ds: flatten + reuse @events, epoll_wait style fixes

Consistently returning the equivalent of pollfd.revents in a
portable manner was never worth the effort for us, as we use the
same ->event_step callback regardless of POLLIN/POLLOUT/POLLHUP.

Being a Perl, @events knows it size and we don't have to return
a maximum index for the caller to iterate on.

We can also avoid redundant integer coercion ("+0") since we
ensure everything is an IV in other places.

Finally, vec() is preferable to ("\0" x $size) for resizing
buffers because it only needs to write the extended portion
and not overwrite the entire buffer.

1 files changed, 37 insertions, 29 deletions

diff --git a/lib/PublicInbox/Syscall.pm b/lib/PublicInbox/Syscall.pm
index e4f00a2a..c403f78a 100644
--- a/lib/PublicInbox/Syscall.pm
+++ b/lib/PublicInbox/Syscall.pm
@@ -227,38 +227,46 @@ sub epoll_ctl_mod8 {
 our $epoll_wait_events;
 our $epoll_wait_size = 0;
 sub epoll_wait_mod4 {
-    # resize our static buffer if requested size is bigger than we've ever done
-    if ($_[1] > $epoll_wait_size) {
-        $epoll_wait_size = $_[1];
-        $epoll_wait_events = "\0" x 12 x $epoll_wait_size;
-    }
-    my $ct = syscall($SYS_epoll_wait, $_[0]+0, $epoll_wait_events, $_[1]+0, $_[2]+0);
-    for (0..$ct-1) {
-        @{$_[3]->[$_]}[1,0] = unpack("LL", substr($epoll_wait_events, 12*$_, 8));
-    }
-    return $ct;
+        my ($epfd, $maxevents, $timeout_msec, $events) = @_;
+        # resize our static buffer if maxevents bigger than we've ever done
+        if ($maxevents > $epoll_wait_size) {
+                $epoll_wait_size = $maxevents;
+                vec($epoll_wait_events, $maxevents * 12 * 8 - 1, 1) = 0;
+        }
+        @$events = ();
+        my $ct = syscall($SYS_epoll_wait, $epfd, $epoll_wait_events,
+                        $maxevents, $timeout_msec);
+        for (0..$ct - 1) {
+                # 12-byte struct epoll_event
+                # 4 bytes uint32_t events mask (skipped, useless to us)
+                # 8 bytes: epoll_data_t union (first 4 bytes are the fd)
+                # So we skip the first 4 bytes and take the middle 4:
+                $events->[$_] = unpack('L', substr($epoll_wait_events,
+                                                        12 * $_ + 4, 4));
+        }
 }
 
 sub epoll_wait_mod8 {
-    # resize our static buffer if requested size is bigger than we've ever done
-    if ($_[1] > $epoll_wait_size) {
-        $epoll_wait_size = $_[1];
-        $epoll_wait_events = "\0" x 16 x $epoll_wait_size;
-    }
-    my $ct;
-    if ($no_deprecated) {
-        $ct = syscall($SYS_epoll_wait, $_[0]+0, $epoll_wait_events, $_[1]+0, $_[2]+0, undef);
-    } else {
-        $ct = syscall($SYS_epoll_wait, $_[0]+0, $epoll_wait_events, $_[1]+0, $_[2]+0);
-    }
-    for (0..$ct-1) {
-        # 16 byte epoll_event structs, with format:
-        #    4 byte mask [idx 1]
-        #    4 byte padding (we put it into idx 2, useless)
-        #    8 byte data (first 4 bytes are fd, into idx 0)
-        @{$_[3]->[$_]}[1,2,0] = unpack("LLL", substr($epoll_wait_events, 16*$_, 12));
-    }
-    return $ct;
+        my ($epfd, $maxevents, $timeout_msec, $events) = @_;
+
+        # resize our static buffer if maxevents bigger than we've ever done
+        if ($maxevents > $epoll_wait_size) {
+                $epoll_wait_size = $maxevents;
+                vec($epoll_wait_events, $maxevents * 16 * 8 - 1, 1) = 0;
+        }
+        @$events = ();
+        my $ct = syscall($SYS_epoll_wait, $epfd, $epoll_wait_events,
+                        $maxevents, $timeout_msec,
+                        $no_deprecated ? undef : ());
+        for (0..$ct - 1) {
+                # 16-byte struct epoll_event
+                # 4 bytes uint32_t events mask (skipped, useless to us)
+                # 4 bytes padding (skipped, useless)
+                # 8 bytes epoll_data_t union (first 4 bytes are the fd)
+                # So skip the first 8 bytes, take 4, and ignore the last 4:
+                $events->[$_] = unpack('L', substr($epoll_wait_events,
+                                                        16 * $_ + 8, 4));
+        }
 }
 
 sub signalfd ($$$) {