build: cautiously allow parallel builds.

Over two years ago, I disabled parallel building with a
.NOTPARALLEL: directive in the Makefile, due to some rules
that depended on order of updates of their prerequisites.

Today the situation is better. It looks like there are just a
few rules that have to be fixed, all in the area of executing
tests.

Let us not enable that by default, though, to protect
downstream users from themselves.  Some operating system
distribution builds optimistically run make -j N on all the
packages, and then have to deal with sporadic breakages when
some of those packages have parallel build bugs. We can
prevent TXR from ever being implicated in such a breakage by
turning off parallel building even if make -j requests it.

There will now be a ./configure --parallelmake option
to allow parallel builds, off by default.  The --maintainer
configuration mode will flip that default; configuring in
maintainer mode will enable parallel builds, unless explicitly
disabled with --no-parallelmake.

* Makefile (.NOTPARALLEL): Conditionally assert, if
parallelmake is false.
(tst/tests/014/dgram-stream.ok,
tst/tests/014/socket-basic.ok): Enforce order between these
two tests. They clash in their use of network ports so cannot
run at the same time.
(test.clean): test.clean must finish executing before tests;
enforce order.

* configure (parallelmake, parallelmake_given): New variables.
(help text): Add parallelmake option to help.
(gen_config_make): Generate the parallelmake make variable
into config.make.
New script section, defaulting parallelmake to y in maintainer
mode.

1 files changed, 8 insertions, 4 deletions

diff --git a/Makefile b/Makefile
index d0970049..2b234e53 100644
--- a/Makefile
+++ b/Makefile
@@ -24,10 +24,12 @@
 # OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-.NOTPARALLEL:
-
 -include config.make
 
+ifeq ($(parallelmake),)
+.NOTPARALLEL:
+endif
+
 VERBOSE :=
 TXR_CFLAGS := -iquote . $(if $(top_srcdir), -iquote $(top_srcdir)) \
               $(LANG_FLAGS) $(DIAG_FLAGS) \
@@ -409,6 +411,8 @@ tst/tests/016/%: TXR_DBG_OPTS :=
 tst/tests/017/%: TXR_DBG_OPTS :=
 tst/tests/018/%: TXR_DBG_OPTS :=
 
+tst/tests/014/dgram-stream.ok: | tst/tests/014/socket-basic.ok
+
 TST_EXPECTED  = $(word 2,$^)
 TST_OUT = $(patsubst %.expected,tst/%.out,$(TST_EXPECTED))
 
@@ -439,11 +443,11 @@ tst/%.ok: %.tl %.expected $(TXR)
 	$(call SH,touch $@)
 
 .PHONY: tests.clean
-tests.clean:
+tests.clean: | tests
 	rm -rf tst
 
 .PHONY: retest
-retest: tests.clean tests
+retest: | tests.clean tests
 
 define GREP_CHECK
 	$(V)if [ $$(grep -E $(1) $(SRCS) | wc -l) -ne $(3) ] ; then \