From 5e1e92626c1e07834eb6cdb3d57623c30bf50212 Mon Sep 17 00:00:00 2001
From: Max Kellermann <max@duempel.org>
Date: Tue, 18 Feb 2014 19:13:50 +0100
Subject: [PATCH] event/SignalMonitor: unblock signals after fork

Fixes hanging child process in the "pipe" output plugin.
---
 NEWS                        |  2 ++
 src/event/SignalMonitor.cxx | 23 ++++++++++++++++++++++-
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/NEWS b/NEWS
index f12530e60..df6b14373 100644
--- a/NEWS
+++ b/NEWS
@@ -3,6 +3,8 @@ ver 0.18.9 (not yet released)
   - vorbis: fix linker failure when libvorbis/libogg are static
 * encoder
   - vorbis: fix another linker failure
+* output
+  - pipe: fix hanging child process due to blocked signals
 
 ver 0.18.8 (2014/02/07)
 * decoder
diff --git a/src/event/SignalMonitor.cxx b/src/event/SignalMonitor.cxx
index 8c8527a77..eda52aba1 100644
--- a/src/event/SignalMonitor.cxx
+++ b/src/event/SignalMonitor.cxx
@@ -39,6 +39,10 @@
 
 #include <algorithm>
 
+#ifdef USE_SIGNALFD
+#include <pthread.h>
+#endif
+
 class SignalMonitor final : private SocketMonitor {
 #ifdef USE_SIGNALFD
 	SignalFD fd;
@@ -99,7 +103,21 @@ static std::atomic_bool signal_pending[MAX_SIGNAL];
 
 static Manual<SignalMonitor> monitor;
 
-#ifndef USE_SIGNALFD
+#ifdef USE_SIGNALFD
+
+/**
+ * This is a pthread_atfork() callback that unblocks the signals that
+ * were blocked for our signalfd().  Without this, our child processes
+ * would inherit the blocked signals.
+ */
+static void
+at_fork_child()
+{
+	sigprocmask(SIG_UNBLOCK, &signal_mask, nullptr);
+}
+
+#else
+
 static void
 SignalCallback(int signo)
 {
@@ -108,6 +126,7 @@ SignalCallback(int signo)
 	if (!signal_pending[signo].exchange(true))
 		monitor->WakeUp();
 }
+
 #endif
 
 void
@@ -115,6 +134,8 @@ SignalMonitorInit(EventLoop &loop)
 {
 #ifdef USE_SIGNALFD
 	sigemptyset(&signal_mask);
+
+	pthread_atfork(nullptr, nullptr, at_fork_child);
 #endif
 
 	monitor.Construct(loop);