RFR: JDK-8189376 Unsorted $(wildcard) causes instable module-deps.gmk

[Martin Buchholz]

So we're already successfully using this patch, it solves our real world
problem, it's a simple effective solution, but it points out architectural
problems that I would want to address if I was maintaining the build
system.  I might waste too much time re-reading "Recursive Make Considered
Harmful"

On Wed, Oct 25, 2017 at 1:09 AM, Magnus Ihse Bursie <
magnus.ihse.bursie at oracle.com> wrote:

> We have implicitly assumed that subsequent calls to $(wildcard) will
> return the same (sorted) order of files during a single build operation.
> This is not guaranteed since GNU make 3.82, but will be the case in
> practice on most systems due the the filesystem being used.
>
> It turned out that if the order was different, FindAllModuleInfos returned
> different strings which in turn caused module-deps.gmk to be re-generated
> at any time during the build, causing race conditions.
>
> The bug analysis and patch is contributed by Martin Buchholz.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8189376
> Patch inline:
> diff --git a/make/common/Modules.gmk b/make/common/Modules.gmk
> --- a/make/common/Modules.gmk
> +++ b/make/common/Modules.gmk
> @@ -249,10 +249,10 @@
>  # configuration.
>  # Param 1 - Module to find for, set to * for finding all
>  FindAllModuleInfos = \
> -    $(wildcard \
> +    $(sort $(wildcard \
>          $(foreach sub, $(SRC_SUBDIRS), \
>            $(patsubst %,%/$(strip $1)/$(sub)/module-info.java,
> $(TOP_SRC_DIRS))) \
> -        $(patsubst %,%/$(strip $1)/module-info.java,
> $(IMPORT_MODULES_SRC)))
> +        $(patsubst %,%/$(strip $1)/module-info.java,
> $(IMPORT_MODULES_SRC))))
>
>  # Find module-info.java files in the specific source dir
>  # Param 1 - Src dir to find module-info.java files in
>
> /Magnus
>