On 11/30/2011 12:59 AM, Hyrum K Wright wrote: > Let me offer a concrete example, in the hopes that I can make some > sense. I use the term "sender" to mean "the thing that is invoking > the editor callbacks" and "receiver" to mean "the thing who is > providing callbacks to be invoked". I believe these are the > traditional uses of the terms; if not, I've got some more reeducation > to go through.
(I've always used "editor driver" and "editor implementation", but whatever.) > In libsvn_client/mergeinfo.c there is a function named > svn_client__elide_mergeinfo_catalog() (or SCEMC for short). SCEMC > uses SDPD to elider mergeinfo and uses a default Ev1 editor with only > custom open_root() and open_directory() handlers[1]. It provides this > editor to SDPD. > > Without the shims, everything works well, but when the delayed-run > action of the shims is inserted, we get crashes. The reason for this > is that with the shims, the SDPD callback is invoked prior to any > open_directory() handlers of the editor are invoked, and the SDPD > callback depends upon state which the open_directory() handler sets. > > Basically, the delayed processing of the Ev1 open_directory() handler > is combined with the *immediate* handling of the SDPD callback, which > results in out-of-order execution of the SDPD callback, and from there > badness ensues. My thought is to move the shim insertion inside SDPD > and make it clever enough to delay calling the SDPD callback until the > Ev1 queue is played back, thus ensuring the ordering is then correct. I guess this is the part where I'm confused. You can't "delay" an open_directory() call -- it must execute, it must return, and when it returns it must provide a new directory baton or throw an error. I'm starting to wonder if these shims fit into a different junction than I'd assumed. In fact, in this case, there should be no shims in use at all -- it's perfectly okay for SCEMC to use SDPD and an Ev1 editor now and forever. We should only be using shims where they are *required* to fix up interface mismatches. No such mismatch exists at this call site which, as you say, owns both the sender and the receiver. Ah... I see what's going on now. You're trying to perform a double transformation (delta->editor->delta) here. Now I understand what you mean by delaying the open_directory(). It's the open_directory() of that tail-end Ev1 that's delayed. So again, in this instance, the use of shims is completely unnecessary. You must know that, so may I assume that you're just trying to do this stuff for the sake of working out problems with the shims themselves? -- C. Michael Pilato <cmpil...@collab.net> CollabNet <> www.collab.net <> Distributed Development On Demand
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