On Mon, 10 May 2010 14:23:05 +0200 Jan Kiszka <jan.kis...@web.de> wrote:
> Markus Armbruster wrote: > > Jan Kiszka <jan.kis...@web.de> writes: > > > >> Markus Armbruster wrote: > >>> Jan Kiszka <jan.kis...@web.de> writes: > >>> > >>>> Luiz, > >>>> > >>>> I missed this when the API was first proposed: > >>>> > >>>> cur_mon is scheduled for removal (one day...). It's just an intermediate > >>>> step to convert all users to explicit 'mon' passing. Thus, new APIs > >>>> should not rely it. > >>>> > >>>> I just realized that monitor_cur_is_qmp() does so. It should be > >>>> refactored to monitor_is_qmp(Monitor *mon). And qerror should be enhance > >>>> by a 'mon' argument as well. Callers that aren't passed a 'mon' > >>>> themselves should either be fixed at this chance or could fall back to > >>>> cur_mon for the time being. > >>>> > >>>> So far for the theory - do you see any pitfalls in the existing usage? > >>> I put in the new uses of cur_mon, Luiz "only" ACKed them. > >>> > >>> At any point in the program execution, we have one current monitor, or > >>> none. Passing around the current monitor within monitor code is > >>> workable, if somewhat tedious. But we need it not just in monitor code, > >>> we need it anywhere where we report errors. In other words, pretty much > >>> everywhere. Including places that do not and should not know about the > >>> monitor. Handing a monitor parameter down pretty much every call chain > >>> is beyond tedious, it's impractical. > >> It's a process, but I don't think it's impractical per se. > >> > >>> The code reporting an error generally does not and should not know > >>> anything about *how* the error gets communicated to the user. > >>> Insulating it from that detail is proper separation of concerns, and > >>> global variable cur_mon is my tool to get it. Good software > >>> engineering. Like many powerful tools, global variables should be used > >>> sparingly and with care. I feel this use is well justified. > >>> > >>> Instead of eliminating cur_mon, I'd like it to be hidden within > >>> monitor.c. There are a few uses left outside it. > >> If we start to allow cur_mon for error reporting, there is no reason not > >> to convert monitor_printf back to where it came from. Back then we > >> agreed on the current path. If we now decide to roll back, then let's > >> make it consistently. > > > > Makes sense. > > > >> But we already refactored quite a lot of code for > >> explicit monitor passing... > >> > >> Jan > >> > >> PS: A patch for establishing monitor_is_qmp is in my queue. Holding it > >> back for now until we agreed how to proceed. > > > > monitor_is_qmp() is used only in a few places. The real troublemakers > > are error_report() & friends, and qerror_report(). These are all over > > the place, with more to come. > > Right, therefore we need a quick decision avoid introducing more > [q]error_report users without mon if cur_mon shall not stay. I knew there were problems with cur_mon, but I agree with Markus that functions like error reporting ones should not know where the output is going to. But I feel I didn't spend much time trying to understand the problems with cur_mon, how unreliable is it?
