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

12.4 Thread Safety

A hidden problem with threads is that they may call library functions that are not thread-safe, possibly producing spurious results. A function is thread-safe if multiple threads can execute simultaneous active invocations of the function without interference. POSIX specifies that all the required functions, including the functions from the standard C library, be implemented in a thread-safe manner except for the specific functions listed in Section 13.7 gives a thread-safe implementation called strerror_r.

Another interaction problem occurs when threads access the same data. The individual copier threads in Program 12.8 work on independent problems and do not interact with each other. In more complicated applications, a thread may not exit after completing its assigned task. Instead, a worker thread may request additional tasks or share information. Chapter 13 explains how to control this type of interaction by using synchronization primitives such as mutex locks and condition variables.

Section 2.7), and in most thread implementations errno is a macro that returns thread-specific information. In essence, each thread has a private copy of errno. The main thread does not have direct access to errno for a joined thread, so if needed, this information must be returned through the last parameter of pthread_join.