Threads

Single and Multithreaded Processes


Benefits
------------
Responsiveness
Resource Sharing
Economy
Utilization of MP Architectures

User Threads
-------------
Thread management done by user-level threads library
Examples
    - POSIX Pthreads
    - Mach C-threads
    - Solaris threads

Kernel Threads
---------------
Supported by the Kernel
Examples
    - Windows 95/98/NT/2000
     - Solaris
    - Tru64 UNIX
    - BeOS
    - Linux


Multithreading Models
----------------------
Many-to-One
One-to-One
Many-to-Many

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


One-to-One
-----------
Each user-level thread maps to kernel thread.
Examples
    - Windows 95/98/NT/2000
    - OS/2
One-to-one Model


Many-to-Many Model
-------------------
Allows many user level threads to be mapped to many kernel threads.
Allows the  operating system to create a sufficient number of kernel threads.
Solaris 2
Windows NT/2000 with the ThreadFiber package
Many-to-Many Model



Threading Issues
-----------------
Semantics of fork() and exec() system calls.
Thread cancellation.
Signal handling
Thread pools
Thread specific data

Pthreads
---------
a POSIX standard (IEEE 1003.1c) API for thread creation and synchronization.
API specifies behavior of the thread library, implementation is up to development of the library.
Common in UNIX operating systems.
Solaris 2 Threads
 
Solaris Process

Windows 2000 Threads
---------------------
Implements the one-to-one mapping.
Each thread contains
    - a thread id
    - register set
    - separate user and kernel stacks
    - private data storage area

Linux Threads
--------------
Linux refers to them as tasks rather than threads.
Thread creation is done through clone() system call.
Clone() allows a child task to share the address space of the parent task (process)

Java Threads
-------------
Java threads may be created by:
 - Extending Thread class
 - Implementing the Runnable interface
Java threads are managed by the JVM.