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IPC via named pipe: Difference between revisions
Add Ruby {{in progress}}.
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* Your program may assume it's the sole reader on "in" and the sole writer on "out".
* Read/write operation on pipes are generally blocking. Make your program responsive to both pipes, so that it won't block trying to read the "in" pipe while leaving another process hanging on the other end of "out" pipe indefinitely -- or vice versa. You probably need to either poll the pipes or use multi-threading.
==={{header|Ruby}}===
{{in progress|lang=Ruby|day=30|month=September|year=2011}}
With [[OpenBSD]], we observe that open(2) a named pipe blocks ''all threads'' in a process. (This must be bug in thread library.) So, we fork(2) other process to call open(2), and apply UNIXSocket to send IO object.
<lang ruby>require 'socket'
# Ruby has no direct access to mkfifo(2). We use a shell script.
system 'sh', '-c', <<EOF or abort
test -p in || mkfifo in || exit
test -p out || mkfifo out || exit
EOF
# Forks a process to open _path_. Returns a _socket_ to receive the open
# IO object (by UNIXSocket#recv_io), and the _pid_ of the process.
def open_sesame(path, mode)
reader, writer = UNIXSocket.pair
pid = fork do
begin
reader.close
file = File.open(path, mode)
writer.send_io file
ensure
exit!
end
end
writer.close
return reader, pid
end
insock, inpid = open_sesame("in", "rb")
outsock, outpid = open_sesame("out", "w")
Process.detach(inpid)
Process.detach(outpid)
inpipe, outpipe = nil
count = 0
readers = [insock, outsock]
writers = []
loop do
selection = select(readers, writers)
selection[0].each do |reader|
case reader
when insock
inpipe = reader.recv_io
when outsock
outpipe = reader.recv_io
when inpipe
count += (inpipe.read_nonblock.size rescue 0)
end
end
selection[1].each do |writer|
case writer
when outpipe
outpipe.puts count
exit
end
end
end</lang>
<pre>$ ruby count.rb
count.rb:39:in `recv_io': file descriptor was not passed (msg_controllen=0 smaller than sizeof(struct cmsghdr)=12) (SocketError)
from count.rb:39:in `block (2 levels) in <main>'
from count.rb:36:in `each'
from count.rb:36:in `block in <main>'
from count.rb:34:in `loop'
from count.rb:34:in `<main>'</pre>
{{omit from|GUISS}}
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