EMULATE=1 not concurrency safe

[kaspar030]

Description

The emulation machinery is using fixed port numbers / socket files for serial and monitor sockets, which makes them unusable in the parallel case (e.g., CI).
Could it use per-application socket files?

#17434 is blocked on this.

Steps to reproduce the issue

Run two instances of EMULATE=1 make test for e.g., microbit.

Expected results

Test passes.

Actual results

/tmp/dwq.0.5048392832189235/a33c1c69a48300216f746cb52394974e/dist/tools/emulator/term.sh qemu microbit /tmp/dwq.0.5048392832189235/a33c1c69a48300216f746cb52394974e/tests/xtimer_usleep /tmp/dwq.0.5048392832189235/a33c1c69a48300216f746cb52394974e/dist/tools/pyterm/pyterm '-p "/tmp/riot_tests_xtimer_usleep_microbit_uart" -b "115200" ' /tmp/riot_tests_xtimer_usleep_microbit_uart 
qemu-system-arm -machine microbit -device loader,file=/tmp/dwq.0.5048392832189235/a33c1c69a48300216f746cb52394974e/build/tests_xtimer_usleep.elf -serial telnet::5555,server,nowait,nodelay -monitor telnet::45454,server,nowait -nographic
qemu-system-arm: -monitor telnet::45454,server,nowait: Failed to find an available port: Address already in use
make[2]: *** [/tmp/dwq.0.5048392832189235/a33c1c69a48300216f746cb52394974e/Makefile.include:853: emulate] Error 1

Versions

[kfessel]

Instead of socat tcp <-> pty
we could socat pty <-> pty

socat pty,link=/tmp/soin,raw,echo=0 pty,link=/tmp/soout,raw,echo=0

and the connect qemu to it

qemu -serial /tmp/soin

e.g. in term.sh soin pty with the same name as PORT ($6) +_in

-- qemu can also generate pty but it auto allocates the pty name (pyt has no parameters)

[kaspar030]

and the connect qemu to it

well, that would work, but, the current machinery is just setting socat as terminal, and starts qemu first. Not sure if that order is (easily) fixable.

[kaspar030]

apparrently qemu's pty takes an id=<n> parameter, allowing to control the name of the pty somewhat. maybe that can be used.

[kfessel]

sadly pty provides not control which path it goe to
id is the backend id to identify which device goes where in qemu it is not the path

-chardev pty,id=id
    Create a new pseudo-terminal on the host and connect to it. pty does not take any options.
    pty is not available on Windows hosts.

pty
    [Linux only] Pseudo TTY (a new PTY is automatically allocated)

compar to

 -chardev serial,id=id,path=path

https://www.qemu.org/docs/master/system/invocation.html#hxtool-6

[kfessel]

may be Closed

please check if you can employ the changes by #17679

[kaspar030]

Yeah, #17434 has been waiting in the queue since #17679 got merged... let's see

[kaspar030]

fixed by #17679