[tz] [PROPOSED] Parallelize the main part of 'make to2050new.tzs'

[Paul Eggert]

This improves real-time performance of 'make -j4 to2050new.tzs' by
a factor of about 3.5 (from 120 s to 34 s) on my old 4-core desktop,
which runs Fedora 27 x86-64 atop an AMD Phenom II X4 910e.
* Makefile (ZDS): New macro.
($(ZDS)): New rule.  All targets are phony.
($(TZS_NEW)): Use it in a submake that is parallelized by GNU make -j.
(check_links): Depend on tzdata.zi, fixing a dependency bug.
* NEWS: Mention this.
---
 Makefile | 29 ++++++++++++++++++++---------
 NEWS     |  4 ++++
 2 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/Makefile b/Makefile
index fc15c3e..835f34b 100644
--- a/Makefile
+++ b/Makefile
@@ -640,19 +640,29 @@ posix_packrat:
 
 zones:		$(REDO)
 
+# dummy.zd is not a real file; it is mentioned here only so that the
+# top-level 'make' does not have a syntax error.
+ZDS = dummy.zd
+# Rule used only by submakes invoked by the $(TZS_NEW) rule.
+# It is separate so that GNU 'make -j' can run instances in parallel.
+$(ZDS): zdump
+		./zdump -i -c $(TZS_YEAR) '$(wd)/'$$(expr $@ : '\(.*\).zd') >$@
+
 $(TZS_NEW):	tzdata.zi zdump zic
-		mkdir -p tzs.dir
+		rm -fr tzs.dir
+		mkdir tzs.dir
 		$(zic) -d tzs.dir tzdata.zi
 		$(AWK) '/^L/{print "Link\t" $$2 "\t" $$3}' \
 		   tzdata.zi | LC_ALL=C sort >$@.out
 		wd=`pwd` && \
-		zones=`$(AWK) -v wd="$$wd" \
-				'/^Z/{print wd "/tzs.dir/" $$2}' tzdata.zi \
-			 | LC_ALL=C sort` && \
-		./zdump -i -c $(TZS_YEAR) $$zones >>$@.out
-		sed 's,^TZ=".*tzs\.dir/,TZ=",' $@.out >$@.sed.out
-		rm -fr tzs.dir $@.out
-		mv $@.sed.out $@
+		set x `$(AWK) '/^Z/{print "tzs.dir/" $$2 ".zd"}' tzdata.zi \
+			| LC_ALL=C sort -t . -k 2,2` && \
+		shift && \
+		ZDS=$$* && \
+		$(MAKE) wd="$$wd" TZS_YEAR=$(TZS_YEAR) ZDS="$$ZDS" $$ZDS && \
+		sed 's,^TZ=".*tzs\.dir/,TZ=",' $$ZDS >>$@.out
+		rm -fr tzs.dir
+		mv $@.out $@
 
 # If $(TZS) does not already exist (e.g., old-format tarballs), create it.
 # If it exists but 'make check_tzs' fails, a maintainer should inspect the
@@ -730,7 +740,7 @@ check_sorted: backward backzone iso3166.tab zone.tab zone1970.tab
 		$(AWK) '/^[^#]/ $(CHECK_CC_LIST)' zone1970.tab | \
 		  LC_ALL=C sort -cu
 
-check_links:	checklinks.awk $(TDATA_TO_CHECK)
+check_links:	checklinks.awk $(TDATA_TO_CHECK) tzdata.zi
 		$(AWK) -f checklinks.awk $(TDATA_TO_CHECK)
 		$(AWK) -f checklinks.awk tzdata.zi
 
@@ -964,3 +974,4 @@ zic.o:		private.h tzfile.h version.h
 .PHONY: public right_only right_posix signatures signatures_version
 .PHONY: tarballs tarballs_version typecheck
 .PHONY: zonenames zones
+.PHONY: $(ZDS)
diff --git a/NEWS b/NEWS
index 3d18e89..1d2827e 100644
--- a/NEWS
+++ b/NEWS
@@ -79,6 +79,10 @@ Unreleased, experimental changes
       already can use vanguard.zi; in this respect, current tzcode is
       bleeding-edge.
 
+    The Makefile should now be safe for parallelized builds, and 'make
+    -j to2050new.tzs' is now much faster on a multiprocoessor host
+    with GNU Make.
+
     When built with -DSUPPRESS_TZDIR, the tzcode library no longer
     prepends TZDIR/ to file names that do not begin with '/'.  This is
     not recommended for general use, due to its security implications.
-- 
2.14.3