From: Peter Zotov <whitequark@...>
Date: 2013-01-10T07:24:06+09:00
Subject: Re: Illegal seek (Errno::ESPIPE) when reading from named pipe

Maarten Berkel писал 09.01.2013 19:38:
> Hi all,
>
> What is the correct procedure to read one line from a named pipe?
> I tried opening it with f = File.open ; input = f.gets, but that 
> raises
> Errno::ESPIPE (invalid seek) every now and then.
>
> Thanks!
>
> Maarten
>
>
> More info:
>
> I am running Ruby 1.8.7 on an embedded computer that runs linux
> 2.6.35.14.
>
> I have created a named pipe manually (`mkfifo /example/file.fifo`)
>
> I have multiple processes that write into this named pipe and one
> 'reader' process that reads AND also writes into this named pipe.
>
> The reader process opens the pipe like this:
> @raw = File.open(CONFIG["fifo_raw"], File::RDWR)
>
> In a background thread, it writes to the named pipe every <x> seconds
> (configurable, e.g. 3 of 60):
> ticker = Thread.new do
>   while true
>     start_of_this_tick = (Time.now.to_i / rate) * rate
>     start_of_next_tick = start_of_this_tick + rate
>     seconds_to_sleep = start_of_next_tick - Time.now.to_f
>     sleep(seconds_to_sleep) if seconds_to_sleep > 0
>     @raw.write("tick #{start_of_this_tick.to_i}\n")
>   end
> end
> ticker.priority += 1
>
> in the main thread the fifo is read:
> while input = @raw.gets
>    # process input
> end
>
> Every now and then, the gets call raises Errno::ESPIPE (invalid 
> seek). I
> have also tried readline, with the same behavior.
>
> My impression is that I have to explicitly 'tell' ruby that this file 
> is
> a pipe instead of a regular file and that it cannot be seeked. In 
> io.c I
> found that there is a method rb_io_getline_fast which seems to be
> buffering and seeking in appendline:
> fread(RSTRING(str)->ptr + last, 1, pending, f);

Try IO#sysread.

-- 
   WBR, Peter Zotov.