popen_thread_example.rb

require "thread"

# This is an example of how to use popen in a nonblocking fashion while
# consuming the output and manipulating it slightly. Additionally it ensures
# that the output maintains some consistency even with interleaving writes.

# Make a mutex so that we only let one thing write to stdout at a time
@stdout_mutex = Mutex.new

# A version of puts which shows some debug information, handy for showing off
# some thread stuff.
def debug_puts(message)
  safe_puts "%20s %10i %s" % [Thread.current, Time.now.to_i, message]
end

# A version of puts that will not intermingle output with other threads.
def safe_puts(message)
  @stdout_mutex.synchronize do # will wait if another thread is already executing
    puts message
  end
end

# Open a new thread, save it, and run a long running command.
process_thread = Thread.new do
  IO.popen("echo hello; sleep 10; echo goodbye") do |process|
    debug_puts process.gets
    debug_puts process.gets
  end
end

# Do normal main thread stuff!
debug_puts "Main thread doing it's thang!"
sleep 1

# How to wait for the thread to end on it's own
debug_puts "Ok, Main thread all done, I want to wait until child thread is ready..."
process_thread.join

debug_puts "Everyone is done"