Processes and Threads

1
What is a Thread?
A thread is similar to a process, but it
typically consists of just the flow of control.
Multiple threads use the address space of a
single process.
2
The Thread Model

• (a) Three processes each with one thread
• (b) One process with three threads

3
The Thread Model

• Items shared by all threads in a process
• Items private to each thread

4
The Thread Model

• Each thread has its own stack

5
Why Do We Use Threads?

• To simplify programs in which multiple activities
  go on at once.
• Easier to create and destroy because they have no
  resources attached to them - they share common
  memory.
• Performance gain, when there is substantial
  amounts of both computing and I/O.

• A word processor with three threads

6
A multithreaded Web server
7
Rough outline of code for web server

• (a) Dispatcher thread
• (b) Worker thread

8
Three ways to construct a server
9
Implementing Threads in User Space

• A user-level threads package

10
Implementing Threads in the Kernel

• A threads package managed by the kernel

11
Hybrid Implementations

• Multiplexing user-level threads onto kernel-
  level threads