[fpc-devel] ConsoleIO and flushing buffered output

[Michael Van Canneyt]

On Mon, 8 Jun 2020, Christo Crause via fpc-devel wrote:

> Michael, it is entirely possible that I am misunderstanding your
> suggestion, I probably don't grasp the complexities of the RTL texmode IO
> system and also not explaining my intention clearly, for this I apologise.
> Take for example the esp32 unit provided by Florian, here the link between
> the underlying OS output and the RTL is configured by calling OpenIO and
> providing readchar and writechar functions which in turn calls getchar and
> putchar (
> https://github.com/ccrause/freepascal/blob/76911c528251b48e18c348de1758c098ee9fb763/rtl/freertos/xtensa/esp32.pp#L106).
> In this unit Florian uses a custom printpchar procedure which pushes
> characters to the OS and at the end directly calls the OS fflush function.
> This ensures that the haltproc message gets transmitted before the cpu goes
> to sleep.
>
> I'm trying to change the controller unit to use standard RTL write
> functionality, since this gets configured during unit initialization
> anyway. My attempt at "Pascalizing" Florian's version (
> https://github.com/ccrause/freepascal/blob/76911c528251b48e18c348de1758c098ee9fb763/rtl/freertos/xtensa/esp8266.pp#L59)
> calls the normal write functionality and works, except for the last string
> before esp_deep_sleep which doesn't reach the remote terminal.  At the
> moment I fix this by directly calling the OS fflush function.
>
> The only configuration option exposed via consoleio is OpenIO, which
> doesn't have a parameter for a low level flush function.  I could create an
> overloaded OpenIO function with an extra parameter for a flush function
> pointer, and call this, if assigned, at the end of Console_Write.  Is this
> kind of the lower level detail behind your suggestion Michael?

I would add a flushfunc to TUserData and to the OpenIO call in consoleIO:

Type
   TFlushIOFunc = function(UserData: pointer): boolean;

and change
       PUserData = ^TUserData;
       TUserData = record
         WriteChar: TWriteCharFunc;
         ReadChar: TReadCharFunc;
         FlushFunc : TFlushIOFunc;
         UserData: Pointer;
       end;

change
  procedure OpenIO(var f: Text; AWrite: TWriteCharFunc; ARead: TReadCharFunc; AMode: word; AUserData: pointer);
to
  procedure OpenIO(var f: Text; AWrite: TWriteCharFunc; ARead: TReadCharFunc; aFlush : TFlushIOFunc; AMode: word; AUserData: pointer);

and add
   userdata^.FlushFunc := AFlush;

At the end of Console_Write I would call this new flush function:

        if i<>t.BufPos then
           InOutRes:=101
         else
           begin
           if userdata^.FlushFunc(userdata^.UserData) then
             InOutRes:=0
           else
             InOutRes:=101;
           end;
         t.BufPos:=0;
       end;

Console_Write is only called when the internal buffer is full or when the
output must be forced to terminal, so that should be sufficient.

Hope this helps,

Michael.