On Mon, Jun 8, 2020 at 12:15 PM Tomas Hajny <xhaj...@hajny.biz> wrote:
> On 2020-06-08 11:39, Michael Van Canneyt wrote: > > On Mon, 8 Jun 2020, Christo Crause via fpc-devel wrote: > . > . > >> Thanks for your response Michael. Using InOutFunc to also flush the > >> output > >> buffer will work, but that seems inefficient, since the flush needs to > >> wait > >> until the transmit buffer is empty (at slow UART speeds this could > >> potentially take several ms to complete). Is there a specific reason > >> why > >> the RTL Flush procedure does not call the FlushFunc method? > > > > I checked; That code is so old, no idea. > > > > From what I can see the flush code could be changed to > > > > if Assigned((TextRec(t).FlushFunc) then > > FileFunc(TextRec(t).FlushFunc)(TextRec(t)) > > else > > FileFunc(TextRec(t).InOutFunc)(TextRec(t)); > > > > But keep in mind that the InoutFunc() is only called when actually > > writing > > data, meaning: when the internal text buffer is full or on a terminal > > with > > every writeln(), so I don't think it is inefficient. Writeln() will do > > a > > flush. Whether this happens in .InOutFunc or .FlushFunc is largely > > irrelevant. > > The question is whether the potential change would make any difference. > IMHO, the important points are: > > 1) The point of flushing is making sure the I/O is really performed (the > data are sent to the operating system _and_ flushed from internal > buffers of the underlying operating system / platform). Doing the latter > without the former makes no sense. > > 2) From semantic point of view, all data should be sent to the final > place (block device / console / ...) before the call to Flush is > finished (otherwise the following actions may have incorrect results - > the program might finish before all data are transmitted, other I/O may > be invoked, etc.). > > From this point of view, the proposed change would only lead to code > duplication between FlushFunc and InOutFunc and / or to increased code - > e.g. checking FlushFunc being nil before calling InOutFunc just to call > InOutFunc (or to perform functionality currently included in InOutFunc) > from within FlushFunc anyway. > <https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel> Tomas and Michael, thank you for this discussion. I'm starting to think the use case I'm considering is perhaps not covered by the current design. At the moment I directly call the OS flush function before putting the cpu to sleep and that works; I was just wondering if there is a Pascal way to accomplish this so that a user doesn't have to remember to call a nonstandard function when a Flush function already exist in the RTL.
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