How to block named pipe reading in Ruby?

Question

I am trying to set up a Ruby script that reads from a named pipe in a loop, blocking until input is available in the pipe.

I have a process that periodically places debugging events in a named pipe:

# Open the logging pipe
log = File.open("log_pipe", "w+") #'log_pipe' created in shell using mkfifo
...
# An interesting event happens
log.puts "Interesting event #4291 occurred"
log.flush
...

Then I need a separate process that will read from this channel and print events to the console when they happen. I tried using this code:

input = File.open("log_pipe", "r+") 
while true
  puts input.gets  #I expect this to block and wait for input
end
# Kill loop with ctrl+c when done

I want to input.getsblock, patiently waiting until a new entry arrives at fifo; but instead, he immediately reads niland loops again, scrolling through the top of the console window.

Two things I've tried:

• I opened the fifo input file with both "r" and "r +". I have the same problem anyway:

• , EOF (, , fifo ) - AFAIK .

:

, " " , :

, RGSS, Ruby. , , - , , . Ruby , , ; , . , Ruby , , .

, mkfifo cygwin, , , ; , .

-, irb "":

irb(main):001:0> input = File.open("mypipe", "r")
=> #<File:mypipe>
irb(main):002:0> x = input.gets
=> nil
irb(main):003:0> x = input.gets
=> nil

, input.gets 002 003 - , .

Answer 1

, Cygwin. Windows , Ruby Gem, win32-pipe, .

, , Ruby Gems RGSS script; , win32-pipe, RGSS. , , .

script "" :

module PipeLogger
  # -- Change THIS to change the name of the pipe!
  PIPE_NAME = "RGSSPipe"

  # Constant Defines
  PIPE_DEFAULT_MODE        = 0            # Pipe operation mode
  PIPE_ACCESS_DUPLEX       = 0x00000003   # Pipe open mode
  PIPE_UNLIMITED_INSTANCES = 255          # Number of concurrent instances
  PIPE_BUFFER_SIZE         = 1024         # Size of I/O buffer (1K)
  PIPE_TIMEOUT             = 5000         # Wait time for buffer (5 secs)
  INVALID_HANDLE_VALUE     = 0xFFFFFFFF   # Retval for bad pipe handle

  #-----------------------------------------------------------------------
  # make_APIs
  #-----------------------------------------------------------------------
  def self.make_APIs
    $CreateNamedPipe     = Win32API.new('kernel32', 'CreateNamedPipe', 'PLLLLLLL', 'L')
    $FlushFileBuffers    = Win32API.new('kernel32', 'FlushFileBuffers', 'L', 'B')
    $DisconnectNamedPipe = Win32API.new('kernel32', 'DisconnectNamedPipe', 'L', 'B')
    $WriteFile           = Win32API.new('kernel32', 'WriteFile', 'LPLPP', 'B')
    $CloseHandle         = Win32API.new('kernel32', 'CloseHandle', 'L', 'B')
  end

  #-----------------------------------------------------------------------
  # setup_pipe
  #-----------------------------------------------------------------------
  def self.setup_pipe
    make_APIs
    @@name = "\\\\.\\pipe\\" + PIPE_NAME

    @@pipe_mode = PIPE_DEFAULT_MODE
    @@open_mode = PIPE_ACCESS_DUPLEX
    @@pipe         = nil
    @@buffer       = 0.chr * PIPE_BUFFER_SIZE
    @@size         = 0
    @@bytes        = [0].pack('L')

    @@pipe = $CreateNamedPipe.call(
      @@name,
      @@open_mode,
      @@pipe_mode,
      PIPE_UNLIMITED_INSTANCES,
      PIPE_BUFFER_SIZE,
      PIPE_BUFFER_SIZE,
      PIPE_TIMEOUT,
      0
    )

    if @@pipe == INVALID_HANDLE_VALUE
      # If we could not open the pipe, notify the user
      # and proceed quietly
      print "WARNING -- Unable to create named pipe: " + PIPE_NAME
      @@pipe = nil
    else
      # Prompt the user to open the pipe
      print "Please launch the RGSSMonitor.rb script"
    end
  end

  #-----------------------------------------------------------------------
  # write_to_pipe ('msg' must be a string)
  #-----------------------------------------------------------------------
  def self.write_to_pipe(msg)
    if @@pipe
      # Format data
      @@buffer = msg
      @@size   = msg.size

      $WriteFile.call(@@pipe, @@buffer, @@buffer.size, @@bytes, 0)
    end
  end

  #------------------------------------------------------------------------
  # close_pipe
  #------------------------------------------------------------------------
  def self.close_pipe
    if @@pipe
      # Send kill message to RGSSMonitor
      @@buffer = "!!GAMEOVER!!"
      @@size   = @@buffer.size
      $WriteFile.call(@@pipe, @@buffer, @@buffer.size, @@bytes, 0)

      # Close down the pipe
      $FlushFileBuffers.call(@@pipe)
      $DisconnectNamedPipe.call(@@pipe)
      $CloseHandle.call(@@pipe)
      @@pipe = nil
    end
  end
end

, PipeLogger::setup_pipe, ; PipeLogger::close_pipe . ( "Main" ensure close_pipe.) PipeLogger::write_to_pipe("msg") script string "msg" .

RPG Maker XP; RPG Maker VX .

- . , - Ruby, Ruby Gem win32-pipe script:

require 'rubygems'
require 'win32/pipe'
include Win32

# -- Change THIS to change the name of the pipe!
PIPE_NAME = "RGSSPipe"

Thread.new { loop { sleep 0.01 } } # Allow Ctrl+C

pipe = Pipe::Client.new(PIPE_NAME)
continue = true

while continue
  msg = pipe.read.to_s
  puts msg

  continue = false if msg.chomp == "!!GAMEOVER!!"
end

Ruby 1.8.7 Windows win32-pipe , (. ). "RGSSMonitor.rb" ruby RGSSMonitor.rb.

:

• RGSS, , ; , . , .
• , , , , (, RGSSMonitor.rb). Windows ( 1K), ( " ", ). , RPGXP Ruby script, 10 . ( , RPGVX - .)

Answer 2

, , , EOF , gets nil, .

, - . ( Mac), ( "r" "r+"). , Cygwin (POSIX , FIFO - undefined).

, . IO -, , , , .

input = File.open("log_pipe", "r")      # note 'r', not 'r+'
keep_open = File.open("log_pipe", "w")  # ensure there always a writer
while true
  puts input.gets
end