[build] Fix parallel make hang by disabling dotnet build servers (#24903)

Parallel make (e.g. 'make all -j8', 'make world') has been hanging
for a while at the end of the build. This is a long-standing issue
(#13355) that has been patched
three times
(#15407,
#21315,
#22300) without fully fixing the
root cause.

The problem: when using parallel make, GNU Make uses a jobserver with
pipe-based file descriptors to coordinate sub-makes. The dotnet CLI
can start background build servers (MSBuild server, Roslyn/VBCSCompiler)
that inherit these file descriptors but never close them. Make then
waits for those file descriptors to close (which won't happen until
the servers exit - which they typically do about 10 minutes without
activity), thinking there are still active jobs.

The previous workaround attempted to shut down and force-kill dotnet
processes after the build via a 'shutdown-build-server' target. This
approach was unreliable because:
- The shutdown ran from a double-colon all-hook:: rule with no
  prerequisites, so with -j it could execute in parallel with (or
  before) the actual build, killing nothing.
- Build servers started by later subdirectories (e.g. tests/) after
  the dotnet/ shutdown were never killed.
- The process-matching regex pattern might not match all server
processes.

Ideally this would be fixed in when launching the build servers, by
making them not inherit handles. Unfortunately this is currently not
possible: dotnet/runtime#13943 (although this
might change in a not so
distant future: dotnet/runtime#123959)

The workaround: disable build servers entirely via environment variables
in
Make.config:
- DOTNET_CLI_USE_MSBUILD_SERVER=0: prevents the MSBuild server
  https://learn.microsoft.com/en-us/visualstudio/msbuild/msbuild-server

https://github.com/dotnet/msbuild/blob/main/documentation/MSBuild-Server.md
- UseSharedCompilation=false: prevents the Roslyn compiler server
(VBCSCompiler)
  dotnet/roslyn#27975
- MSBUILDDISABLENODEREUSE=1: prevents MSBuild node reuse
  https://github.com/dotnet/msbuild/wiki/MSBuild-Tips-&-Tricks

This eliminates the root cause - no background servers means no
inherited file descriptors means no hang. The shutdown-build-server
target and its invocations are removed as they are no longer needed.

Additionally, 'make world' now prints the installed workloads at the
end of the build for visibility.

Build without changes:
> make world  2149.57s user 258.32s system 107% cpu 37:30.19 total

Build with changes:
> make world  2242.74s user 286.38s system 354% cpu 11:52.55 total

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: dalexsoto

Make.config

@@ -403,6 +403,15 @@ DOTNET_DIR=$(abspath $(TOP)/builds/downloads/$(DOTNET_INSTALL_NAME))
 export DOTNET_ROOT=$(DOTNET_DIR)
 # dotnet now is being looked up in the PATH
 export PATH := $(DOTNET_DIR):$(PATH)
+
+# Disable build servers to prevent parallel make from hanging.
+# Build servers (MSBuild server, Roslyn/VBCSCompiler) inherit jobserver file
+# descriptors from make, and don't close them when daemonizing. This prevents
+# make from detecting that all jobs have finished, causing it to hang
+# indefinitely at the end of the build.
+export DOTNET_CLI_USE_MSBUILD_SERVER=0
+export UseSharedCompilation=false
+export MSBUILDDISABLENODEREUSE=1
 DOTNET=$(DOTNET_DIR)/dotnet
 DOTNET_BCL_DIR:=$(abspath $(TOP)/packages/microsoft.netcore.app.ref/$(DOTNET_BCL_VERSION)/ref/$(DOTNET_TFM))
 # when bumping to a new .NET version, there may be a period when some parts of .NET is still on the old .NET version, so handle that here for DOTNET_BCL_DIR

Makefile

@@ -32,6 +32,8 @@ world: check-system
 	@$(MAKE) reset-versions
 	@$(MAKE) all -j8
 	@$(MAKE) install -j8
+	@echo "Build is done, the following workloads were built:"
+	@$(DOTNET) workload list
 
 .PHONY: check-system
 check-system:
@@ -68,9 +70,6 @@ install-hook::
 		exit 1; \
 	fi
 
-all-hook install-hook::
-	$(Q) $(MAKE) -C dotnet shutdown-build-server
-
 dotnet-install-system:
 	$(Q) $(MAKE) -C dotnet install-system
 

dotnet/Makefile

@@ -536,23 +536,3 @@ clean-local::
 	$(Q) $(DOTNET) restore package/workaround-for-maccore-issue-2427/restore.csproj /bl:package/workaround-for-maccore-issue-2427/restore.binlog $(MSBUILD_VERBOSITY)
 	$(Q) touch $@
 
-# We need to shut down the builder server, because:
-#   We're using parallel make, and parallel make will start a jobserver, managed by file descriptors, where these file descriptors must be closed in all subprocesses for make to realize it's done.
-#   'dotnet pack' might have started a build server
-#   The build server does not close any file descriptors it may have inherited when daemonizing itself.
-#   Thus the build server (which will still be alive after we're done building here) might have a file descriptor open which make is waiting for.
-#   The proper fix is to fix the build server to close its file descriptors.
-#   The intermediate working is to shut down the build server instead. An alternative solution would be to pass /p:UseSharedCompilation=false to 'dotnet pack' to disable the usage of the build server.
-#
-# The 'shutdown-build-server' is executed in a sub-make (and not as a dependency to the all-hook target),
-# to make sure it's executed after everything else is built in this file.
-all-hook::
-	$(Q) $(MAKE) shutdown-build-server
-
-shutdown-build-server:
-	$(Q) echo "Shutting down build servers:"
-	$(Q) $(DOTNET) build-server shutdown | sed 's/^/    /' || true
-	$(Q) echo "Listing .NET processes still alive:"
-	$(Q) pgrep -lf "^$(DOTNET)" | sed 's/^/    /' || true
-	$(Q) echo "Killing the above mentioned processes."
-	$(Q) pkill -9 -f "^$(DOTNET)" | sed 's/^/    /' || true