Date : Nov 5, 2008
Topic : API design, callbacks, implementing inter-process communication
People: James Boston (jboston), Mark Finkle (mfinkle)
15:33 < jboston> mfinkle: http://pastebin.mozilla.org/570000 15:33 < jboston> Wrestling with callbacks. 15:33 < jboston> I'm not sure I can do what I'm trying to do. 15:34 < jboston> I want to get i/o one line at a time. 15:35 < mfinkle> ok, first - how will the i/o actually get put into the callback? 15:35 < mfinkle> I wouldn't worry too much about the callee "getting" the i/o 15:35 < mfinkle> (yet) 15:36 < jboston> Well, I guess all the i/o stuff happens in cpp somewhere in it's own thread. 15:39 < jboston> See, when the process object is created, I'm assuming that it is handling i/o in the background. 15:40 < jboston> Have I got my callbacks backwards? For instance, stdout.getline() would be implemented in cpp. 15:41 < jboston> This is different from having the cpp call the js code when it's ready with something. 15:41 < jboston> Am I talking crazy talk. 15:43 < mfinkle> well, assuming the processes will write to stdout, how will you capture that in c++? 15:43 < mfinkle> some NSPR buffer? 15:44 < jboston> Maybe. I haven't figured that out. 15:44 < jboston> I thought it would go into a queue where I can could retreive one line at a time as needed. 15:45 < mfinkle> jboston: what queue? do you provide one? 15:45 < jboston> I would. 15:46 < mfinkle> ok, so this queue has a datatype? char*, some buffer? 15:46 < jboston> maybe i need stdin = process.getStdIn(); var line = stdin.getline(); 15:46 < jboston> yes. 15:46 < mfinkle> we need to know this so you can make a JS compatible wrapper for the callbacks 15:46 < mfinkle> ID for this queue is needed too 15:47 < mfinkle> do you really need this "line by line" feature? why not just a stream buffer 15:47 < mfinkle> let the caller deal with it 15:48 < jboston> Ok. I think I'm confused somewhere about how this works. I'll have a callback to js code that handles a stream buffer? 15:49 < mfinkle> jboston: first things first 15:49 < mfinkle> does this work at all in NSPR? 15:49 < mfinkle> or do you need to add machinery? 15:50 < jboston> I don't know. 15:50 < mfinkle> then let's not worry about the JS part 15:50 < jboston> Ok. 15:51 < mfinkle> but keep this in mind: callbacks are like events, you could fire it for each line 15:51 < jboston> Ah! 15:51 < mfinkle> buffers would be passed in and not used until the process ends 15:51 < mfinkle> then they could be read in part or in full 15:51 < jboston> Hrm. But what about processes that I expect to run as long as the browser is running. 15:51 < mfinkle> if you think the output could be large, callbacks could be painfully slow 15:52 < jboston> i guess that's the problem i was getting at in my own peculiar way. 15:53 < mfinkle> jboston: consider this - until you know the real implementation details, you might not be able to fire a callback until the process finishes 15:54 < jboston> ok. i've been trying to approch it from high level to low level, but i'm getting lost. i'll take your advice and dive back into the cpp. 15:55 < jboston> You're help is very much appreciated here. You're blog post on callbacks was very informative.