Horton

Re: Refactoring backend fork+exec code

Heikki Linnakangas <hlinnaka@iki.fi>

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From: Heikki Linnakangas <hlinnaka@iki.fi>
To: Tristan Partin <tristan@neon.tech>, Andres Freund <andres@anarazel.de>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>, Thomas Munro <thomas.munro@gmail.com>
Date: 2023-12-01T12:10:03Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Avoid 0-length memcpy to NULL with EXEC_BACKEND

  2. Tighten check for --forkchild argument when spawning child process

  3. Add missing PGDLLIMPORT markings

  4. Remove assertions that some compiler say are tautological

  5. Move code for backend startup to separate file

  6. Refactor postmaster child process launching

  7. Move some functions from postmaster.c to a new source file

  8. Split registration of Win32 deadchild callback to separate function

  9. Improve log messages referring to background worker processes

  10. Move initialization of the Port struct to the child process

  11. Pass CAC as an argument to the backend process

  12. Set socket options in child process after forking

  13. Fix references to renamed function in comments

  14. Use MyBackendType in more places to check what process this is

  15. Remove MyAuxProcType, use MyBackendType instead

  16. Replace BackendIds with 0-based ProcNumbers

  17. Redefine backend ID to be an index into the proc array

  18. Remove superfluous 'pgprocno' field from PGPROC

  19. Fix incorrect comment on how BackendStatusArray is indexed

  20. Refactor how InitProcess is called

  21. Pass BackgroundWorker entry in the parameter file in EXEC_BACKEND mode

  22. Refactor CreateSharedMemoryAndSemaphores

  23. Silence Valgrind complaint with EXEC_BACKEND

  24. Adjust obsolete comment explaining set_stack_base().

  25. Print lwlock stats also for aux processes, when built with LWLOCK_STATS

  26. Move canAcceptConnections check from ProcessStartupPacket to caller.

  27. Fix crash on syslogger startup

  28. Refactor ListenSocket array.

  29. Use FD_CLOEXEC on ListenSockets

  30. Don't leak descriptors into subprograms.

  31. Use WaitEventSet API for postmaster's event loop.

  32. Rearrange postmaster's startup sequence for better syslogger results.

  33. Fix and enhance the assertion of no palloc's in a critical section.

Attachments

On 30/11/2023 20:44, Tristan Partin wrote:
> Patches 1-3 seem committable as-is.

Thanks for the review! I'm focusing on patches 1-3 now, and will come 
back to the rest after committing 1-3.

There was one test failure with EXEC_BACKEND from patch 2, in 
'test_shm_mq'. In restore_backend_variables() I checked if 'bgw_name' is 
empty to decide if the BackgroundWorker struct is filled in or not, but 
it turns out that 'test_shm_mq' doesn't fill in bgw_name. It probably 
should, I think that's an oversight in 'test_shm_mq', but that's a 
separate issue.

I did some more refactoring of patch 2, to fix that and to improve it in 
general. The BackgroundWorker struct is now passed through the 
fork-related functions similarly to the Port struct. That seems more 
consistent.

Attached is new version of these patches. For easier review, I made the 
new refactorings compared in a new commit 0003. I will squash that 
before pushing, but this makes it easier to see what changed.

Barring any new feedback or issues, I will commit these.

-- 
Heikki Linnakangas
Neon (https://neon.tech)