From 83e9b5763245c727993eab0a0133b2b337605f88 Mon Sep 17 00:00:00 2001
From: Martin Panter <vadmium+py@gmail.com>
Date: Wed, 3 Feb 2016 05:19:44 +0000
Subject: Issue #24421: Compile _math.c separately to avoid race condition

---
 Makefile.pre.in |  6 +++++-
 Misc/NEWS       |  4 ++++
 setup.py        | 12 ++++++++----
 3 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/Makefile.pre.in b/Makefile.pre.in
index 3b43f1b..cf9bec3 100644
--- a/Makefile.pre.in
+++ b/Makefile.pre.in
@@ -528,11 +528,15 @@ pybuilddir.txt: $(BUILDPYTHON)
 		exit 1 ; \
 	fi
 
+# This is shared by the math and cmath modules
+Modules/_math.o: Modules/_math.c Modules/_math.h
+	$(CC) -c $(CCSHARED) $(PY_CFLAGS) -o $@ $<
+
 # Build the shared modules
 # Under GNU make, MAKEFLAGS are sorted and normalized; the 's' for
 # -s, --silent or --quiet is always the first char.
 # Under BSD make, MAKEFLAGS might be " -s -v x=y".
-sharedmods: $(BUILDPYTHON) pybuilddir.txt
+sharedmods: $(BUILDPYTHON) pybuilddir.txt Modules/_math.o
 	@case "$$MAKEFLAGS" in \
 	    *\ -s*|s*) quiet="-q";; \
 	    *) quiet="";; \
diff --git a/Misc/NEWS b/Misc/NEWS
index 10eee93..49d3fd1 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -143,6 +143,10 @@ Tests
 Build
 -----
 
+- Issue #24421: Compile Modules/_math.c once, before building extensions.
+  Previously it could fail to compile properly if the math and cmath builds
+  were concurrent.
+
 - Issue #25824: Fixes sys.winver to not include any architecture suffix.
 
 - Issue #25348: Added ``--pgo`` and ``--pgo-job`` arguments to
diff --git a/setup.py b/setup.py
index 0943188..780889f 100644
--- a/setup.py
+++ b/setup.py
@@ -584,13 +584,17 @@ class PyBuildExt(build_ext):
 
         # array objects
         exts.append( Extension('array', ['arraymodule.c']) )
+
+        shared_math = 'Modules/_math.o'
         # complex math library functions
-        exts.append( Extension('cmath', ['cmathmodule.c', '_math.c'],
-                               depends=['_math.h'],
+        exts.append( Extension('cmath', ['cmathmodule.c'],
+                               extra_objects=[shared_math],
+                               depends=['_math.h', shared_math],
                                libraries=math_libs) )
         # math library functions, e.g. sin()
-        exts.append( Extension('math',  ['mathmodule.c', '_math.c'],
-                               depends=['_math.h'],
+        exts.append( Extension('math',  ['mathmodule.c'],
+                               extra_objects=[shared_math],
+                               depends=['_math.h', shared_math],
                                libraries=math_libs) )
         # fast string operations implemented in C
         exts.append( Extension('strop', ['stropmodule.c']) )
-- 
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