33.4. Thread Implementation Models

In this section, we go into some theory, briefly considering three different models for implementing a threading API. This provides useful background for Section 33.5, where we consider the Linux threading implementations. The differences between these implementation models hinge on how threads are mapped onto kernel scheduling entities (KSEs), which are the units to which the kernel allocates the CPU and other system resources. (In traditional UNIX implementations that predate threads, the term kernel scheduling entity is synonymous with the term process.)

33.4.1.

33.4.1.1. Many-to-one (M:1) implementations (user-level threads)

In M:1 threading implementations, all of the details of thread creation, scheduling, and synchronization (mutex locking, waiting on condition variables, and so on) are handled entirely within the process by a user-space threading library. The kernel knows nothing about the existence of multiple threads within the process.