multithreading - What's the easiest way to print output from parallel operations in Ruby without jumbling up the output? -

say forked of bunch of threads , wants print progress output each 1 stderr. how can in way ensures output retains line-atomicity, i.e. doesn't jumble output different threads in same output line?

# run few times , you'll see problem threads = []     10.times     threads << thread.new             puts "hello" * 40   end      end  threads.each {|t| t.join} 

puts has race condition, since may write new-line separately line. may see sort of noise using puts in multi-threaded application:

thread 0thread 1 thread 0thread 2 thread 1 thread 0thread 3 thread 2 thread 1 

instead, use print or printf

print "thread #{i}" + "\n" print "thread #{i}\n" printf "thread %d\n", 

or, since want write stderr:

$stderr.print "thread #{i}\n" 

---

is bug in ruby? not if comments taken standard. here's definition of io.puts mri 1.8.7 though 2.2.2:

/*  *  call-seq:  *     ios.puts(obj, ...)    => nil  *  *  writes given objects <em>ios</em>  *  <code>io#print</code>. writes record separator (typically  *  newline) after not end newline sequence.  *  if called array argument, writes each element on new line.  *  if called without arguments, outputs single record separator.  *  *     $stdout.puts("this", "is", "a", "test")  *  *  <em>produces:</em>  *  *      *      *      *     test  */