executor: mount isolated POSIX shared memory per action - #34
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Python multiprocessing fails inside an action sandbox while creating a POSIX
named semaphore:
```text
executor = ProcessPoolExecutor(max_workers=5, mp_context=multiprocessing.get_context("spawn"))
...
self._semlock = _multiprocessing.SemLock(...)
FileNotFoundError: [Errno 2] No such file or directory
```
Create `/dev/shm` alongside each action's existing base directories and mount a
private 64 MiB tmpfs after entering its mount namespace. Keep the mount
`nosuid,nodev,noexec`, give it the standard sticky world-writable mode, and
perform the mount before dropping sandbox privileges. Extend the existing base
directory test to cover the new mount point.
The failure was reproduced remotely with
`//project/oai_sandbox:pytest -k test_get_minijail_concurrent_calls_only_one_download`
using Bazel `9.3.0-actiond-dzbarsky14`.
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Python multiprocessing fails inside an action sandbox while creating a POSIX
named semaphore:
Create
/dev/shmalongside each action's existing base directories and mount aprivate 64 MiB tmpfs after entering its mount namespace. Keep the mount
nosuid,nodev,noexec, give it the standard sticky world-writable mode, andperform the mount before dropping sandbox privileges. Extend the existing base
directory test to cover the new mount point.
The failure was reproduced remotely with
//project/oai_sandbox:pytest -k test_get_minijail_concurrent_calls_only_one_downloadusing Bazel
9.3.0-actiond-dzbarsky14.After rebuilding the guest and preserving the existing CAS-maintenance wrapper, the same test passes remotely with 300 submitted process-pool calls (one real remote test execution; invocation
a36afe32-8b71-4ccf-ab6c-47f357cb77d8).