user/dev discussion of public-inbox itself
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From: Eric Wong <e@yhbt.net>
To: meta@public-inbox.org
Subject: [PATCH 4/5] spawn: unblock SIGCHLD in subprocess
Date: Mon, 29 Jun 2020 10:34:20 +0000
Message-ID: <20200629103421.31016-5-e@yhbt.net> (raw)
In-Reply-To: <20200629103421.31016-1-e@yhbt.net>

Subprocess we spawn may want to use SIGCHLD for themselves.
This also ensures we restore default signal handlers
in the pure Perl version.
---
 lib/PublicInbox/Spawn.pm   | 11 ++++++++---
 lib/PublicInbox/SpawnPP.pm |  5 +++++
 t/spawn.t                  | 27 +++++++++++++++++++++++++++
 3 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/lib/PublicInbox/Spawn.pm b/lib/PublicInbox/Spawn.pm
index 888283d0d09..f90d8f6d3dd 100644
--- a/lib/PublicInbox/Spawn.pm
+++ b/lib/PublicInbox/Spawn.pm
@@ -78,7 +78,7 @@ int pi_fork_exec(SV *redirref, SV *file, SV *cmdref, SV *envref, SV *rlimref,
 	const char *filename = SvPV_nolen(file);
 	pid_t pid;
 	char **argv, **envp;
-	sigset_t set, old;
+	sigset_t set, old, cset;
 	int ret, perrnum, cerrnum = 0;
 
 	AV2C_COPY(argv, cmd);
@@ -88,6 +88,10 @@ int pi_fork_exec(SV *redirref, SV *file, SV *cmdref, SV *envref, SV *rlimref,
 	assert(ret == 0 && "BUG calling sigfillset");
 	ret = sigprocmask(SIG_SETMASK, &set, &old);
 	assert(ret == 0 && "BUG calling sigprocmask to block");
+	ret = sigemptyset(&cset);
+	assert(ret == 0 && "BUG calling sigemptyset");
+	ret = sigaddset(&cset, SIGCHLD);
+	assert(ret == 0 && "BUG calling sigaddset for SIGCHLD");
 	pid = vfork();
 	if (pid == 0) {
 		int sig;
@@ -120,9 +124,10 @@ int pi_fork_exec(SV *redirref, SV *file, SV *cmdref, SV *envref, SV *rlimref,
 		}
 
 		/*
-		 * don't bother unblocking, we don't want signals
-		 * to the group taking out a subprocess
+		 * don't bother unblocking other signals for now, just SIGCHLD.
+		 * we don't want signals to the group taking out a subprocess
 		 */
+		(void)sigprocmask(SIG_UNBLOCK, &cset, NULL);
 		execve(filename, argv, envp);
 		exit_err(&cerrnum);
 	}
diff --git a/lib/PublicInbox/SpawnPP.pm b/lib/PublicInbox/SpawnPP.pm
index 34ce2052c60..a72d5a2d86f 100644
--- a/lib/PublicInbox/SpawnPP.pm
+++ b/lib/PublicInbox/SpawnPP.pm
@@ -36,6 +36,11 @@ sub pi_fork_exec ($$$$$$) {
 		if ($cd ne '') {
 			chdir $cd or die "chdir $cd: $!";
 		}
+		$SIG{$_} = 'DEFAULT' for keys %SIG;
+		my $cset = POSIX::SigSet->new();
+		$cset->addset(POSIX::SIGCHLD) or die "can't add SIGCHLD: $!";
+		sigprocmask(SIG_UNBLOCK, $cset) or
+					die "can't unblock SIGCHLD: $!";
 		if ($ENV{MOD_PERL}) {
 			exec which('env'), '-i', @$env, @$cmd;
 			die "exec env -i ... $cmd->[0] failed: $!\n";
diff --git a/t/spawn.t b/t/spawn.t
index 44355f43655..fd669e222e1 100644
--- a/t/spawn.t
+++ b/t/spawn.t
@@ -4,6 +4,7 @@ use strict;
 use warnings;
 use Test::More;
 use PublicInbox::Spawn qw(which spawn popen_rd);
+use PublicInbox::Sigfd;
 
 {
 	my $true = which('true');
@@ -17,6 +18,32 @@ use PublicInbox::Spawn qw(which spawn popen_rd);
 	is($?, 0, 'true exited successfully');
 }
 
+{ # ensure waitpid(-1, 0) and SIGCHLD works in spawned process
+	my $script = <<'EOF';
+$| = 1; # unbuffer stdout
+defined(my $pid = fork) or die "fork: $!";
+if ($pid == 0) { exit }
+elsif ($pid > 0) {
+	my $waited = waitpid(-1, 0);
+	$waited == $pid or die "mismatched child $pid != $waited";
+	$? == 0 or die "child err: $>";
+	$SIG{CHLD} = sub { print "HI\n"; exit };
+	print "RDY $$\n";
+	sleep while 1;
+}
+EOF
+	my $oldset = PublicInbox::Sigfd::block_signals();
+	my $rd = popen_rd([$^X, '-e', $script]);
+	diag 'waiting for child to reap grandchild...';
+	chomp(my $line = readline($rd));
+	my ($rdy, $pid) = split(' ', $line);
+	is($rdy, 'RDY', 'got ready signal, waitpid(-1) works in child');
+	ok(kill('CHLD', $pid), 'sent SIGCHLD to child');
+	is(readline($rd), "HI\n", '$SIG{CHLD} works in child');
+	ok(close $rd, 'popen_rd close works');
+	PublicInbox::Sigfd::sig_setmask($oldset);
+}
+
 {
 	my ($r, $w);
 	pipe $r, $w or die "pipe failed: $!";

