On Fri, Sep 23, 2011 at 4:32 AM, Kristian Nielsen <kniel...@knielsen-hq.org> wrote: > MARK CALLAGHAN <mdcal...@gmail.com> writes: > >> Why does this need to save/restore thread contexts (setcontext, etc)? >> I think that if the library is that hard to change then it should be >> fixed or a simpler solution should be attempted. > > In general, when implementing non-blocking semantics like this, there are two > main approaches: > > 1. Write the code in event-driven style. This means using some kind of state > machine or message passing (or both) rather than normal nested > calls. Whenever code needs to do I/O, or call another function that might > do I/O, the current state is manually saved to some struct and control > returns to the caller. When the I/O completes control must continue in the > next state of the state machine or handler of completion message. > > 2. Use co-routines (also called fibers or light-weight threads or > whatever). The code is written in normal style with nested calls. For > operations that need to do I/O, a co-routine is spawned to run the > operation; when waiting for I/O the co-routine is suspended, and resumed > again when I/O completes. > > The main reason I choose (2) is similar to what RethinkDB describe here: > > http://blog.rethinkdb.com/improving-a-large-c-project-with-coroutines > http://blog.rethinkdb.com/making-coroutines-fast > > Basically, (1) is nice for writing quick IRC bots and the like, but as the > complexity of the problem grows, the event-driven code becomes very hard to > maintain and extend. > > For adding non-blocking to an existing library like libmysql, there is the > added advantage that the change can be much less intrusive, as we can avoid > re-writing parts of the existing code into event-driven style.
Why isn't it sufficient to do a sequence of non-blocking reads to buffer enough data to produce a query result and then process the received data? That doesn't require getcontext/setcontext. -- Mark Callaghan mdcal...@gmail.com _______________________________________________ Mailing list: https://launchpad.net/~maria-developers Post to : maria-developers@lists.launchpad.net Unsubscribe : https://launchpad.net/~maria-developers More help : https://help.launchpad.net/ListHelp
