We have a server that accepts messages over a socket, spawning threads to process them. Processing these messages may cause other, outgoing connections, to be spawned. Under sufficient load, the main server loop (i.e. the call to accept, followed by a forkIO), becomes nonresponsive.

A smaller distilled testcase reveals that when sufficient socket activity is occurring, an incoming connection may not be responded to until other connections have been cleared out of the way, despite the fact that these other connections are being handled by separate threads. One issue that we’ve been trying to figure out is where this behavior arises from-- the GHC rts, the Network library, the underlying C libraries.

Have other GHC users doing applications with large amounts of socket usage observed similar behavior and managed to trace back where it originates from? Are there any particular architectural solutions that people have found to work well for these situations?

thanks,
  Jeff

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