[SV 13862] Implement the .WAIT special target

The next version of the POSIX standard defines parallel execution
and requires the .WAIT special target as is implemented in some other
versions of make.

This implementation behaves similarly to others in that it does not
create a relationship between targets in the dependency graph, so
that the same two targets may be run in parallel if they appear as
prerequisites elsewhere without .WAIT between them.

Now that we support .WAIT it's trivial to also support prerequisites
of the .NOTPARALLEL special target, which forces the prerequisites of
those targets to be run serially (as if .WAIT was specified between
each one).

* NEWS: Announce the new .WAIT and .NOTPARALLEL support.
* doc/make.texi (Parallel Disable): A new section to discuss ways in
which parallel execution can be controlled.  Modify cross-refs to
refer to this section.
* src/dep.h (struct dep): Add a new wait_here boolean.
(parse_file_seq): Add PARSEFS_WAIT to check for .WAIT dependencies.
* src/file.c (split_prereqs): Use PARSEFS_WAIT.
(snap_deps): If .NOTPARALLEL has prerequisites, set .WAIT between
each of _their_ prerequisites.
(print_prereqs): Add back in .WAIT when printing prerequisites.
* src/implicit.c (struct patdeps): Preserve wait_here.
(pattern_search): Ditto.  Use PARSEFS_WAIT when parsing prereqs for
pattern rule expansion.
* src/read.c (check_specials): Don't give up early: remembering to
update these options is not worth the rare speedup.
(check_special_file): If .WAIT is given as a target show an error--
once--if it has prereqs or commands.
(record_files): Call check_special_file on each target.
(parse_file_seq): If PARSEFS_WAIT is given, look for .WAIT prereqs.
If we see one assume that we are building a struct dep chain and set
the wait_here option while not putting it into the list.
* src/remake.c (update_file_1): If wait_here is set and we are still
running, then stop trying to build this target's prerequisites.
* src/rule.c (get_rule_defn): Add .WAIT to the prerequisite list.
* src/shuffle.c (shuffle_deps): Don't shuffle the prerequisite list
if .WAIT appears anywhere in it.
* tests/scripts/targets/WAIT: Add a test suite for this feature.

1 files changed, 15 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index 5a8c85ec..4f37ec3f 100644
--- a/NEWS
+++ b/NEWS
@@ -46,6 +46,21 @@ https://sv.gnu.org/bugs/index.php?group=make&report_id=111&fix_release_id=109&se
   https://www.gnu.org/software/gnulib/manual/html_node/C99-features-assumed.html
   The configure script should verify the compiler has these features.
 
+* New feature: The .WAIT special target
+  If the .WAIT target appears between two prerequisites of a target, then
+  GNU make will wait for all of the targets to the left of .WAIT in the list
+  to complete before starting any of the targets to the right of .WAIT.
+  This feature is available in some other versions of make, and it will be
+  required by an upcoming version of the POSIX standard for make.
+  Different patches were made by Alexey Neyman <alex.neyman@auriga.ru> (2005)
+  and Steffen Nurpmeso <steffen@sdaoden.eu> (2020) that were useful but the
+  result is a different implementation (closer to Alexey's idea).
+
+* New feature: .NOTPARALLEL accepts prerequisites
+  If the .NOTPARALLEL special target has prerequisites then all prerequisites
+  of those targets will be run serially (as if .WAIT was specified between
+  each prerequisite).
+
 * New feature: The .NOTINTERMEDIATE special target
   .NOTINTERMEDIATE Disables intermediate behavior for specific files, for all
   files built using a pattern, or for the entire makefile.