[Gambas-user] Opening Pipes (avoiding lockup)

Jussi Lahtinen jussi.lahtinen at gmail.com
Sat Oct 3 22:37:58 CEST 2020

"Opening a pipe for reading normally blocks until some other process opens
the same pipe for writing."

I don't think you should be able to open pipe for read AND write at the
same time.


On Sat, Oct 3, 2020 at 9:56 PM Bruce Steers <bsteers4 at gmail.com> wrote:

> Hi all.
> I just uploaded a simple pipe opening/watching routing to the Application
> section as an example.
> The reason for this was because it took me quite some time to figure out
> how to get a pipe working at first and thought many others may have hit the
> same brick wall. It seemed EVERYTHING I tried just locked up the app til
> the pipe got some text sent, then everything was okay, the app could run
> and the File_Read() event would trigger on any more text sent as expected.
> What was not expected is that "Opening" the pipe is like calling a Read
> method that locks the program till it gets some text.
> I came up with a simple solution (eventually) to use the Shell command to
> echo a blank line to the pipe just before opening it...
>  Shell "echo '' >/tmp/FIFO1"
>  hFile = Pipe "/tmp/FIFO1" For Read Watch
> That way when the pipe opens it gets the echo and moves on so the program
> continues running.
> It just seemed wrong though.
> Like either i was doing something wrong in how i was opening the pipe or
> it was a bug in the pipe opening call?
> I would have thought that setting the "Watch" option would open the pipe
> without expecting text and just set up the Read event and move on.
> I found using "Read Write Watch" all together and setting Blocking to
> False Allowed the program to move past the open without sending text but
> that gave me weird errors like pop-up menus stopped triggering Click()
> events, I had some menus visible in the menubar AND attached to a button
> popup and got the click event okay from the top menu but got nothing from
> the popup menus. If i removed the "Write" from the pipe opening call the
> popups worked again!?
> I found the Shell "echo" method the best way but like i say , seems wrong
> to have to do it that way.
> Thanks all :)
> ----[ http://gambaswiki.org/wiki/doc/netiquette ]----
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