How to Spawn a Child Process in Ruby

How do you spawn a child process in Ruby?

You can use the fork kernel method. Here is an example:

#!/usr/bin/env ruby
puts "This is the master process."

child_pid = fork do
  puts "This is the child process"
  exit
end

puts "The PID of the child process is #{child_pid}"

The fork method returns the PID of the process it forks and executes any code in the block passed. Like regular Ruby blocks it keeps the bindings of the parent process.

It is a good idea to make your forked process exit.

Ruby spawn an object method

Just repeating what I said in the comment in an answer, for closure.

since task_start is not a shell script string, but rather a block of code that should be executed asynchronously, use Process.fork { ov.task_start taskid } instead of Process.spawn.

The Process.fork call returns a PID which can be used to stop the process, for example:

# in one terminal
ruby -e "puts Process.fork { loop { puts('tick'); sleep 1 } }"
# it then prints a PID like 20626
# then in another terminal:
kill -9 20626
# the "tick" will stop getting printed every second.

Spawning simultaneous child processes in Ruby

Here:

stdouts=[]
numberOfProcesses.times do 
  stdouts<<PTY.spawn(command_line)[0..-1]
end

That's pretty basic if you just spawn them and get a bunch of STDOUT/STDIN pairs. If you want to be able to work on each process's output as soon as it is done, try this:

threads=[]
numberOfProcesses.times do
  threads<<Thread.new(command_line) |cmd|
    stdout, stdin, pid = PTY.spawn(cmd)
    Process.waitpid(pid)
    process_output(stdout.read)
  end
end
threads.each {|t| t.join}

That spawns them in parallel, each thread waiting for when it's instance is done. When it's instance is done, it processes output and returns. The main thread sits waiting for all of the others to finish.

PID returned by spawn differs from Process.pid of the child process

Looks like the background job operator (&) is causing the intermediate process 1886789. When I remove the background job operator, I get the following output:

Hi parent
93185
Start pid 93185
Bye parent
End pid 93185

Run console command in ruby, get PID of child process and kill it in some seconds

The most appropriate solution looks like this:

parent_pid = Process.spawn("gvim", "file_name_to_open")
# Need to wait in order not to kill process till Gvim is started and visible
sleep(5)  
Process.kill(9, parent_pid)
# Try to get all Gvim PIDs: the result will look like list of PIDs in 
# descending order, so the first one is the last Gvim opened.
all_gvim_pids = `pidof gvim` 
last_gvim_pid = all_gvim_pids.split(' ').map(&:to_i).first
Process.kill(9, last_gvim_pid)

The solution is strange and hacky, but noone has better ideas :(

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