Thread

• A thread (or lightweight process) is a basic unit of CPU utilization; it consists of:

o Thread ID
o program counter
o register set
o stack space

• A thread shares with its peer threads its:

o code section
o data section
o operating-system resources

• A traditional or heavyweight process has a single thread of control.

• In a multiple threaded task, while one server thread is blocked and waiting, a

second thread in the same task can run.
o Cooperation of multiple threads in same job confers higher throughput
and improved performance.
o Applications that require sharing a common buffer (i.e., producer-
consumer) benefit from thread utilization.

• Threads provide a mechanism that allows sequential processes to make

blocking system calls while also achieving parallelism.

Single Threaded Process




Multi-Threaded Process

Benefits of Multi Threaded Programming

• Responsiveness
• Resource Sharing
• Economy
• Utilization of MP Architectures

User Thread

• Thread management done by user-level threads library

• Fast to create and manage threads

• If the kernel is single-threaded, then any user-level thread per

blocking system call will cause the entire process to block

• Examples

- POSIX Pthreads
- Mach C-threads
- Solaris UI-threads

Kernel Thread

• Supported by the Kernel
• Slower to create and manage threads than are user threads
• If a thread performs a blocking system call, then the kernel can schedule
  

another thread in the application for execution.

• Multiple threads are able to run in parallel on multiprocessors.
• Examples
  

- Windows NT/2000
- Solaris 2
- Tru64 UNIX
- BeOS
- Linux

Thread Library

• A thread library provides the programmer with an API for creating and managing threads

• Three main libraries:

-POSIX Pthreads

-Win32

-Java

Multithreading Models

• Many-to-One Model
• One-to-One Model
• Many-to-Many Model
  

Many-to-One Model

• Many user-level threads mapped to single kernel thread
• Used on systems that do not support kernel threads.

• Allows many user level threads to be mapped to many kernel thread

• Allows the operating system to create a sufficient number of kernel threads

• Solaris prior to version 9

• Windows NT/2000 with the ThreadFiber package

n

One-to-One Model

• Each user-level thread maps to kernel thread.
• Creating a user thread requires creating the corresponding kernel thread.
• Windows NT/2000, OS/2
• Each user-level thread maps to kernel thread
• Examples

  -Windows NT/XP/2000

  -Linux

  -Solaris 9 and later