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Fix improper double-fire of signal sources on Linux #279

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merged 1 commit into from
Jul 18, 2017
Merged

Fix improper double-fire of signal sources on Linux #279

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24 changes: 18 additions & 6 deletions src/event/event_epoll.c
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Original file line number Diff line number Diff line change
Expand Up @@ -467,12 +467,24 @@ _dispatch_event_merge_signal(dispatch_muxnote_t dmn)
{
dispatch_unote_linkage_t dul, dul_next;
struct signalfd_siginfo si;

dispatch_assume(read(dmn->dmn_fd, &si, sizeof(si)) == sizeof(si));

TAILQ_FOREACH_SAFE(dul, &dmn->dmn_readers_head, du_link, dul_next) {
dispatch_unote_t du = _dispatch_unote_linkage_get_unote(dul);
dux_merge_evt(du._du, EV_ADD|EV_ENABLE|EV_CLEAR, 1, 0, 0);
ssize_t rc;

// Linux has the weirdest semantics around signals: if it finds a thread
// that has not masked a process wide-signal, it may deliver it to this
// thread, meaning that the signalfd may have been made readable, but the
// signal consumed through the legacy delivery mechanism.
//
// Because of this we can get a misfire of the signalfd yielding EAGAIN the
// first time around. The _dispatch_muxnote_signal_block_and_raise() hack
// will kick in, the thread with the wrong mask will be fixed up, and the
// signal delivered to us again properly.
if ((rc = read(dmn->dmn_fd, &si, sizeof(si))) == sizeof(si)) {
TAILQ_FOREACH_SAFE(dul, &dmn->dmn_readers_head, du_link, dul_next) {
dispatch_unote_t du = _dispatch_unote_linkage_get_unote(dul);
dux_merge_evt(du._du, EV_ADD|EV_ENABLE|EV_CLEAR, 1, 0, 0);
}
} else {
dispatch_assume(rc == -1 && errno == EAGAIN);
}
}

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