Hello,I'm new to this list and just discovered the existence of libev this morning. So forgive me if this is a FAQ.
It looks like libev is designed to have one thread calling the ev_loop and executing the callbacks (assumed to be fast and never blocking). If it is to be used for a server processing requests, the callbacks would collect the data of the request, and once complete, would queue the request so that worker thread may process it.
This is a straightforward design but it is not performance optimal when requests take a very short time to execute and the system is very loaded (many threads/process). This due to passing the request to another thread for processing. If the system is well loaded, it may take a significant time until the worker thread is given the CPU by the scheduler to process the request.
A more efficient method is the have the callback process the request itself. But some requests may take a long time to execute. So trick is to make the worker threads waiting to be able to monitor. When the monitoring thread detects an event, it signals the worker thread pool, telling them in this way that it is about to leave monitoring activity, and then starts to execute the callback. When done, it goes back into the pool trying to take over monitoring again. If the callback was very fast to execute, there is a good chance that the thread is back to the pool before another thread was given the opportunity by the scheduler to take over monitoring. Otherwise, it waits for its turn to get back to monitoring.
This multi thread model reduces request processing latency and supports callbacks with long time time to execute.
My understanding is that it would simply require the addition of a ev_monitoring() function which would be called by the worker threads. The ev_monitoring() function would return when an event is detected and the information needed to invoke the callback. The ev_monitoring would contain a condition variable used to regulate access to the effective monitoring task.
Some tweaks are required to ensure that there is always at least one thread actively monitoring or ready to take over monitoring. Callbacks should be queued if there is not enough working threads.
I could not see how this could be implemented with the current libev API. Did I miss something ?
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