Opam for windows: make compiler does not honor -j argument

[Chimrod]

I’m compiling opam in a virtual windows machine. I’ve assigned a limited number of cores to that virtual machine, and the compilation freeze during the step make compiler. As consequence, I need to open the task manager and manually kill the process x86_64-w64-mingw32-gcc.

After some tries and restart, I’ve found that the script bootstrap-ocaml.sh override the -j argument given to the original make job. It looks likes make detect here the number of core for the hardware cpu, and create too many processes and fall into race condition which bloc the whole compilation task.

After editing the script and removing the -j argument given in the make commands I’ve been able to compile the task without any issue.

[kit-ty-kate]

I'm suddenly having the same issue after upgrading cygwin to the latest version (3.5.1), it was working just fine minutes before on the same machine but after the upgrade i deterministically can't compile OCaml anymore.. sigh

[kit-ty-kate]

I sent a bug-report to the Cygwin bug-tracker: https://cygwin.com/pipermail/cygwin/2024-February/255561.html

[dra27]

Me too - thanks for reporting! Just as a data point, I had been using Cygwin 3.5.0 on bare metal with no problems to build OCaml (this was in opam itself), but I hadn't run make cold. Are you both using VMs? My desktop has a crazy high core count, but I'm seeing the same problem in a Hyper-V VM even with 16 vCPUs (-j16 is about the best parallelism OCaml's build can achieve anyway).

[kit-ty-kate]

No i'm on baremetal (4core machine on Intel i5-750)

[kit-ty-kate]

Cygwin 3.5.3 was just released and should have fixed the underlying bug.

The lack of parametricity for make compiler is still a problem though but not urgently to be fixed before the 2.2.0 release so I've removed it from the 2.2.0 project. We can fix that later.

If you're still experiencing the underlying Cygwin bug with the new release though please don't hesitate to tell us and we'll look into it.

[Chimrod]

Thank you for keeping me informed and your involvement in a general way, this is very appreciated :)