Hi I am tracking portability problems in syncio.c. It maks heavy usage of swapcontext(), which is something not recommanded (it was removed from the 2008 edition of POSIX.1). As I understand, syntask_wrap() has the problem of retreiving the task. The parameter padded by makecontext() is not reliable, since the standard does not specify the type of the argument. Passing a pointer on an LP64 machine is doomed to fail if the par ameter is taken as an int by the implementation. Therefore the author of the code used thread specific storage to pass the task ,through synctask_set() / syntask_get(). I encounter crashes because syntask_get() in syntask_wrap() gets NULL, or even get a value different than the one synctask_set() gets as its argument. Using synctask_set() argument tend to be much more reliable at mine than trusting syntask_get(). Logging pthread_self() and task in synctask_new(), syntask_switchto() and synctask_wrap, I can see the reason why it fails: syntask_switchto() / syntask_set() is sometimes done in a different thread that the one where synctask_wrap resumes. I suspect we fall into unspecified behavior with thread and swapcontext() interractions. Given that swapcontext() is not standard anymore, this would not be very suprising. I try to think about a workaround of the problem. An idea would be to store something specific to the context, like stack address, in struct synctask. syntask_wrap() could retreive the task by looking up its own stack address with getcontext() and search a matching task in a global list of tasks. I am not sure this is leading anywhere, though. -- Emmanuel Dreyfus manu@xxxxxxxxxx
