Hi, Mikael Djurfeldt <mik...@djurfeldt.com> skribis:
> system* temporarily re-binds signal handlers to prevent the child process > from killing the parent. Thus, it is not thread safe with regard to SIGINT > (or SIGQUIT if available). So, your code has a race condition with respect > to the signal handler. This common resource can, in principle, be handled > the usual way by, for example, utilizing a mutex: [...] > I'm leaving this bug open. *Should* system* re-bind the signal handlers? > Should it really protect itself from the child? If so, we should probably > document this behaviour in the reference manual. Unless I’m mistaken, we can remove the ‘scm_dynwind_sigaction’ calls from ‘scm_system_star’: now that we use ‘posix_spawn’, this is all taken care of. This can be seen by running: strace -o /tmp/log.strace -f guile -c '(system* "/bin/sh" "-c" "echo foo $$")' … which shows pre-fork signal blocking (this is ‘internal_signal_block_all’ in spawni.c in glibc) followed, in the child (PID 28592 here), by a long series of ‘sigaction’ calls to reset handlers to their default behavior: --8<---------------cut here---------------start------------->8--- 28586 rt_sigprocmask(SIG_BLOCK, ~[], [], 8) = 0 28586 clone3({flags=CLONE_VM|CLONE_VFORK, exit_signal=SIGCHLD, stack=0x7f73b39b2000, stack_size=0x9000}, 88 <unfinished ...> 28592 rt_sigprocmask(SIG_BLOCK, NULL, ~[KILL STOP], 8) = 0 28592 rt_sigaction(SIGHUP, NULL, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=0}, 8) = 0 28592 rt_sigaction(SIGHUP, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=SA_RESTORER, sa_restorer=0x7f73b432d2a0}, NULL, 8) = 0 28592 rt_sigaction(SIGINT, NULL, {sa_handler=SIG_IGN, sa_mask=[], sa_flags=SA_RESTORER, sa_restorer=0x7f73b432d2a0}, 8) = 0 28592 rt_sigaction(SIGQUIT, NULL, {sa_handler=SIG_IGN, sa_mask=[], sa_flags=SA_RESTORER, sa_restorer=0x7f73b432d2a0}, 8) = 0 28592 rt_sigaction(SIGILL, NULL, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=0}, 8) = 0 28592 rt_sigaction(SIGILL, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=SA_RESTORER, sa_restorer=0x7f73b432d2a0}, NULL, 8) = 0 28592 rt_sigaction(SIGTRAP, NULL, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=0}, 8) = 0 28592 rt_sigaction(SIGTRAP, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=SA_RESTORER, sa_restorer=0x7f73b432d2a0}, NULL, 8) = 0 --8<---------------cut here---------------end--------------->8--- Josselin, can you confirm? Thanks, Ludo’.