Re: Synchronization primitives (Was: Re: An example of bugs for Hot Standby)

Heikki Linnakangas <heikki.linnakangas@enterprisedb.com> writes:
> Streaming Replication introduces a few places with a polling pattern
> like this (in pseudocode):

> while()
> {
>   /* Check if variable in shared has advanced beoynd X */
>   SpinLockAcquire()
>   localvar = sharedvar;
>   SpinLockRelease()
>   if (localvar > X)
>     break;

>   /* Not yet. Sleep
>   pg_usleep(100);
> }

I trust there's a CHECK_FOR_INTERRUPTS in there ...

> It would be nice to have a new synchronization primitive for that.

Maybe.  The lock, the variable, the comparison operation, and the sleep
time all seem rather specific to each application.  Not sure that it'd
really buy much to try to turn it into a generic subroutine.
        regards, tom lane