src/include/Makefile.am: avoid potential file corruption

It is possible that construct_dictionary.py will be invoked twice
simultaneously, which *could* lead to file corruption of the generated
files (it probably won't, but it could).  Force "make" to serialize
the generation of the targets in this makefile, which avoids the
problem.

See lengthy comment in Makefile.am for more details.

Signed-off-by: Jeff Squyres <[email protected]>

Author: jsquyres

src/include/Makefile.am

@@ -11,7 +11,7 @@
 # Copyright (c) 2004-2005 The Regents of the University of California.
 #                         All rights reserved.
 # Copyright (c) 2013-2020 Intel, Inc.  All rights reserved.
-# Copyright (c) 2007-2020 Cisco Systems, Inc.  All rights reserved
+# Copyright (c) 2007-2022 Cisco Systems, Inc.  All rights reserved
 # Copyright (c) 2017      Research Organization for Information Science
 #                         and Technology (RIST). All rights reserved.
 # Copyright (c) 2021-2022 Nanook Consulting  All rights reserved.
@@ -23,6 +23,25 @@
 # $HEADER$
 #
 
+# The Automake BUILT_SOURCES hook ultimately calls
+# construct_dictionary.py to generate both pmix_dictionary.h and
+# pmix_dictionary.c.  However, in a parallel "make" invocation, this
+# script could be executed twice simultaneously, which *could* lead to
+# the generated pmix_dictionary.* files being corrupted (i.e., two
+# invokcations simultaneously writing to these generated files).  To
+# prevent that from happening, force this one Makefile to be run
+# serially via the .NOTPARALLEL target.  This has two side-effects:
+#
+# 1. construct_dictionary.py will only be invokved once, because since
+#    both targets are created in the first invocation, make won't need
+#    to invoke it a second time for the second target.  This is both
+#    expected and good.
+# 2. There is a (very) minor performance implication for the
+#    other make steps in this Makefile.am (i.e., they won't be run in
+#    parallel).  But this simple solution to avoid a devious potential
+#    file corruption issue is an acceptable tradeoff.
+.NOTPARALLEL:
+
 AM_CFLAGS = \
             -DPMIX_PROXY_VERSION_STRING="\"@PMIX_VERSION@\"" \
             -DPMIX_PROXY_BUGREPORT_STRING="\"@PMIX_PROXY_BUGREPORT_STRING@\""