Re: Threading in BGWorkers (!)

On Tue, 23 Jun 2020 at 17:26, Konstantin Knizhnik <k(dot)knizhnik(at)postgrespro(dot)ru>
wrote:

> On 23.06.2020 10:15, James Sewell wrote:
>
> Using multithreading in bgworker is possible if you do not use any
>> Postgres runtime inside thread procedures or do it in exclusive critical
>> section.
>> It is not so convenient but possible. The most difficult thing from my
>> point of view is error reporting.
>>
>
> Happy to be proved wrong, but I don't think this is correct.
>
> PostgreSQL can call sigprocmask() in your BGWorker whenever it wants, and
> "The use of sigprocmask() is unspecified in a multithreaded process" [1]
>
>
> Sorry, may be I missed something.
> But in my bgworker I am not using Postgres runtime at all (except initial
> bgworker startup code).
> So I am not using latches (which are based on signals), snapshots,...
> In my case bgworker has no connection to Postgres at all.
> Yes, it can still receives signals from Postmaster (SIGTERM, SIGHUP). But
> their handler are trivial and do not need to mask any signals.
>
> So may be in general case combination of signals and threads may cause
> some problems,
> but it doesn't mean that you can't create multithreaded bgworker.
>

Ah yes - sorry *I* missed something.

A multi threaded BGWorker which accesses shared memory and database via
SPI.

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