在Ruby中並行操作打印輸出而不會混淆輸出的最簡單方法是什麼？

Question

說我分叉了一堆線程，並想從每個線程打印進度輸出到STDERR。我怎樣才能確保輸出保持行原子性，即不會混淆同一輸出行中不同線程的輸出？

# run this a few times and you'll see the problem 
threads = []  
10.times do 
    threads << Thread.new do   
    puts "hello" * 40 
    end  
end 
threads.each {|t| t.join} 

Answer 1

由於可能會從行中單獨寫入新行，因此存在競爭條件。您可以在多線程應用程序中使用看跌期權看到這種噪音：

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

相反，使用print或printf

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

或者，因爲你要寫入STDERR：

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

---

這是Ruby中的錯誤嗎？不是如果評論是作爲標準。這裏是從MRI 1.8.7到2.2.2的IO.puts的定義：

/* 
* call-seq: 
*  ios.puts(obj, ...) => nil 
* 
* Writes the given objects to <em>ios</em> as with 
* <code>IO#print</code>. Writes a record separator (typically a 
* newline) after any that do not already end with a newline sequence. 
* If called with an array argument, writes each element on a new line. 
* If called without arguments, outputs a single record separator. 
* 
*  $stdout.puts("this", "is", "a", "test") 
* 
* <em>produces:</em> 
* 
*  this 
*  is 
*  a 
*  test 
*/