bitbake: runqueue: Optimise multiconfig with overlapping setscene

Currently if a multiconfig build contains different configurations which
have overlapping sstate artefacts, it will build them multiple times.
This is clearly suboptimal and not what users want/expect.

This adds code to detect this and stall all but one of the setscne tasks
so that once its built, it can be found by the other tasks.

We take care to iterate the multiconfigs in order so try and avoid
dependency loops. We also match on PN+taskname+taskhash since this is
what we know sstate in OE-Core would use. There are some tasks even within
a multiconfig which match hashes (mostly do_populate_lic tasks) but those
have a much higher chance of circular dependency so aren't work attempting
to optimise.

If a deadlock does occur the build will be slower but there is code to
unbreak such a deadlock so it hopefully doens't break anything.

Comments are injected into the test tasks so they have different task
hashes and a new test for this optimisation is added.

(Bitbake rev: a75c5fd6d4ec56836de0be2fe679c81297a080ad)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/tests/runqueue-tests/classes/base.bbclass

@@ -4,7 +4,9 @@ SSTATEVALID ??= ""
 def stamptask(d):
     import time
 
-    thistask = d.expand("${PN}:${BB_CURRENTTASK}") 
+    thistask = d.expand("${PN}:${BB_CURRENTTASK}")
+    if d.getVar("BB_CURRENT_MC") != "default":
+        thistask = d.expand("${BB_CURRENT_MC}:${PN}:${BB_CURRENTTASK}")
     if thistask in d.getVar("SLOWTASKS").split():
         bb.note("Slowing task %s" % thistask)
         time.sleep(0.5)
@@ -13,48 +15,63 @@ def stamptask(d):
         f.write(thistask + "\n")
 
 python do_fetch() {
+    # fetch
     stamptask(d)
 }
 python do_unpack() {
+    # unpack
     stamptask(d)
 }
 python do_patch() {
+    # patch
     stamptask(d)
 }
 python do_populate_lic() {
+    # populate_lic
     stamptask(d)
 }
 python do_prepare_recipe_sysroot() {
+    # prepare_recipe_sysroot
     stamptask(d)
 }
 python do_configure() {
+    # configure
     stamptask(d)
 }
 python do_compile() {
+    # compile
     stamptask(d)
 }
 python do_install() {
+    # install
     stamptask(d)
 }
 python do_populate_sysroot() {
+    # populate_sysroot
     stamptask(d)
 }
 python do_package() {
+    # package
     stamptask(d)
 }
 python do_package_write_ipk() {
+    # package_write_ipk
     stamptask(d)
 }
 python do_package_write_rpm() {
+    # package_write_rpm
     stamptask(d)
 }
 python do_packagedata() {
+    # packagedata
     stamptask(d)
 }
 python do_package_qa() {
+    # package_qa
     stamptask(d)
 }
 python do_build() {
+    # build
     stamptask(d)
 }
 do_prepare_recipe_sysroot[deptask] = "do_populate_sysroot"