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Subject: Re: Sporadic GNU make jobserver unavailable
In-Reply-To: <1ae0d609-dd05-48aa-b2bf-c3ccf39b86da@SystematicSW.ab.ca>
Date: Fri, 5 Dec 2025 19:26:56 +0100
Cc: Brian Inglis <Brian DOT Inglis AT SystematicSW DOT ab DOT ca>
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From: Dimitry Andric via Cygwin <cygwin AT cygwin DOT com>
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On 5 Dec 2025, at 14:37, Brian Inglis via Cygwin <cygwin AT cygwin DOT com> wrote:
> 
> 
> On 2025-12-05 02:18, Dimitry Andric via Cygwin wrote:
>> We're using Cygwin make to build several projects in parallel mode, e.g.
>> with -j 4 or sometimes higher settings, depending on the core count of
>> the machine.
>> Sporadically, and then I'm talking about "once a week" or so, random
>> jobs will fail with a non-repeatable error, and in _every_ case these
>> failures are preceded by a warning from make:
>>   make[4]: warning: jobserver unavailable: using -j1.  Add '+' to parent make rule.
>> Obviously the "Add '+' to parent rule" is nonsensical, since simply
>> running exactly the same job again almost always works fine. But there
>> is something flaky about make's jobserver under Windows.
>> FWIW one machine I just observed this on has the make-4.4.1-2 package,
>> which should use the "pipe" jobserver, if I interpret
>> https://cygwin.com/pipermail/cygwin-announce/2023-March/010972.html
>> correctly.
>> Does anybody know a way to further debug this issue? It must be some
>> rare race condition...
> 
> https://stackoverflow.com/questions/60702726/warning-jobserver-unavailable-using-j1-add-to-parent-make-rule

Yeah, I've read all those FAQs. The problem isn't in our Makefiles,
since they run just fine on Linux. It's only on Windows under Cygwin
that they break. :)

I'm fairly certain it's a make bug, but whether it's Windows specific,
or just a Cygwin issue, is not yet clear.

-Dimitry


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