From 2b02747ec56d601124a37c3992d4bd1fe3ef4881 Mon Sep 17 00:00:00 2001
From: Vojtech Bubnik <bubnikv@gmail.com>
Date: Thu, 7 Jan 2021 19:14:48 +0100
Subject: [PATCH] On OSX, we use boost::process::spawn() to launch new
 instances of PrusaSlicer from another PrusaSlicer. boost::process::spawn()
 sets SIGCHLD to SIGIGN for the child process, thus if a child PrusaSlicer
 spawns another subprocess and the subrocess dies, the child PrusaSlicer will
 not receive information on end of subprocess (posix waitpid() call will
 always fail). https://jmmv.dev/2008/10/boostprocess-and-sigchld.html The
 child instance of PrusaSlicer has to reset SIGCHLD to its default, so that
 posix waitpid() and similar continue to work. Fixes #5507

---
 src/slic3r/GUI/GUI_Init.cpp  | 15 +++++++++++++++
 src/slic3r/Utils/Process.cpp | 12 ++++++------
 2 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/src/slic3r/GUI/GUI_Init.cpp b/src/slic3r/GUI/GUI_Init.cpp
index 70536c6ba..839782741 100644
--- a/src/slic3r/GUI/GUI_Init.cpp
+++ b/src/slic3r/GUI/GUI_Init.cpp
@@ -16,11 +16,26 @@
 #include <boost/nowide/iostream.hpp>
 #include <boost/nowide/convert.hpp>
 
+#if __APPLE__
+    #include <signal.h>
+#endif // __APPLE__
+
 namespace Slic3r {
 namespace GUI {
 
 int GUI_Run(GUI_InitParams &params)
 {
+#if __APPLE__
+    // On OSX, we use boost::process::spawn() to launch new instances of PrusaSlicer from another PrusaSlicer.
+    // boost::process::spawn() sets SIGCHLD to SIGIGN for the child process, thus if a child PrusaSlicer spawns another
+    // subprocess and the subrocess dies, the child PrusaSlicer will not receive information on end of subprocess
+    // (posix waitpid() call will always fail).
+    // https://jmmv.dev/2008/10/boostprocess-and-sigchld.html
+    // The child instance of PrusaSlicer has to reset SIGCHLD to its default, so that posix waitpid() and similar continue to work.
+    // See GH issue #5507
+    signal(SIGCHLD, SIG_DFL);
+#endif // __APPLE__
+
     try {
         GUI::GUI_App* gui = new GUI::GUI_App(params.start_as_gcodeviewer ? GUI::GUI_App::EAppMode::GCodeViewer : GUI::GUI_App::EAppMode::Editor);
         if (gui->get_app_mode() != GUI::GUI_App::EAppMode::GCodeViewer) {
diff --git a/src/slic3r/Utils/Process.cpp b/src/slic3r/Utils/Process.cpp
index 1199e5e76..a8fc59f52 100644
--- a/src/slic3r/Utils/Process.cpp
+++ b/src/slic3r/Utils/Process.cpp
@@ -17,7 +17,6 @@
 // For starting another PrusaSlicer instance on OSX.
 // Fails to compile on Windows on the build server.
 #ifdef __APPLE__
-	#include <signal.h>
     #include <boost/process/spawn.hpp>
     #include <boost/process/args.hpp>
 #endif
@@ -79,11 +78,12 @@ static void start_new_slicer_or_gcodeviewer(const NewSlicerInstanceType instance
 			if (instance_type == NewSlicerInstanceType::Slicer && single_instance)
 				args.emplace_back("--single-instance");
 			boost::process::spawn(bin_path, args);
-			// boost::process::spawn() sets SIGINT to SIGIGN, which collides with boost::process waiting for a child to finish!
-			// https://jmmv.dev/2008/10/boostprocess-and-sigchld.html
-			// Thus reset the SIGINT to its default, so that posix waitpid() and similar continue to work.
-			// Fixes Crash on Eject in Second Instance on macOS #5507
-			signal(SIGINT, SIG_DFL);
+		    // boost::process::spawn() sets SIGCHLD to SIGIGN for the child process, thus if a child PrusaSlicer spawns another
+		    // subprocess and the subrocess dies, the child PrusaSlicer will not receive information on end of subprocess
+		    // (posix waitpid() call will always fail).
+		    // https://jmmv.dev/2008/10/boostprocess-and-sigchld.html
+		    // The child instance of PrusaSlicer has to reset SIGCHLD to its default, so that posix waitpid() and similar continue to work.
+		    // See GH issue #5507
 		}
 		catch (const std::exception& ex) {
 			BOOST_LOG_TRIVIAL(error) << "Failed to spawn a new slicer \"" << bin_path.string() << "\": " << ex.what();