FreeBSD src
faf215c7ad
_without_ using fork(). The problem with YPPROC_ALL is that it transmits an entire map through a TCP pipe as the result of a single RPC call. First of all, this requires certain hackery in the XDR filter. Second, if the map being sent is large, the server can end up spending lots of time in the XDR filter sending to just the one client, while requests for other clients will go unanswered. My original solution for this was to fork() the request into a child process which terminates after the map has been transmitted (or the transfer is interrupted due to an error). This leaves the parent free to handle other requests. But this solution is kind of lame: fork() is relatively expensive, and we have to keep a cap on the number of child processes to keep from swamping the system. What we do now is grab control of the service transport handle and XDR handle from the RPC library and send the records one at a time ourselves instead of letting the RPC library do it. We send a record, then go back to the svc_run() loop and select() on the socket. If select() says we can still write data, we send the next record. Then we call svc_getreqset() and handle other RPCs and loop around again. This way, we can handle other RPCs between records. We manage multiple YPPROC_ALL requests using a circular queue. When a request is done, we dequeue it and destroy the handle. We also tag each request with a ttl which is decremented whevever we run the queue and a handle isn't serviced. This lets us nuke requests that have sat idle for too long (if we didn't do this, we might run out of socket descriptors.) Now all I have to do is come up with an async resolver, and ypserv won't need to fork() at all. :) Note: these changes should not go into 2.2 unless they get a very throrough shakedown before the final cutoff date. |
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