[Mongrel] Problems with mongrel dying

Jan Svitok jan.svitok at gmail.com
Fri Nov 3 18:34:11 EST 2006

On 11/3/06, Ezra Zygmuntowicz <ezmobius at gmail.com> wrote:
> On Nov 3, 2006, at 8:50 AM, Kirk Haines wrote:
> > On 11/2/06, Zed A. Shaw <zedshaw at zedshaw.com> wrote:
> >
> >> That's probably the best you can do until you can find out why
> >> it's leaking.  My past
> >> experience has been to never trust Ruby's GC or any external C
> >> extensions you may be
> >> using.  I've combed through Mongrel to insane levels to root out
> >> all possible leaks I can.
> >> Yet, the Sync vs. Mutex bug and recent Array patch from Eric M.
> >> shows that Ruby's GC has
> >> a long way to go.
> >
> > I'll 1/2 second Zed's comments here.  I've spent a lot of time poking
> > around in Ruby internals looking at memory usage.  It is very easy for
> > someone to write a C extension that mismanages memory and causes Ruby
> > to leak, so always look suspiciously at an extension if you have a
> > leak that you can't find another cause for, unless you know with great
> > confidence that the extension is solid.
> >
> > The Ruby GC itself is pretty simple and does what it is supposed to.
> > It will tend to have performance issues as the set of objects in RAM
> > increases, though there are strategies a person can sometimes use to
> > manage that, if needed.
> >
> > The Sync vs Mutex thing, though, can not be laid at the foot of the
> > Ruby GC.  The problem is with Array.c not releasing it's data in a way
> > that allows the Ruby GC to handle it.   Refer back to the beginning of
> > this email about how easy it is to screw up memory management in C
> > extensions....
> >
> > Now, that said, if you are using arrays and are using push and shift
> > operations to manage an array like a queue (or any libraries, like
> > Mutex, that you are using do this), that _will_ bite you in the ass
> > with memory usage, because of this Array bug.
> >
> > Mutex has much better performance than Sync, though, especially if
> > there are more than a very small number of threads, so in this
> > specific case I continue to use a Mutex, but have patched around the
> > problemlematic Array usage by creating my own copy of the Mutex class
> > that uses Array in a way that doesn't suffer from the bug.
> >
> >
> > Kirk Haines
> Hey Kirk-
>         Would you mind sharing your patched mutex.rb file? I woudl
> appreciate it.

IIRC, the patch consist of replacing shift with pop, and push with
unshift respectively thus reversing the queue direction. The idea is
to avoid Array#shift as it retains the reference to the removed item.

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