Implementation

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.