Hi all, I recently merged the "errno-again" branch. This branch moves the reading/saving of errno (and on Windows Get/SetLastError) closer to the actual function call. It should avoid bugs about rarely getting the wrong value for errno, in case "something special" happened: for example, it was not impossible that a call to malloc would invoke the GC at precisely the wrong spot, which might need to ask the OS for more memory, which would overwrite the current value of errno. The bug actually showed up on the Windows buildbots for GetLastError(), which would in some cases incorrectly return 0 just if the code happened to be JIT-traced (not before and not after). This is now fixed. It means any RPython project needs to be updated when it upgrades to the trunk version of the RPython translation toolchain. The fix is rather mechanical. Replace rposix.get_errno() with rposix.get_saved_errno(). Importantly, review each place that you change. You need to make sure which external function call is done before (usually in the few lines before). Once you're sure which function's errno is being checked, go to the declaration of that function, which should be using rffi.llexternal(). Add the keyword argument "save_err=rffi.RFFI_SAVE_ERRNO". This forces errno to be saved immediately after the function call, into the so-called "saved errno". This "saved errno" is another thread-local variable, which rposix.get_saved_errno() returns. Similarly with rwin32.GetLastValue() -> rwin32.GetLastValue_saved() + rffi.RFFI_SAVE_LASTERROR. If there are cases with rposix.set_errno(0), they can be killed and the following function given the flag "RFFI_ZERO_ERRNO_BEFORE". See the new docstrings of the rposix.get/set_saved_errno() and rwin32.Get/SetLastValue_saved() for more details. A bientôt, Armin.