From d880550d56911af6fdba25b4863bc8e49d4df29f Mon Sep 17 00:00:00 2001
From: neumann <neumann>
Date: Tue, 25 Jul 2023 09:01:51 +0000
Subject: Prefer vfork() over posix_spawnp()

In essence, older versions of the posix_spawn(p) implementation under
glibc have the problem not returning the correct error number in case
the spawn call fails. This is e.g. a problem with CentOS 7, which uses
GNU libc 2.17, which was released 2012-12-25. This has the consequence
that on such systems, Tcl is not error message compliant to versions
without posix_spawn.

The versions of vfork() do not face this problem and show similar
performance characteristics like with posix_spawnp() (spawn time in
essence independent of memory footprint size).

This change was tested with macOS 13.4, Ubuntu 20.04, CentOS 7.9 and
OpenBSD 7.2.
---
 unix/tcl.m4        |  1 +
 unix/tclUnixPort.h | 14 ++++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/unix/tcl.m4 b/unix/tcl.m4
index dfa812b..9d2c38c 100644
--- a/unix/tcl.m4
+++ b/unix/tcl.m4
@@ -2069,6 +2069,7 @@ dnl # preprocessing tests use only CPPFLAGS.
 
     # Check for posix_spawnp() and friends unconditionally
     AC_CHECK_FUNCS(posix_spawnp posix_spawn_file_actions_adddup2 posix_spawnattr_setflags)
+    AC_CHECK_FUNCS([vfork])
 
     # FIXME: This subst was left in only because the TCL_DL_LIBS
     # entry in tclConfig.sh uses it. It is not clear why someone
diff --git a/unix/tclUnixPort.h b/unix/tclUnixPort.h
index c2115df..ea4beac 100644
--- a/unix/tclUnixPort.h
+++ b/unix/tclUnixPort.h
@@ -636,6 +636,20 @@ extern char **		environ;
 	    defined(HAVE_WEAK_IMPORT) && MAC_OS_X_VERSION_MIN_REQUIRED < 1050
 #	warning "Weak import of 64-bit CoreFoundation is not supported, will not run on Mac OS X < 10.5."
 #   endif
+#   if defined(HAVE_POSIX_SPAWNP)
+/*
+ * Under macOS, test exec-17.1 fails (I/O setup after closing stdout) with
+ * posix_spawnp(), but the classic implementation (based on fork()+execvp())
+ * works without the severe performance implications with large memory 
+ * footprints. So, deactivate HAVE_POSIX_SPAWNP
+ */
+#       undef HAVE_POSIX_SPAWNP
+#   endif
+#else
+#  if defined(HAVE_POSIX_SPAWNP) && defined(HAVE_VFORK)
+#       define USE_VFORK
+#       undef HAVE_POSIX_SPAWNP
+#  endif
 #endif /* __APPLE__ */
 
 /*
-- 
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