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Cygwin: select: revamp non-polling code for signalfd

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Rather than waiting for signalfd_select_wait in a thread, which is racy,
create a global event "my_pendingsigs_evt" which is set and reset by
wait_sig depending only on the fact if blocked signals are pending or not.

This in turn allows to WFMO on this event in select as soon as signalfds
are present in the read descriptor set.  Select's peek and verify
will then check if one of the present signalfds is affected.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
This commit is contained in:
Corinna Vinschen
2019-08-16 16:36:06 +02:00
parent b7399d5e6f
commit 7097b05eda
8 changed files with 40 additions and 111 deletions
Download Patch File Download Diff File Expand all files Collapse all files

80
winsup/cygwin/select.cc
View File

@@ -1849,80 +1849,6 @@ fhandler_windows::select_except (select_stuff *ss)
return s;
}
static int start_thread_signalfd (select_record *, select_stuff *);
static DWORD WINAPI
thread_signalfd (void *arg)
{
select_signalfd_info *si = (select_signalfd_info *) arg;
bool event = false;
while (!event)
{
sigset_t set = 0;
_cygtls *tls = si->start->tls;
for (select_record *s = si->start; (s = s->next); )
if (s->startup == start_thread_signalfd)
set |= ((fhandler_signalfd *) s->fh)->get_sigset ();
set_signal_mask (tls->sigwait_mask, set);
tls->signalfd_select_wait = si->evt;
sig_dispatch_pending (true);
switch (WaitForSingleObject (si->evt, INFINITE))
{
case WAIT_OBJECT_0:
tls->signalfd_select_wait = NULL;
event = true;
break;
default:
break;
}
if (si->stop_thread)
break;
if (!event)
Sleep (1L);
}
CloseHandle (si->evt);
return 0;
}
static int
start_thread_signalfd (select_record *me, select_stuff *stuff)
{
select_signalfd_info *si;
if ((si = stuff->device_specific_signalfd))
{
me->h = *si->thread;
return 1;
}
si = new select_signalfd_info;
si->start = &stuff->start;
si->stop_thread = false;
si->evt = CreateEventW (&sec_none_nih, TRUE, FALSE, NULL);
si->thread = new cygthread (thread_signalfd, si, "signalfdsel");
me->h = *si->thread;
stuff->device_specific_signalfd = si;
return 1;
}
static void
signalfd_cleanup (select_record *, select_stuff *stuff)
{
select_signalfd_info *si;
if (!(si = stuff->device_specific_signalfd))
return;
if (si->thread)
{
si->stop_thread = true;
SetEvent (si->evt);
si->thread->detach ();
}
delete si;
stuff->device_specific_signalfd = NULL;
}
static int
peek_signalfd (select_record *me, bool)
{
@@ -1942,17 +1868,19 @@ verify_signalfd (select_record *me, fd_set *rfds, fd_set *wfds, fd_set *efds)
return peek_signalfd (me, true);
}
extern HANDLE my_pendingsigs_evt;
select_record *
fhandler_signalfd::select_read (select_stuff *stuff)
{
select_record *s = stuff->start.next;
if (!s->startup)
{
s->startup = start_thread_signalfd;
s->startup = no_startup;
s->verify = verify_signalfd;
s->cleanup = signalfd_cleanup;
}
s->peek = peek_signalfd;
s->h = my_pendingsigs_evt; /* wait_sig sets this if signal are pending */
s->read_selected = true;
s->read_ready = false;
return s;