Date: Mon, 6 Nov 2017 00:07:52 -0800
From: Noah Misch <noah@leadboat.com>
To: pgsql-hackers@postgresql.org
Subject: Race to build pg_isolation_regress in "make -j check-world"
Message-ID: <20171106080752.GA1298146@rfd.leadboat.com>
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I've been enjoying the speed of parallel check-world, but I get spurious
failures from makefile race conditions.  Commit c66b438 fixed the simple ones.
More tricky is this problem of multiple "make" processes entering
src/test/regress concurrently, which causes failures like these:

  gcc: error: pg_regress.o: No such file or directory
  make[4]: *** [pg_isolation_regress] Error 1

  /bin/sh: ../../../src/test/isolation/pg_isolation_regress: Permission denied
  make -C test_extensions check
  make[2]: *** [check] Error 126
  make[2]: Leaving directory `/home/nm/src/pg/backbranch/10/src/test/isolation'

  /bin/sh: ../../../../src/test/isolation/pg_isolation_regress: Text file busy
  make[3]: *** [isolationcheck] Error 126
  make[3]: Leaving directory `/home/nm/src/pg/backbranch/10/src/test/modules/snapshot_too_old'

This is reproducible since commit 2038bf4 or earlier; "make -j check-world"
had worse problems before that era.  A workaround is to issue "make -j; make
-j -C src/test/isolation" before the check-world.  This problem doesn't affect
src/test/regress/pg_regress.  Every top-level "make" or "make install",
including temp-install, builds pg_regress.

I tried fixing this by building src/test/isolation at the same times we run
install-temp.  Naturally, that didn't help installcheck-world.  It also caused
multiple "make" processes to enter src/port concurrently.  I could fix both
check-world and installcheck-world with the attached hack of building
src/test/isolation during every top-level build or install.

The problem of multiple "make" processes in a directory (especially src/port)
shows up elsewhere.  In a cleaned tree, "make -j -C src/bin" or "make -j
installcheck-world" will do it.  For more-prominent use cases, src/Makefile
prevents this with ".NOTPARALLEL:" and building first the directories that are
frequent submake targets.  Perhaps we could fix the general problem with
directory locking; targets that call "$(MAKE) -C FOO" would first sleep until
FOO's lock is available.  That could be tricky to make robust.

For now, I propose back-patching the attached, sad hack.  Better ideas?

Thanks,
nm

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diff --git a/src/Makefile b/src/Makefile
index 380da92..febbced 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -28,6 +28,7 @@ SUBDIRS = \
 	pl \
 	makefiles \
 	test/regress \
+	test/isolation \
 	test/perl
 
 # There are too many interdependencies between the subdirectories, so
diff --git a/src/test/isolation/Makefile b/src/test/isolation/Makefile
index 8eb4969..efbdc40 100644
--- a/src/test/isolation/Makefile
+++ b/src/test/isolation/Makefile
@@ -15,6 +15,13 @@ OBJS =  specparse.o isolationtester.o $(WIN32RES)
 
 all: isolationtester$(X) pg_isolation_regress$(X)
 
+# Though we don't install these binaries, build them during installation
+# (including temp-install).  Otherwise, "make -j check-world" and "make -j
+# installcheck-world" would spawn multiple, concurrent builds in this
+# directory.  Later builds would overwrite files while earlier builds are
+# reading them, causing occasional failures.
+install: | all
+
 submake-regress:
 	$(MAKE) -C $(top_builddir)/src/test/regress pg_regress.o
 

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