[Haskell-cafe] Joels Time Leak
joelr1 at gmail.com
Thu Dec 29 08:20:41 EST 2005
There's no mistery here.
Threads take a while to unpickle the large server info packet when
the gang up on it all together. By adding the MVar you are basically
installing a door in front of the packet and only letting one thread
The end result is that you are pushing the timeout somewhere else as
threads spend a lot of time queued up and waiting to get through the
It takes a fraction of a second for a thread to unpickle the server
info packet. It needs to make a FFI call to ZLib's uncompress and
that's a blocking call since it's marked unsafe. I think that happens
rather quickly otherwise alerts would be showing here. What takes
time is unpickling the packet after it's uncompressed.
Why does it take a fraction of a second for 1 thread to unpickle and
several seconds per thread for several threads to do it at the same
time? I think this is where the mistery lies.
On Dec 29, 2005, at 1:02 PM, Adrian Hey wrote:
> I can reproduce the problem (ghc/Linux), but can't explain it. It
> seems very strange that friggin about with an otherwise irrelevant
> (AFAICT) MVar fixes the problem.
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