m/pkg/event/memory: simplify and fix implementation

The old implementation is very complicated and has multiple concurrency 
bugs. One of these bugs is already described in a block comment. Another 
bug is that if a watcher is closed while being updated, `update` will 
try to send on the closed channel `deadletterSubmitC`, which panics.

This changes it to a much simpler implementation.

It could be further simplified it by dropping the Sync flag entirely, 
which is currently unused. Or we could use the buffered channel also for 
Sync values, and just skip dropping previous values. This still ensures 
that all values are delivered, but changes the semantics slightly: Set 
would no longer block until Get is called, if there is space in the 
channel buffer.

Additionally, there is no longer a memory leak when a watcher is 
repeatedly closed and readded, but Set never called. I added a test for 
this.

Fixes #127

Change-Id: I2775a36cf2d097c5961a09a387428774a068e1f5
Reviewed-on: https://review.monogon.dev/c/monogon/+/2875
Reviewed-by: Serge Bazanski <serge@monogon.tech>
Vouch-Run-CI: Serge Bazanski <serge@monogon.tech>
Tested-by: Jenkins CI
4 files changed
tree: df868c44f56171a2dfef74f844848a218820846d
  1. .github/
  2. build/
  3. cloud/
  4. go/
  5. intellij/
  6. metropolis/
  7. net/
  8. third_party/
  9. tools/
  10. version/
  11. .bazelignore
  12. .bazelproject
  13. .bazelrc
  14. .bazelrc.ci
  15. .bazelrc.sandboxroot
  16. .bazelversion
  17. .git-ignore-revs
  18. .gitignore
  19. BUILD.bazel
  20. CODING_STANDARDS.md
  21. go.mod
  22. go.sum
  23. LICENSE
  24. MODULE.bazel
  25. MODULE.bazel.lock
  26. README.md
  27. SETUP.md
  28. shell.nix
  29. WORKSPACE
README.md

Monogon Monorepo

This is the main repository containing the source code for the Monogon Platform.

This is pre-release software - take a look, and check back later!

Environment

Our build environment is self-contained and requires only minimal host dependencies:

  • A Linux machine or VM.
  • Bazelisk >= v1.15.0 (or a working Nix environment).
  • A reasonably recent kernel with user namespaces enabled.
  • Working KVM with access to /dev/kvm (if you want to run tests).

Our docs assume that Bazelisk is available as bazel on your PATH.

Refer to SETUP.md for detailed instructions.

Monogon OS

The source code lives in //metropolis (Metropolis is the codename of Monogon OS).

See the //metropolis/README.md for a developer quick start guide, or see the Monogon OS Handbook for user documentation.