The Linux Programming Interface

31THREADS: THREAD SAFETY AND PER-THREAD STORAGE

This chapter extends the discussion of the POSIX threads API, providing a description of thread-safe functions and one-time initialization. We also discuss how to use thread-specific data or thread-local storage to make an existing function thread-safe without changing the function’s interface.

31.1 Thread Safety (and Reentrancy Revisited)

A function is said to be thread-safe if it can safely be invoked by multiple threads at the same time; put conversely, if a function is not thread-safe, then we can’t call it from one thread while it is being executed in another thread. For example, the following function (similar to code that we looked at in Section 30.1) is not thread-safe:

static int glob = ...