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Message ID: 553
Entry time: 14 Jan 2009
In reply to: 546
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| Author: |
Stefan Ritt |
| Topic: |
Info |
| Subject: |
odb "hot link" magic explored |
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| KO wrote: | | note 1: I do not completely understand the ss_suspend_xxx() stuff. The best I can tell is it creates a number of udp sockets bound to the local host and at least one udp rpc receive socket ultimately connected to the cm_dispatch_rpc() function. |
The ss_suspend_xxx() stuff is indeed the most complicated thing in midas an I have to remind myself always
on how this works. So let me try again:
The basic idea is that for a high performance system, you cannot do the inter-process communication via
polling. That would waste CPU time. Inter-process communication is necessary for for buffer manager
(producer notifies consumer when new events are there), for the RPC mechanism (odbedit tells mlogger to
start a run) or for ODB hot-links. To avoid polling, the inter-process communication works with sockets (UDP
and TCP). This allows to use the select() call, which suspends the calling process until some socket
receives data or a pre-defined time-out expires. This is the only portable method I found which works under
unix and windows (signals are only poorly supported under windows).
So after creating all sockets, ss_suspend() does a select() on these sockets:
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_suspend_struct[idx].listen_socket | Server side for any new RPC connection (each client is also a RPC server which gets contacted directly during run transitions for example
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_suspend_struct[idx].server_acception.recv_sock | Receive socket (TCP) for any active RPC connection
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_suspend_struct[idx].server_acception.event_sock | Receive socket (TCP) for bare events (bypassing RPC layer for performance reasons)
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_suspend_struct[idx].server_connection->recv_sock | Outgoing TCP connection to mserver. Used for example for hot-link notifications from mserver
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_suspend_struct[idx].ipc_recv_socket | UDP socket for inter-process notification
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For each socket there is a dispatch function, which gets called if that socket receives some data. Hope this sheds some light on the guts of that. |