[Haskell-cafe] sendfile leaking descriptors on Linux?

[Thomas Hartman]

Indeed, the error occurs when two processes are running at the same
time. One process isn't serving anything, and the other is just
looping, reported that it can't stop because the port is taken, and
repeating ad infinitum.

The loop I have is

ulimit -v 150000
while true; do
  echo starting patchtag: `date`
./dist/build/patchtagserver/patchtagserver --port=80 --
  echo patchtag exited: `date`
  echo patchtag exited: `date` >> patch-tag.log
  rm -f _local/patchtagserver_state.lock

The ulimit is so that it will die after consuming a reasonable amount
of memory. (I seem to have a memory leak somewhere, but it takes many
hours to get up to 150M.)

Everything else looks pretty standard to me. It seems to work as
designed most of the time, but occasionally will result in two
processes. I'm baffled as to how this happens.

If anybody has any idea, I would love to hear them.

2010/2/26 Jeremy Shaw <jeremy at n-heptane.com>:
> Hello,
> It will be interesting to see if that makes any difference -- it shouldn't.
> In happstack-server we use 'listenOn'. According to the documentation
> listenOn already sets ReuseAddr:
> http://hackage.haskell.org/packages/archive/network/2.2.1.7/doc/html/Network.html#v%3AlistenOn
> A quick look at the source code confirms it is calling:
>    setSocketOption sock ReuseAddr 1
> It sounds to be like you are getting the socket in use error because you
> have 2 processes running. Seems like the first one hasn't really died, but
> the second one is started anyway. How is it that your loop starts a second
> server when the first one has not finished?
> - jeremy
> On Fri, Feb 26, 2010 at 1:43 PM, Thomas Hartman <tphyahoo at gmail.com> wrote:
>>
>> Thanks, I altered my top level request handler as follows
>>
>> mysmartserver conf h stateProxy = do
>>      socket <- bindPort conf
>>
>>       <I added (setSocketOption socket ReuseAddr 1) here>
>>       <Should this be added in a comment, or even in function code,
>> in Happstack.Server.SimpleHTTP? What are the tradeoffs, when would you
>> *not* want ot use ReuseAddr?)
>>
>>      webserverTid <- forkIO $ simpleHTTPWithSocket socket conf h
>>      putStrLn . ( "starting happs server" ++ ) =<< time
>>
>>      control <- startSystemState stateProxy -- start the HAppS state
>> system
>>      putStrLn . ( "happs state started" ++ ) =<< time
>>
>>      waitForTermination
>>      killThread webserverTid
>>      stateShutdown control
>>
>> I can't replicate the error reliably so I won't know if it actually
>> fixed the problem for a while, therefore just leaving this cookie
>> crumb trail in case others may find it helpful.
>>
>> 2010/2/26 Brandon S. Allbery KF8NH <allbery at ece.cmu.edu>:
>> > On Feb 26, 2010, at 04:28 , Thomas Hartman wrote:
>> >>
>> >> me: Like mightybyte, I run my app in a shell loop that will just
>> >> restart it after a crash. But every once in a while it won't restart
>> >> because of the busy socket and I need to do a manual restart, killing
>> >> multiple processes (usually 2).
>> >>
>> >> the error I get is:
>> >>
>> >> bind: resource busy (Address already in use)
>> >
>> > This is on application restart?  It's not out of file descriptors, it's
>> > just
>> > the system keeping the socket around (netstat will show it in TIME_WAIT,
>> > or
>> > possibly in a shutdown negotiation state such as LAST_ACK, FIN_WAIT,
>> > etc.
>> >  TCP lacks *reliable* socket shutdown negotiation).
>> >
>> > You want to configure the socket with SO_REUSEADDR before trying to bind
>> > it
>> > (setSocketOption socket ReuseAddr 1).
>> >
>> > As to the portable version of sendfile, it's because not all systems
>> > offer a
>> > sendfile() system call.  Linux and *BSD do, and can use the native
>> > implementation; the portable version emulates sendfile() when it doesn't
>> > exist, at the price of additional CPU usage/system load (sendfile()
>> > having
>> > been created specifically to reduce system load in the common case for
>> > web
>> > servers).
>> >
>> > --
>> > brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery at kf8nh.com
>> > system administrator [openafs,heimdal,too many hats] allbery at ece.cmu.edu
>> > electrical and computer engineering, carnegie mellon university    KF8NH
>> >
>> >
>> >
>
>