Programming

What I'm given:
Pure C code in one file that has to compile on Windows, SunOS, and AIX. My task is making minimal changes to the code to make it thread safe. I'm not in control of threads - they are created elsewhere. The code has a function invoked externally. The first call to this function is solitary. I.e. I'm guaranteed that no other call in any other thread will be made until it returns. It allows me to initialize mutexes during that call. The task seems very easy to accomplish with pthread library.

However, there is a complication. There are situations, when two consecutive calls to the function within a thread are related, and the first needs to pass some information to the next call. The natural way to accomplish it is to declare a thread local variable in global context. For this I use __thread directive, and it seems to work perfectly on SunOS. For AIX, on the other hand, this does not work. Since for our compilation we use the least common denominator for the broadest support, AIX complains that __thread directive is not compatible with the platform.

1. Is there anything AIX specific that allows to declare thread local variable in global context besides __thread directive?
2. What would be the most elegant (least code changes) work around?

Been a long time since I was foraging around in that sort of mess, but here's maybe a nudge. You didn't say anything about compiler / linkers or versions or OS versions or any of that sort of thing, so here's a possibility to follow up on if you're using this on the AIX box (-qtls option of XL C/C++ V9.0 for AIX):

IBM Compilers