URL:
<https://savannah.gnu.org/bugs/?54854>
Summary: multi-target rules invoked too often with -j2
Project: make
Submitted by: bmwiedemann
Submitted on: Wed 17 Oct 2018 11:08:15 AM UTC
Severity: 3 - Normal
Item Group: None
Status: None
Privacy: Public
Assigned to: None
Open/Closed: Open
Discussion Lock: Any
Component Version: None
Operating System: None
Fixed Release: None
Triage Status: None
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Details:
Seen in the wild at https://github.com/github/hub/pull/1892
I made a minimal reproducer (attached).
To reproduce:
tar xf makebug.tar.gz
cd makebug/
make clean ; time make -j2
make clean ; time make -j1
notice how the -j2 takes longer than -j1
because in make -j1, the multi-target rule to create all man-pages is just
invoked once, but with -j2 it is invoked three times - once per input file,
not only wasting compute resources, but also creating a chance for race
conditions.
Maybe there is a better (parallelism-safe) way to specify such cases where one
command turns many input files into many output files than the bison-example
at https://www.gnu.org/software/make/manual/make.html#Pattern-Examples ?
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File Attachments:
-------------------------------------------------------
Date: Wed 17 Oct 2018 11:08:15 AM UTC Name: makebug.tar.gz Size: 16KiB By:
bmwiedemann
<http://savannah.gnu.org/bugs/download.php?file_id=45219>
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