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.
I am running Ruby 1.8.7 on an embedded computer that runs linux
I have created a named pipe manually (
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 seconds
(configurable, e.g. 3 of 60):
ticker = Thread.new do
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
ticker.priority += 1
in the main thread the fifo is read:
while input = @raw.gets
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);