What Are The Architectural Differences Between User Space Threads, And Kernel Supported Threads?

⟩ What are the Architectural differences between User-space threads, and Kernel-supported threads?

User-space threads live without any support from the

kernel; they maintain all of their state in user space.

Since the kernel does not know about them, they cannot be

scheduled to run on multiple processors in parallel.

Kernel-supported threads fall into two classes.

In a "pure" kernel-supported system, the kernel is

responsible for scheduling all threads.

Systems in which the kernel cooperates with a user-level

library to do scheduling are known as two-level, or hybrid,

systems. Typically, the kernel schedules LWPs, and the user-

level library schedules threads onto LWPs.

Because of its performance problems (caused by the need to

cross the user/kernel protection boundary twice for every

thread context switch), the former class has fewer members

than does the latter (at least on Unix variants). Both

classes allow threads to be run across multiple processors

in parallel.

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