I'll do so at lunch break/from home tonight. Thanks, Michael On Thu, 9 Dec 2004 16:19:20 +0000, Jules Bean wrote:

On 9 Dec 2004, at 15:30, Michael Walter wrote:

...

I continued toying with my toy web server, and I'm "sometimes" getting "Invalid argument" errors in hGetLine for a handle I retrieved from Network.listenOn.

My first guess would be that hGetLine would return invalid argument if it was called on a handle which represents a file which is now closed. However, testing in GHCI suggests that returns "illegal operation (handle is closed)". Could be different for network sockets, I suppose.

...

"Sometimes", because it works fine in the browser, except when I reload very frequently -- maybe it's related to some concurrency issues (I'm using forkIO to spawn off the handler process from the main server loop). When I wanted to benchmark the server using "ab" (Apache Benchmark), it didn't even "survive" one request but Fail'ed using that error message - ": hGetLine: Invalid argument".

I tried adjusting the buffering mode.

Do you have any ideas?

Sounds like a double-close error or something like that. Hard to say without seeing the code. Can you make a minimal example?

Jules

Yep - this program "sometimes" fails for me with such an error message: Fail: : hGetLine: invalid argument (Invalid argument) If I omit the forkIO and do synchronous processing, I noticed that Apache Benchmark connects a second time but closes the connection immediately. When I added a `catch` \e -> mainLoop socket at the end of the main loop, it worked fine. But when I reintroduced the forkIO, it seemed to be "hanging" in the main process's accept (when the fork failed with above's error message). Any ideas? Confusingly yours, Michael On Thu, 9 Dec 2004 14:29:10 -0500, Michael Walter wrote:

Hello again,

this test program should do the relevant parts for the bug -- on Windows it works fine, though, I'll have to check at home whether it's reproducable using it.

- Michael

module Test where

import Control.Concurrent import Network import System.IO

mainLoop socket = do (handle, _, _) <- accept socket forkIO $ do line <- hGetLine handle putStrLn line hPutStrLn handle "HTTP/1.0 200 OK\r" hPutStrLn handle "Content-Type: text/html\r" hPutStrLn handle "\r" hPutStrLn handle "Test\r" hClose handle mainLoop socket

main = withSocketsDo $ listenOn (PortNumber 8000) >>= mainLoop

On Thu, 9 Dec 2004 11:44:16 -0500, Michael Walter wrote:

...

I'll do so at lunch break/from home tonight.

Thanks, Michael

On Thu, 9 Dec 2004 16:19:20 +0000, Jules Bean wrote:

...

On 9 Dec 2004, at 15:30, Michael Walter wrote:

...

I continued toying with my toy web server, and I'm "sometimes" getting "Invalid argument" errors in hGetLine for a handle I retrieved from Network.listenOn.

My first guess would be that hGetLine would return invalid argument if it was called on a handle which represents a file which is now closed. However, testing in GHCI suggests that returns "illegal operation (handle is closed)". Could be different for network sockets, I suppose.

...

"Sometimes", because it works fine in the browser, except when I reload very frequently -- maybe it's related to some concurrency issues (I'm using forkIO to spawn off the handler process from the main server loop). When I wanted to benchmark the server using "ab" (Apache Benchmark), it didn't even "survive" one request but Fail'ed using that error message - ": hGetLine: Invalid argument".

I tried adjusting the buffering mode.

Do you have any ideas?

Sounds like a double-close error or something like that. Hard to say without seeing the code. Can you make a minimal example?

Jules

What is happening is that the socket is closed after the accept but before the hGetLine, so the handle is invalid (there is no socket any more)... This is correct behaviour when the client closes the connection whilst you are writing to it... The answer is just to catch the exception. Keean. Michael Walter wrote:

Yep - this program "sometimes" fails for me with such an error message:

Fail: : hGetLine: invalid argument (Invalid argument)

If I omit the forkIO and do synchronous processing, I noticed that Apache Benchmark connects a second time but closes the connection immediately. When I added a `catch` \e -> mainLoop socket at the end of the main loop, it worked fine.

But when I reintroduced the forkIO, it seemed to be "hanging" in the main process's accept (when the fork failed with above's error message).

Any ideas?

Confusingly yours, Michael

On Thu, 9 Dec 2004 14:29:10 -0500, Michael Walter wrote:

...

Hello again,

this test program should do the relevant parts for the bug -- on Windows it works fine, though, I'll have to check at home whether it's reproducable using it.

- Michael

module Test where

import Control.Concurrent import Network import System.IO

mainLoop socket = do (handle, _, _) <- accept socket forkIO $ do line <- hGetLine handle putStrLn line hPutStrLn handle "HTTP/1.0 200 OK\r" hPutStrLn handle "Content-Type: text/html\r" hPutStrLn handle "\r" hPutStrLn handle "Test\r" hClose handle mainLoop socket

main = withSocketsDo $ listenOn (PortNumber 8000) >>= mainLoop

On Thu, 9 Dec 2004 11:44:16 -0500, Michael Walter wrote:

...

I'll do so at lunch break/from home tonight.

Thanks, Michael

On Thu, 9 Dec 2004 16:19:20 +0000, Jules Bean wrote:

...

On 9 Dec 2004, at 15:30, Michael Walter wrote:

...

I continued toying with my toy web server, and I'm "sometimes" getting "Invalid argument" errors in hGetLine for a handle I retrieved from Network.listenOn.

My first guess would be that hGetLine would return invalid argument if it was called on a handle which represents a file which is now closed. However, testing in GHCI suggests that returns "illegal operation (handle is closed)". Could be different for network sockets, I suppose.

...

"Sometimes", because it works fine in the browser, except when I reload very frequently -- maybe it's related to some concurrency issues (I'm using forkIO to spawn off the handler process from the main server loop). When I wanted to benchmark the server using "ab" (Apache Benchmark), it didn't even "survive" one request but Fail'ed using that error message - ": hGetLine: Invalid argument".

I tried adjusting the buffering mode.

Do you have any ideas?

Sounds like a double-close error or something like that. Hard to say without seeing the code. Can you make a minimal example?

Jules

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