1. Understand Process Management
• Threads
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CPP TUTORIALS
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3. Recap
In the last class, you have learnt
• Relationship between Processes
• Reasons for providing an environment that allows
Process cooperation
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4. Objectives
On completion of this class, you would be able to
know
• Definition of Thread
• Benefits of Multithread programming
• Multithreading Models
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5. Thread Structure
• A thread is a light weight process (LWP)
• Basic unit of CPU utilization
• Shares other threads belonging to the same process its
code section, data section and other resources
• Threads created for a particular process are known as
sibling threads
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6. Thread Structure
Thread comprises of
• Thread id
• Program counter
• Register counter
• Register set
• Stack
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7. Thread Structure
• Process having multiple threads of control, can perform more
than one task at a time
• Threads operate, in many respects, in the same manner as
processes
• Like processes threads can share CPU, but only one thread at a
time is active
• Thread can create child threads
• Threads are not independent of one another
• This structure does not provide protection between threads as
they can read or write over any other thread
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8. Thread States
Thread states
• New
• Ready
• Blocked
• Running
• Terminated
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9. Threads
Single threaded process
• A traditional (or heavy weight) Process that has a single thread
of control
Multi threaded process
• A process which has several threads of control
• It can do more than one task at a time
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10. Single and Multi Thread Process
Thread
Single Thread Process Multi Thread Process
Fig.1
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11. Benefits of Multithreading Programming
Responsiveness
• Allows a program to continue even if a part of it is
blocked or performing a lengthy operation
Resource sharing
• Threads share the memory and the resources of the
process to which they belong
• Allows an application to have several different
threads of activity within the same address space
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12. Benefits of Multithreading Programming
Economy
• Threads share resources of the process to which
they belong
• Hence it is more economical to create and
conduct switch threads
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13. Benefits of Multithreading Programming
Utilization of multiprocessor architectures
• Benefits of multithreading can be greatly increased
in a multiprocessor architecture where threads may
be running in parallel on different processors
• Multithreading increases concurrency on a multi-
CPU machine
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14. Multi Threading Model
• An operating system support multiple threads of execution in
one process
• Support for threads may be provided at either the user level or
by the kernel
• User threads are supported above the kernel and are managed
without kernel support
• Kernel threads are supported and managed directly by
operating system
• Windows XP. Solaris, True64 UNIX - support kernel threads
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15. One process one thread One process multiple thread
Fig.1 (a) Fig.2 (b)
Multiple process, one thread per process Multiple process, multiple threads per process
Fig.3 (c) Fig.4 (d)
Fig: multithreading model 15

16. Multithreading Models
Many-to-one Model
• Maps many user-level threads to one kernel thread
• Green threads-a thread library available for Solaris users this
model
Fig.2
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17. Multithreading Models
One-to-One Model
• Maps each user thread to a kernel thread
• Windows 95/98/NT/2000/XP implement the one-to-one
model
User thread
Kernel thread
Fig.3
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18. Multithreading Models
Many-to-Many Model
• Multiplexes many user level threads to a smaller or equal
number of kernel threads.
User thread
Kernel thread
Fig.4
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19. Summary
In this class, you have learnt
• A thread is a basic unit of CPU utilization
• A thread is a light weight process
• A thread shares with peer threads its code section
data section and other resources
• Extensive sharing makes CPU switching among
peer threads and thread creation inexpensive
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20. Frequently Asked Questions
1. Write short notes on threads
2. Explain the different multithreading models
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21. Other subject materials
• Web designing
• Micro processors
• C++ tutorials
• java
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22. Quiz
State whether the following statements are true or false
1. Thread is a light weight process
a) True
b) False
2. Threads can communicate with each other
a) True
b) False
3. A thread needs __________________
Less no. of resources
4. A single process _____________________
Supports multiple threads
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