testcommon: speed up wait_for_tail() on GNU/Linux

Somewhat recent versions of GNU tail(1) use inotify(7) on Linux;
so don't penalize hackers using TAIL='tail -F' to run their tests
with extra delays.

Ironically, we still need to busy loop on /proc/$TAIL_PID/{fd,fdinfo}
since inotify doesn't seem to support procfs.

1 files changed, 38 insertions, 5 deletions

diff --git a/lib/PublicInbox/TestCommon.pm b/lib/PublicInbox/TestCommon.pm
index 79e597f5..246047b1 100644
--- a/lib/PublicInbox/TestCommon.pm
+++ b/lib/PublicInbox/TestCommon.pm
@@ -5,6 +5,7 @@
 package PublicInbox::TestCommon;
 use strict;
 use parent qw(Exporter);
+use v5.10.1;
 use Fcntl qw(FD_CLOEXEC F_SETFD F_GETFD :seek);
 use POSIX qw(dup2);
 use IO::Socket::INET;
@@ -249,7 +250,39 @@ sub run_script ($;$$) {
         $? == 0;
 }
 
-sub wait_for_tail () { sleep(2) }
+sub tick (;$) {
+        my $tick = shift // 0.1;
+        select undef, undef, undef, $tick;
+        1;
+}
+
+sub wait_for_tail ($;$) {
+        my ($tail_pid, $stop) = @_;
+        my $wait = 2;
+        if ($^O eq 'linux') { # GNU tail may use inotify
+                state $tail_has_inotify;
+                return tick if $stop && $tail_has_inotify;
+                my $end = time + $wait;
+                my @ino;
+                do {
+                        @ino = grep {
+                                readlink($_) =~ /\binotify\b/
+                        } glob("/proc/$tail_pid/fd/*");
+                } while (!@ino && time <= $end and tick);
+                return if !@ino;
+                $tail_has_inotify = 1;
+                $ino[0] =~ s!/fd/!/fdinfo/!;
+                my @info;
+                do {
+                        if (open my $fh, '<', $ino[0]) {
+                                local $/ = "\n";
+                                @info = grep(/^inotify wd:/, <$fh>);
+                        }
+                } while (scalar(@info) < 2 && time <= $end and tick);
+        } else {
+                sleep($wait);
+        }
+}
 
 # like system() built-in, but uses spawn() for env/rdr + vfork
 sub xsys {
@@ -294,7 +327,7 @@ sub start_script {
                                 exec(split(' ', $tail_cmd), @paths);
                                 die "$tail_cmd failed: $!";
                         }
-                        wait_for_tail();
+                        wait_for_tail($tail_pid);
                 }
         }
         defined(my $pid = fork) or die "fork: $!\n";
@@ -359,9 +392,9 @@ sub join {
 sub DESTROY {
         my ($self) = @_;
         return if $self->{owner} != $$;
-        if (my $tail = delete $self->{tail_pid}) {
-                PublicInbox::TestCommon::wait_for_tail();
-                CORE::kill('TERM', $tail);
+        if (my $tail_pid = delete $self->{tail_pid}) {
+                PublicInbox::TestCommon::wait_for_tail($tail_pid, 1);
+                CORE::kill('TERM', $tail_pid);
         }
         $self->join('TERM');
 }