After having been off the list for a while now, because of other things to do, I'd like to share some thought about the still not solved question of TLS on Windows. As far as I remember the original author of the thread library (Bill Kempf) intended the thread local storage to be usable in an orthogonal way to boost::threads, i.e. TLS should be cleaned up even when used in the context of native threads. He came up with a solution of using a DLL to catch the very last breath of the thread. (I proposed a "piggy pack" DLL that can be embedded in the main executable, to get rid of the need to separately distribute a DLL file.) Now while rethinking the thing I have serious reservations about the DLL solution: The exit and cleanup is getting called AFTER the C-runtime library has been de-initialized for the thread. Is it save then to call any of the library functions in the yet "zombied" thread? May I even call free or delete on objects that have been created in context of the thread? Extending this question to threads that have been created by other means (including boost::thread) this means the exit handler must not access any features that have been in control of the thread mechanism. For me this means either to drop the (desirable) requirement of orthogonality and require the thread beeing created and managed by boost when using TLS, or force the user to obey strict rules about what she is allowed to do in an exit handler (destructor in turn of an object). To me the latter seems less appealing than the first. Yet another idea would be to require at least the availability of the C-library at destruction time, but require that the destructor must not access any thread specific (i.e. boost thread) data. Someone in this list has pointed out the existence of a TLS destructor list in the PE header of executables. I have digged into this a little. While current compilers do not yet make use of this field it still would not answer all questions. (Perhaps that is the reason why they are not currently supporting it?) However this destructor list would need to be called by whichever library has created global objects. (Normally this is the C/C++ runtime stub.) It definitely cannot be the resonsibility of the operating system to call this list (at least in my opinion). Wrapping it up: Having the C/C++ runtime available at thread exit seems desirable to me. Calling the exithandler from the DLL (THREAD_DETACH) is too late. Calling the exit handler from within _endthread seems desirable (and can be reasonably expected to be supported by compilers one time.) Fortunately there is a chance to trick the _endthread to call arbitrary exit functions by making use of the fp-init/deinit hook. I will try to provide example code, but also post this at the same time to get your thoughts about this. Roland