Re: Latch implementation that wakes on postmaster death on both win32 and Unix

On 5 July 2011 07:49, Heikki Linnakangas
<heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
> Good point, and testing shows that that is exactly what happens at least on
> Linux (see attached test program). So, as the code stands, the children will
> go into a busy loop until the grandparent calls waitpid(). That's not good.
>
> In that light, I agree we should replace kill() in PostmasterIsAlive() with
> read() on the pipe. It would react faster than the kill()-based test, which
> seems like a good thing. Or perhaps do both, and return false if either test
> says the postmaster is dead.

Hmm. Why assume that the opposite problem doesn't exist? What if the
kill-based test is faster than the read() on the pipe on some platform
or under some confluence of events?

I suggest that we agree on a standard for determining whether or not
the postmaster is dead and stick to it - that's already the case on
Windows. Since that standard cannot be the kill() based test, because
that would make a postmaster death aware latch implementation
impossible, it has to be the read() test proposed by Florian.

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Peter Geoghegan       http://www.2ndQuadrant.com/
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