Transport disembark #4220
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Transport disembark #4220
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…y once This allows to re-use http1_new_session from custom implementations, in that it can serve as an entry point into the state machine also for existing sessions (without requiting 8 bytes of session workspace for each request served).
This allows code-reuse from custom implementations where only the deliver deliver callback differs.
This is in preparation of simplifications and to be able disembark during delivery.
now that boc lives in struct req, it is obsolete also change some subordinate helper functions
To prepare for the next commit, we introduce a new finish step to the request FSM, which is just the former tail of cnt_transmit().
This allows the transport's delivery function to disembark the thread by returning VTR_D_DISEMBARK. In this case, CNT_Request() needs to be called at a later time to continue. It is the vtr_deliver_f's responsibility to clear req->wrk because only it can ensure proper synchronization with another thread which might already be running.
vmod_debug_transports.c demonstrates the basic mechanics of disembarking a request from the vrt_deliver_f, delivering a body from another worker and finishing the request.
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This is the next chapter of the book of AI, see #4209
To eventually get to event driven, asynchronous IO where a smaller number of threads handles a large number of requests, we also need a way to disembark a request from a worker and have another thread pick up where it left of, then reentering the state machine later to finish off.
Thanks to the already existing disembark facility used for waitinglist wakeups, implementing this is pretty straight forward: We basically only need to allow the vtr_deliver_f (transport deliver function) to tell the state engine to disembark, add a "finish" state, and everything else more or less works out of the box.
The last commit has a demonstration in a test case.
Everything else in this patch is refactoring.