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Re: [bug #49844] 'make -j' without explicit process count sometimes does
Sven C. Dack
Re: [bug #49844] 'make -j' without explicit process count sometimes doesn't parallelize
Thu, 22 Jun 2017 13:01:36 +0100
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0
this isn't a bug, but it's how the -j option works.
From the manual:
-j [jobs], --jobs[=jobs]
Specifies the number of jobs (commands) to run
there is more than one -j option, the last one is
the -j option is given without an argument, make will
the number of jobs that can run simultaneously.
Specifying -j1 or -j 1 are the same here.
Your problem is that you are using numbers as target names. So it's not
a bug, because you are literally telling make to run only a single job.
You either have to restrict the number of jobs by giving an explicit
count or by limiting it with a load average ( -l option) or use
non-numerical make targets such as "t1 t2 t3 ..." or simply add another
flag after -j to make.
From my own experience is it generally better to limit the number of
jobs to what is reasonable or otherwise risk setting off a fork bomb - a
run-away process which spawns too many process too fast and brings the
system to a halt.
If it really needs to be unlimited then using non-numerical targets is
what you can do:
$ seq 1000 | sed 's,^,t,' | xargs -n1000 make -j
which results in:
$ make -j t1 t2 t3 ...
Or if it needs to be unlimited and it has to be numerical arguments can
you simply do this:
$ seq 1000 | xargs -n1000 make -j -C .
which results in:
$ make -j -C . 1 2 3 ...
The -C option tells make to change the directory to the current
directory and avoids the target 1 to be treated as an optional argument
On 21/06/17 20:39, Michael Builov wrote:
Follow-up Comment #1, bug #49844 (project make):
There is a bug in your trivial example:
1) 'seq 1000 | xargs -n1000 make -j5'
'make -j5 1 2 3 4 5 6 7 ...'
2) 'seq 1000 | xargs -n1000 make -j'
'make -j 1 2 3 4 5 6 7 ...'
As we can see, in second example '1' after '-j' make interprets as number of
jobs, so "it not do any parallelization at all".
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