Horton

Re: Refactoring backend fork+exec code

Heikki Linnakangas <hlinnaka@iki.fi>

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From: Heikki Linnakangas <hlinnaka@iki.fi>
To: Andres Freund <andres@anarazel.de>, Tristan Partin <tristan@neon.tech>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>, Thomas Munro <thomas.munro@gmail.com>
Date: 2023-11-29T23:36:25Z
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 11/10/2023 14:12, Heikki Linnakangas wrote:
> On 11/07/2023 01:50, Andres Freund wrote:
>>> Subject: [PATCH 3/9] Refactor CreateSharedMemoryAndSemaphores.
>>>
>>> Moves InitProcess calls a little later in EXEC_BACKEND case.
>>
>> What's the reason for this part?
> 
> The point is that with this commit, InitProcess() is called at same
> place in EXEC_BACKEND mode and !EXEC_BACKEND. It feels more consistent
> that way.
> 
>> ISTM that we'd really want to get away from plastering duplicated
>> InitProcess() etc everywhere.
> 
> Sure, we could do more to reduce the duplication. I think this is a step
> in the right direction, though.

Here's another rebased patch set. Compared to previous version, I did a 
little more refactoring around CreateSharedMemoryAndSemaphores and 
InitProcess:

- patch 1 splits CreateSharedMemoryAndSemaphores into two functions: 
CreateSharedMemoryAndSemaphores is now only called at postmaster 
startup, and a new function called AttachSharedMemoryStructs() is called 
in backends in EXEC_BACKEND mode. I extracted the common parts of those 
functions to a new static function. (Some of this refactoring used to be 
part of the 3rd patch in the series, but it seems useful on its own, so 
I split it out.)

- patch 3 moves the call to AttachSharedMemoryStructs() to 
InitProcess(), reducing the boilerplate code a little.


The patches are incrementally useful, so if you don't have time to 
review all of them, a review on a subset would be useful too.

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