Getting Started with QNX Neutrino - QNX Software Systems

© 2009, QNX Software Systems GmbH & Co. KG. Using timers
}
}
return;
fprintf (stderr, "Table full, message from rcvid %d ignored, "
"client blocked\n", rcvid);
break;
// client with data
case MT_SEND_DATA:
// see if we can find another client to reply to with
// this client’s data
for (i = 0; i < MAX_CLIENT; i++) {
if (clients [i].in_use) {
// found one -- reuse the incoming message
// as an outgoing message
msg -> messageType = MT_OK;
// reply to BOTH CLIENTS!
MsgReply (clients [i].rcvid, EOK, msg,
sizeof (*msg));
MsgReply (rcvid, EOK, msg, sizeof (*msg));
}
}
clients [i].in_use = 0;
return;
}
}
fprintf (stderr, "Table empty, message from rcvid %d ignored, "
"client blocked\n", rcvid);
break;
Notes
Some general notes about the code:
• If there’s no one waiting and a data message arrives, or there’s no room in the list
for a new waiter client, we print a message to standard error, but never reply to the
client. This means that some clients could be sitting there, REPLY-blocked forever
— we’ve lost their receive ID, so we have no way to reply to them later.
This is intentional in the design. You could modify this to add MT_NO_WAITERS
and MT_NO_SPACE messages, respectively, which can be returned whenever these
errors were detected.
• When a waiter client is waiting, and a data-supplying client sends to it, we reply to
both clients. This is crucial, because we want both clients to unblock.
• We reused the data-supplying client’s buffer for both replies. This again is a style
issue — in a larger application you’d probably have to have multiple types of return
values, in which case you may not want to reuse the same buffer.
April 30, 2009 Chapter 3 • Clocks, Timers, and Getting a Kick Every So Often 155