Unix™ Systems Programming [Electronic resources] : Communication, Concurrency, and Threads نسخه متنی

13.7 A strerror_r Implementation

Unfortunately, POSIX lists strerror as one of the few functions that are not thread-safe. Often, this is not a problem since often the main thread is the only thread that prints error messages. If you need to use strerror concurrently in a program, you will need to protect it with mutex locks. Neither perror nor strerror is async-signal safe. One way to solve both the thread-safety and async-signal-safety problems is to encapsulate the synchronization in a wrapper, as shown in Program 13.17.

The perror_r and strerror_r functions are both thread-safe and async-signal safe. They use a mutex to prevent concurrent access to the static buffer used by strerror. The perror function is also protected by the same mutex to prevent concurrent execution of strerror and perror. All signals are blocked before the mutex is locked. If this were not done and a signal were caught with the mutex locked, a call to one of these from inside the signal handler would deadlock.