hiroshi Fujinoki
UK_Threads/000

2. CS 314 Operating Systems Processes and Threads  Problems in processes
 Concept of threads
 How do threads solve the problem in processes?
 Two different thread implementations
UK_Threads/001

3. CS 314 Operating Systems Processes and Threads  Problems in processes
High overhead in inter-process-communication (IPC)
High context-switching overhead in multitasking using processes
UK_Threads/002

4. CS 314 Operating Systems Processes and Threads  Problems in processes
High overhead in inter-process-communication (IPC)
Processes can not access memory
address outside of its address space
Memory address
space for each
process
Memory P1 P2 P3
Data in
Memory
What if, some process need to share
some information (data)?
Processes exchange information
through OS (IPC)
“shared memory”
“pipe” OS
“semaphore”
“message passing”
UK_Threads/003

5. CS 314 Operating Systems Processes and Threads  Problems in processes
High overhead in inter-process-communication (IPC)
Processes can not access memory
address outside of its address space
Memory P1 P2 P3
What if, some process need to share
some information (data)?
move it to
shared memory
Processes exchange information
through OS (IPC)
Shared Memory
OS performs
this operation
“shared memory”
“pipe” OS
“semaphore”
“message passing”
UK_Threads/003

6. CS 314 Operating Systems Processes and Threads  Problems in processes
The high-overhead IPC’s
are acceptable for
loosely-coupled processes
 Problems in processes
High overhead in inter-process-communication (IPC)
Processes can not access memory
address outside of its address space
Memory address
space for each
process
Memory P1
What if, some process need to share
some information (data)? P2 P3
system call
Processes exchange information
through OS (IPC)
Closely-coupled processes
Keyboard input
“shared memory”
Background spell-check
“pipe” OS
Automatic file-save
“semaphore”
“message passing”
UK_Threads/004

7. CS 314 Operating Systems Processes and Threads  Problems in processes
High context-switching overhead in multitasking using processes
Memory
Processor P1 P2
Registers
   P3
SAVE
LOAD
Time
PCB-P1
PCB-P2
PCB-P3 OS
UK_Threads/005

8. CS 314 Operating Systems Processes and Threads  Problems in processes
The high-overhead IPC’s
are acceptable for
loosely-coupled processes
 Problems in processes
High context-switching overhead in multitasking using processes
Closely-coupled processes
Memory
Keyboard input
Processor P1
Background spell-check
Automatic file-save P2
Registers
   P3
SAVE
LOAD
Time
PCB-P1
PCB-P2
PCB-P3 OS
UK_Threads/006

9. CS 314 Operating Systems Processes and Threads  Concept of threads P1
Memory
Memory OS P1
Thread1
Thread2
Thread3
Process P2 P3 OS
UK_Threads/007

10. CS 314 Operating Systems Processes and Threads  Concept of threads
Global
Variable Area
 Concept of threads
Memory
Memory P1
Thread1
Process
Address
Space P2
Thread2
Thread3 P3 OS OS
UK_Threads/008

11. CS 314 Operating Systems Processes and Threads
 How do threads solve the problem in processes?
High overhead in inter-process-communication (IPC)
High context-switching overhead in multitasking using processes
UK_Threads/009

12. CS 314 Operating Systems Processes and Threads
Inter-process
communications
must go through
OS (system call)
The member threads
can access shared data
w/out going through
a system call
Processes and Threads
Solved 
 How do threads solve the problem in processes?
High overhead in inter-process-communication (IPC)
Memory OS P1 P2 P3
system call
IPC by
“message passing”
Memory OS P1 P2 P3
Shared Memory
move it to
shared memory
OS performs
this operation
IPC by
“shared memory”
Memory
Thread1
Thread2
Thread3 OS
UK_Threads/010

13. CS 314 Operating Systems PCB Processes and Threads
 How do threads solve the problem in processes?
High context-switching overhead in multitasking using processes
PCB
TCB
TCB is a subset of PCB
UK_Threads/011

14. CS 314 Operating Systems PCB Processes and Threads
 How do threads solve the problem in processes?
High context-switching overhead in multitasking using processes
PCB
TCB
TCB
TCB
TCB
TCB is a subset of PCB
UK_Threads/012

15. CS 314 Operating Systems PCB Processes and Threads
 How do threads solve the problem in processes?
High context-switching overhead in multitasking using processes
PCB
TCB
TCB
TCB
TCB
TCB is a subset of PCB
UK_Threads/013

16. CS 314 Operating Systems PCB Processes and Threads
Solved 
 How do threads solve the problem in processes?
High context-switching overhead in multitasking using processes
PCB
TCB
User ID
Total CPU time
Total amount of memory
TCB
TCB
TCB
TCB is a subset of PCB
UK_Threads/014

17. CS 314 Operating Systems Processes and Threads
 How do threads solve the problem in processes?
High context-switching overhead in multitasking using processes
Memory
Memory
Where are “TCB’s”? P1
Thread1
Thread2
Thread3
Processor
  
Registers
Process P2 P3
PCB-P1
PCB-P2
PCB-P3 OS OS
PCB
UK_Threads/015

18. CS 314 Operating Systems Processes and Threads
 Two different thread implementations
Kernel-Mode
Threads
OS manages each thread
(as well as processes)
Thread
Implementation
OS has thread manager (scheduler)
Application-Mode
Threads
A.K.A. “OS-mode threads”
OS does NOT manage each
thread (it manages only processes)
OS does not have thread manager
A.K.A. “user-mode threads”
UK_Threads/016

19. CS 314 Operating Systems Processes and Threads Thread1 Thread1 Thread2
Kernel-Mode
Threads
Application-Mode
Threads
Memory
Memory
Thread1
Thread1
Thread2
Thread2
Thread3
Thread3
Process
Scheduler
Process
Scheduler OS OS
Thread
Scheduler
= PCB
= TCB
UK_Threads/017

20. CS 314 Operating Systems Processes and Threads Thread1 Thread1 Thread2
Kernel-Mode
Threads
Application-Mode
Threads
Memory
Memory
Thread1
Thread1
Thread2
Thread2
Thread3
Thread3
Thread
Scheduler
Process
Scheduler
Process
Scheduler OS OS
Thread
Scheduler
= PCB
= TCB
UK_Threads/018

21. CS 314 Operating Systems Processes and Threads Process T1 T2 Process
System call
Function call (faster than system call)
Process T1
Kernel-Mode
Threads T2
Process T3 OS
Process
Thread Scheduler T1
Process T2
Application-Mode
Threads T3 OS
UK_Threads/019