[tcf-dev] Problem with ZeroCopy and flushing in TCF agent

[Patrick Tasse <patrick.tasse@xxxxxxxxx>]

Hi,

I am working on an agent plugin that requires the ZeroCopy service to be enabled in the TCF agent.

It writes an Event message to the channel's output stream using write_stream() for some message parameters and json_splice_binary_offset() for the binary data in the message. This method then performs a zero-copy splice.

The calling thread must be assured that the message is sent and that the zero-copied binary data is no longer needed before continuing. In previous code (which was based on an older version of TCF), it was calling the flush_stream() method, but this method does not exist anymore (instead, if I understand correctly, Event messages are automatically flushed once we write MARKER_EOM to the output stream).

However, the flushing mechanism in channel_tcp.c is to post a tcp_flush_event to the channel's event thread. The write_stream(out, MARKER_EOM) method can return before the flushing is even started. Therefore, the zero-copied binary data can be overwritten before the message is sent, and the TCF channel on the other side receives a corrupt message.

Is there a mechanism that an agent plugin could use to block until, or be notified that the flushing has completed?

If there is none, I could help to write and test a patch for it. But I would need advice on how it should be designed.

Thanks,
Patrick

(by the way the link to the tcf-dev mailing list is not working on this page: http://www.eclipse.org/projects/project_summary.php?projectid=tools.cdt.tcf)