osutil: add a function to unblock signals Signals could be blocked by something like: #include <unistd.h> #include <signal.h> int main(int argc, char * const argv[]) { sigset_t set; sigfillset(&set); sigprocmask(SIG_BLOCK, &set, NULL); execv("/bin/hg", argv); return 0; } One of the problems is if SIGCHLD is blocked, chgserver would not reap zombie workers since it depends on SIGCHLD handler entirely. While it's the parent process to blame but it seems a good idea to just unblock the signal from hg. FWIW git does that for SIGPIPE already [1]. Unfortunately Python 2 does not reset or provide APIs to change signal masks. Therefore let's add one in osutil. Note: Python 3.3 introduced `signal.pthread_sigmask` which solves the problem. `sigprocmask` is part of POSIX [2] so there is no feature testing in `setup.py`. [1]: https://github.com/git/git/commit/7559a1be8a0afb10df41d25e4cf4c5285a5faef1 [2]: http://pubs.opengroup.org/onlinepubs/7908799/xsh/sigprocmask.html Differential Revision: https://phab.mercurial-scm.org/D1736