On 06/01/2016 09:04 AM, Yordanov, Dimitar wrote: > I'm looking into an issue with a CMake build on Linux hanging in a > select syscall, when using EXECUTE_PROCESS without any additional > arguments. The subprocess executed is "chmod". The child finishes and > is marked as a zombie, but CMake did not realize that. The only > descriptors left open are the one of the signaling pipe.
The code in question uses a well-known idiom to make SIGCHLD select()able. It has worked well for years on many platforms. Are you running inside some kind of virtualization or emulation environment? > is the use of a shared variable "kwsysProcesses" in the signal > handler. I think the usage of non volatile shared objects should be > avoided in signal handlers and we should just do as less as we > can in there. IIRC we suppress signals while updating the shared variables. CMake also doesn't use threads. > Why do we need the "(void)pipeStatus;" lines. For debugging? Some compilers complain we don't use the return value of write(). Therefore we must assign it to a variable. Then compilers complain that the variable is assigned a value that is never used. The cast suppresses this. > Why do we need to read from the pipe in the signal handler? If many signals are received in succession before the select() wakes up and reads from the pipe then it could fill the pipe and block in the handler. We do a non-blocking read to make sure the pipe never has more than one byte in it. All we care about is waking up any blocking select(). BTW, in the long run I'd like to drop this code completely and move to libuv. Meanwhile I'd rather not spend too much time updating the existing implementation. -Brad -- Powered by www.kitware.com Please keep messages on-topic and check the CMake FAQ at: http://www.cmake.org/Wiki/CMake_FAQ Kitware offers various services to support the CMake community. For more information on each offering, please visit: CMake Support: http://cmake.org/cmake/help/support.html CMake Consulting: http://cmake.org/cmake/help/consulting.html CMake Training Courses: http://cmake.org/cmake/help/training.html Visit other Kitware open-source projects at http://www.kitware.com/opensource/opensource.html Follow this link to subscribe/unsubscribe: http://public.kitware.com/mailman/listinfo/cmake-developers
