Re: Interrupts vs signals

Heikki Linnakangas <hlinnaka@iki.fi>

From: Heikki Linnakangas <hlinnaka@iki.fi>

To: Andres Freund <andres@anarazel.de>

Cc: Thomas Munro <thomas.munro@gmail.com>, Michael Paquier <michael@paquier.xyz>, Robert Haas <robertmhaas@gmail.com>, Fujii Masao <masao.fujii@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>

Date: 2026-02-20T14:22:48Z

Lists: pgsql-hackers

Attachments

v11-0001-Centralize-resetting-SIGCHLD-handler.patch (text/x-patch) patch v11-0001
v11-0002-Refactor-how-some-aux-processes-advertise-their-.patch (text/x-patch) patch v11-0002
v11-0003-Replace-Latches-with-Interrupts.patch (text/x-patch) patch v11-0003
v11-0004-Introduce-PendingInterrupts-with-separate-flags-.patch (text/x-patch) patch v11-0004

On 18/02/2026 02:11, Heikki Linnakangas wrote:
> On 14/02/2026 23:56, Andres Freund wrote:
>> Could we have the mask of interrupts that WaitInterrupt() is waiting 
>> for in a
>> second variable? That way we could avoid interrupting WaitInterrupt() 
>> when
>> raising or sending a signal that WaitInterrupt() is not waiting for.  
>> I think
>> that can be one race-freely with a bit of care?
> 
> Yeah, I thought of that, but I'm not sure what the right tradeoff here 
> is. I doubt the spurious wakeups matter much in practice. Then again, 
> maybe it's not much more complicated, so maybe I should try that.
> 
> Now with this new version, the same consideration applies to the 
> CFI_ATTENTION flag I added. We could expose a process's 
> CheckForInterruptsMask alongside the pending interrupts, so it would be 
> SendInterrupt()'s responsibility to check if the receiving backend's 
> CheckForInterruptsMask includes the interrupt that's being sent. That 
> would similarly eliminate the "false positive" ProcessInterrupts() calls 
> from CHECK_FOR_INTERRUPTS(), by moving the logic to the senders. The 
> SLEEPING_ON_INTERRUPTS and CFI_ATTENTION flags are quite symmetrical.

I tried that approach, exposing an "attention bitmask" where a backend 
advertises which interrupts it's currently interested in. I think I like it.

Patch attached. The relevant changes for this "attention mechanism" are 
in the last patch, but there are some other small changes too so this 
split into patches is a little messy. I moved the list of standard 
interrupts to a separate header file, for example. So for reviewing, I 
recommend reading the resulting interrupt.h and interrupt.c files after 
applying all the patches, instead of trying to read the diff for those.

- Heikki

Commits

Ignore SIGINT in walwriter and walsummarizer
- a92b809f9da1 19 (unreleased) landed
Split WaitEventSet functions to separate source file
- 393e0d231405 18.0 landed
Use ModifyWaitEvent to update exit_on_postmaster_death
- 84e5b2f07a5e 18.0 landed
Remove unused ShutdownLatchSupport() function
- a98e4dee63ce 18.0 landed
Rename two functions that wake up other processes
- 368d8270c838 18.0 landed
Use ProcNumbers instead of direct Latch pointers to address other procs
- a9c546a5a378 18.0 landed
Clean up WaitLatch calls that passed latch without WL_LATCH_SET
- f9ecb57a506a 18.0 landed
Remove unneeded #include
- 094ae071605d 18.0 landed
Remove unused latch
- 6c0c49f7d37d 18.0 landed
Remove support for background workers without BGWORKER_SHMEM_ACCESS.
- 80a8f95b3bca 15.0 cited