Excerpts from Bardur Arantsson's message of Tue Feb 16 23:48:14 +0200 2010:
This cannot be fixed in the sendfile library, it is a feature of TCP that connections may linger for a long time unless explicit timeouts are used.
The problem is that the sendfile library *doesn't* wake up when the connection is terminated (because of threadWaitWrite) -- it doesn't matter what the timeout is.
Even server code without sendfile has the same issue since all writing to sockets ends up using threadWaitWrite. System.Timeout.timeout terminates a threadWaitWrite using asynchronous exceptions. If you want to detect dead sockets somewhat reliably without a timeout then there is SO_KEEPALIVE combined with polling SO_ERROR every few minutes. - Taru Karttunen