  parent reply index

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-27 10:03 [PATCH 00/34] watch: add IMAP and NNTP support Eric Wong
2020-06-27 10:03 ` [PATCH 01/34] inboxwritable: ensure ssoma.lock exists on init Eric Wong
2020-06-27 10:03 ` [PATCH 02/34] inbox: warn on ->on_inbox_unlock exception Eric Wong
2020-06-27 10:03 ` [PATCH 03/34] IMAPTracker: Add a helper to track our place in reading imap mailboxes Eric Wong
2020-06-27 10:03 ` [PATCH 04/34] imaptracker: use ~/.local/share/public-inbox/imap.sqlite3 Eric Wong
2020-06-27 10:03 ` [PATCH 05/34] watchmaildir: hoist out compile_watchheaders Eric Wong
2020-06-27 10:03 ` [PATCH 06/34] watchmaildir: fix check for spam vs ham inbox conflicts Eric Wong
2020-06-27 10:03 ` [PATCH 07/34] URI IMAP support Eric Wong
2020-06-27 10:03 ` [PATCH 08/34] watch: preliminary " Eric Wong
2020-06-27 10:03 ` [PATCH 09/34] kqnotify|fake_inotify: detect Maildir write ops Eric Wong
2020-06-27 10:03 ` [PATCH 10/34] watch: remove Filesys::Notify::Simple dependency Eric Wong
2020-06-27 10:03 ` [PATCH 11/34] watch: use signalfd for Maildir watching Eric Wong
2020-06-27 19:05   ` Kyle Meyer
2020-06-27 22:32     ` Eric Wong
2020-06-27 10:03 ` [PATCH 12/34] ds: remove fields.pm usage Eric Wong
2020-06-27 10:03 ` [PATCH 13/34] watch: wire up IMAP IDLE reapers to DS Eric Wong
2020-06-27 10:03 ` [PATCH 14/34] watch: support IMAP polling Eric Wong
2020-06-27 10:03 ` [PATCH 15/34] config: support ->urlmatch method for -watch Eric Wong
2020-06-27 10:03 ` [PATCH 16/34] watch: stop importers before forking Eric Wong
2020-06-27 10:03 ` [PATCH 17/34] watch: use UID SEARCH to avoid empty UID FETCH Eric Wong
2020-06-27 10:03 ` [PATCH 18/34] ds: add_timer: allow passing arg to callback Eric Wong
2020-06-27 10:03 ` [PATCH 19/34] imaptracker: add {url} field to reduce args Eric Wong
2020-06-27 10:03 ` [PATCH 20/34] imaptracker: drop {dbname} field Eric Wong
2020-06-27 10:03 ` [PATCH 21/34] watch: avoid long transaction to IMAPTracker Eric Wong
2020-06-27 10:03 ` [PATCH 22/34] watch: support imap.fetchBatchSize parameter Eric Wong
2020-06-27 10:03 ` [PATCH 23/34] watch: imap: be quiet about disconnecting on quit Eric Wong
2020-06-27 10:03 ` [PATCH 24/34] watch: support multiple watch: directives per-inbox Eric Wong
2020-06-27 10:03 ` [PATCH 25/34] watch: remove {mdir} array Eric Wong
2020-06-27 10:03 ` [PATCH 26/34] watch: just use ->urlmatch Eric Wong
2020-06-27 10:03 ` [PATCH 27/34] testcommon: $ENV{TAIL} supports non-@ARGV redirects Eric Wong
2020-06-27 10:03 ` [PATCH 28/34] watch: add NNTP support Eric Wong
2020-06-27 19:06   ` Kyle Meyer
2020-06-27 10:03 ` [PATCH 29/34] watch: show user-specified URL consistently Eric Wong
2020-06-27 10:03 ` [PATCH 30/34] watch: enable autoflush for STDOUT and STDERR Eric Wong
2020-06-27 10:03 ` [PATCH 31/34] watch: use our own "git credential" wrapper Eric Wong
2020-06-27 10:03 ` [PATCH 32/34] watch: support ~/.netrc via Net::Netrc Eric Wong
2020-06-27 10:03 ` [PATCH 33/34] imaptracker: use flock(2) around writes Eric Wong
2020-06-27 10:04 ` [PATCH 34/34] watch: simplify internal structures Eric Wong
2020-06-29 10:34 ` [PATCH 0/5] watch: Maildir fixes Eric Wong
2020-06-29 10:34   ` [PATCH 1/5] watch: check for duplicates in ->over before spamcheck Eric Wong
2020-06-29 10:34   ` [PATCH 2/5] watch: show path for warnings from spam messages Eric Wong
2020-06-29 10:34   ` [PATCH 3/5] watch: ensure SIGCHLD works in forked children Eric Wong
2020-06-29 10:34   ` Eric Wong [this message]
2020-07-07  6:17     ` [PATCH 6/5] t/spawn: fix test reliability Eric Wong
2020-06-29 10:34   ` [PATCH 5/5] watch: make waitpid() synchronous for Maildir scans Eric Wong
2020-06-29 10:37     ` Eric Wong

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