Inside Macintosh: Networking With Open Transport / Part 1 - Open Transport Essentials

Chapter 5 - Programming With Open Transport

Improving Performance

The following suggestions for improving performance were drawn up with servers in mind; however, if your application needs to handle multiple connection requests, you might find the section "Streamlining Endpoint Creation" useful. For additional information on handling throughput to improve performance, see the chapter "Advanced Topics".

Streamlining Endpoint Creation

The time required to create and open an endpoint can delay connection set-up time. This can adversely affect servers, especially HTTP servers, since they must manage high connection turnover rates. To handle this problem, follow these guidelines:

• Preallocate endpoints

  Preallocate a pool of open, unbound endpoints into an endpoint cache. When a connection is requested (you receive a T_LISTEN event), you can dequeue an endpoint from this cache and pass it to the function OTAccept.

  Using this method, the only time you have to wait for an endpoint to be created is if the queue is empty, when you must allocate an additional block of endpoints.

• Recycle endpoints

  You can use an endpoint-cache to recycle endpoints when your connection is closed. Rather than call the function OTCloseProvider each time a connection terminates, cache the unbound endpoint. This keeps it available for a subsequent open request.

  To use this method, unbind the endpoint upon receipt of the T_DISCONNECT event. Then, when the notifier receives the T_UNBINDCOMPLETE event, queue that endpoint into your endpoint cache. Optionally, to save memory, you can deallocate the endpoint when the endpoint cache reaches some predetermined limit.

• Create clone configurations

  Another way to speed up endpoint creation is to create a prototype configuration structure with the function OTCreateConfiguration. Then, use the OTCloneConfiguration function to pass the configuration structure to the function OTOpenEndpoint. The call to OTCloneConfiguration is about five times faster than that to the OTCreateConfiguration function.

Handling Dead Clients

A properly designed server should be prepared to handle what happens when a remote client unexpectedly disappears. This problem is further aggravated when the link has been flow-controlled. For example:

1. You are transmitting a large amount of data to a client.

2. Your transport provider enters a flow-control state.

3. The client crashes or becomes unreachable.

4. After a timeout, your server decides to force a disconnect from that client and issues a disconnect request.

5. However the T_DISCONNECT event is subject to flow control, which causes your link to hang.

You can solve this problem by flushing the stream before requesting the disconnection. The best way to do this is to send the I_FLUSH command to the stream head using the OTIoctl function. For example:

#include <stropts.h>

/* check to see if you are already disconnected */

error = OTIoctl(ep, I_FLUSH, (void*) FLUSHRW);
if error OTUnbind(ep)
  .....

MyNotifyProc (... void* the Param) {
   case kStreamIoctlEvent        /* flush is complete */
      (void) OTSndDisconnect (ep, NULL);/* safe to disconnect */
      break;
}

This will result in your notifier receiving all T_MEMORYRELEASED events for any outstanding send calls that acknowledge sends. You should then attempt to send the disconnection request.

Shutting Down Servers

To shut down an Open Transport network server properly, you need to:

• Make sure that all network and I/O operations have either completed or aborted.

• Flush any flow-controlled data streams with the I_FLUSH command. See "Handling Dead Clients" for detailed information.

• Unbind and close all endpoints.

• Cancel any outstanding deferred tasks with the function OTDestroyDeferredTask.

• Release any OTBuffer structures with the function OTReleaseBuffer.

• Dispose of any unused configuration structures with the function OTDestroyConfiguration.

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Subtopics

Streamlining Endpoint Creation

Handling Dead Clients

Shutting Down Servers