Jonathan Biggar wrote:
Angus Leeming wrote:
namespace {
std::map<pid_t, int> completed_children;
int status; sig_atomic_t pid;
}
extern "C" void child_handler(int) { pid = wait(&status); std::map<pid_t, int>::iterator it = completed_children.find(pid); if (it != completed_children.end()) it->second = status; }
I'm pretty sure that the above is safe code. It does the absolute minimum in the handler routine. wait() is guaranteed to be async-safe. Moreover, the handler receives only SIGCHLD signals and so cannot receive multiple calls simultaneaously. However, I'm unsure whether it Ok to search the map like this. Any advice?
That's not safe code, since the child_handler() function could be called at any time, interrupting other code that is modifying the completed_children map.
Yes, I've thought of that. We just need to block any signals when we're modifying the map: unix_reaper::unix_reaper() { signal(SIGCHLD, boost_child_handler); sigemptyset(&old_mask_); sigemptyset(&new_mask_); sigaddset(&new_mask_, SIGCHLD); } void unix_reaper::register(pid_t pid) { // Block the SIGCHLD signal. sigprocmask(SIG_BLOCK, &new_mask_, &old_mask_); // This is the map. children_[pid] = -1; // Unblock the SIGCHLD signal and restore the old mask. sigprocmask(SIG_SETMASK, &old_mask_, 0); } Does this address your concern? Angus