1. Introduction

1. Introduction
	Chapter 3. Threads

Threads
- Definition:
  - A thread is a single sequential flow of control within a program.
  - A thread runs within the context of a program's process and takes advantage of the resources allocated for that process and its environment.
- Multiple threads:
  - Multiple threads can run at the same time in the same process performing different tasks.
  - Multiple threads can share the resources of the process they share.
    Figure 3.1. Multiples Threads
Advantages of Multithreading
- Improve applications responsiveness
- Use multiprocessors efficiently.
- Improve program structure.
- Use fewer system resources
- Improve performance.
  Threads X Processes:
- In traditional UNIX each process contains a single thread, so programming with multiple processes is programming with multiple threads.
- Because a process is also an address space creating a process is expensive, while creating a thread within an existing process is cheap.
- The time it takes to create a thread is on the order of a thousand times less than the time it takes to create a process.
- Communicating between the threads of one process is simple because the threads share everything-address space, in particular.
User-level Threads
User-level threads are handled in user space:
- They reduce kernel context switching penalties.
- They are visible only from within the process, where they share all process resources like address space, open files, and so on.
- When a thread needs to interact with other threads in the same process, it can do so without involving the operating system, reducing context switching penalties.
- An application can have thousands of threads and still not consume many kernel resources.


Chapter 3. Threads		2. Lightweight Process