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Diffstat (limited to 'rules.mak')
| -rw-r--r-- | rules.mak | 36 |
1 files changed, 36 insertions, 0 deletions
@@ -399,3 +399,39 @@ GEN_SUBST = $(call quiet-command, \ %.json: %.json.in $(call GEN_SUBST) + +# Support for building multiple output files by atomically executing +# a single rule which depends on several input files (so the rule +# will be executed exactly once, not once per output file, and +# not multiple times in parallel.) For more explanation see: +# https://www.cmcrossroads.com/article/atomic-rules-gnu-make + +# Given a space-separated list of filenames, create the name of +# a 'sentinel' file to use to indicate that they have been built. +# We use fixed text on the end to avoid accidentally triggering +# automatic pattern rules, and . on the start to make the file +# not show up in ls output. +sentinel = .$(subst $(SPACE),_,$(subst /,_,$1)).sentinel. + +# Define an atomic rule that builds multiple outputs from multiple inputs. +# To use: +# $(call atomic,out1 out2 ...,in1 in2 ...) +# <TAB>rule to do the operation +# +# Make 4.3 will have native support for this, and you would be able +# to instead write: +# out1 out2 ... &: in1 in2 ... +# <TAB>rule to do the operation +# +# The way this works is that it creates a make rule +# "out1 out2 ... : sentinel-file ; @:" which says that the sentinel +# depends on the dependencies, and the rule to do that is "do nothing". +# Then we have a rule +# "sentinel-file : in1 in2 ..." +# whose commands start with "touch sentinel-file" and then continue +# with the rule text provided by the user of this 'atomic' function. +# The foreach... is there to delete the sentinel file if any of the +# output files don't exist, so that we correctly rebuild in that situation. +atomic = $(eval $1: $(call sentinel,$1) ; @:) \ + $(call sentinel,$1) : $2 ; @touch $$@ \ + $(foreach t,$1,$(if $(wildcard $t),,$(shell rm -f $(call sentinel,$1)))) |