Hands-On System Programming with Linux

Thread safety via TSD

Prior to the TLS technique that we just saw (that is, before Linux 2.6 and gcc 3.3), how did one guarantee writing a new API to be thread safe? A much older technology exists, called TSD.

In a nutshell, TSD is a more complex solution from the application developer's viewpoint—more work must be done to achieve the very same end result that TLS so easily gives us; that of making a function thread-safe.

With TSD, the thread-safe routine must invoke an initializer function (usually done with pthread_once(3)), which creates a unique thread-specific data key (using the pthread_key_create(3) API). This initializer routine associates a thread-specific data variable (such as the iobuf buffer pointer in our example) with that ...