Multithreading Models

User and Kernel Threads

Kernel threads - threads supported by the Kernel (mac os, windows)

User threads - management done by user-level threads library

libraries include:

• POSIX Pthreads

• Windows threads

• Java threads

Many-to-One

• Many user-level threads mapped to single kernel thread

• One thread blocking causes all to block

• Multiple threads may not run in parallel on multicore system because only one may be in kernel at a time

• Few systems currently use this model

• Examples: Solaris Green Threads, GNU Portable Treads

One-to-One

• Each user-level thread maps to kernel thread

• Creating a user-level thread creates a kernel thread

• More concurrency than many-to-one

• Number of threads per process sometimes restricted due to overhead

• Examples: Windows, Linux

Many-to-Many

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

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

• Examples: Windows with ThreadFiber Package (otherwise its not common)

Two-level Model

• Similar to Many-to-Many, except that it allows a user thread to be bound to kernel thread