如何在python中对stdout进行原子写入？

Question

我在一些资料中读到print命令不是线程安全的，解决方法是使用系统标准输出写入命令，但它仍然对我不起作用，而且对标准输出的写入不是原子的。在

下面是一个简短的示例（称为这个文件并行实验.py)公司名称：

   import os
   import sys
   from multiprocessing import Pool

   def output(msg):
    msg = '%s%s' % (msg, os.linesep)
    sys.stdout.write(msg)

   def func(input):
    output(u'pid:%d got input \"%s\"' % (os.getpid(), str(input)))

   def executeFunctionInParallel(funcName, inputsList, maxParallelism):
       output(u'Executing function %s on input of size %d with maximum parallelism of %d' % (
           funcName.__name__, len(inputsList), maxParallelism))
       parallelismPool = Pool(processes=maxParallelism)
       executeBooleanResultsList = parallelismPool.map(funcName, inputsList)
       parallelismPool.close()
       output(u'Function %s executed on input of size %d  with maximum parallelism of %d' % (
           funcName.__name__, len(inputsList), maxParallelism))
       # if all parallel executions executed well - the boolean results list should all be True
       return all(executeBooleanResultsList)

   if __name__ == "__main__":
    inputsList=[str(i) for i in range(20)]
    executeFunctionInParallel(func, inputsList, 4)

看看输出：

一、调用python的输出并行实验.py（注意“pid”一词在某些行中弄乱了）：

^{pr2}$

二。调用python的输出并行实验.py>；并行实验.log重定向到意义并行实验.log文件（注意行顺序不好，因为在调用并行调用func的executeFunctionInParallel之前和之后，应该打印一条消息）：

pid:3244 got input "4"
pid:3244 got input "5"
pid:3244 got input "12"
pid:3244 got input "13"
pid:240 got input "0"
pid:240 got input "1"
pid:240 got input "8"
pid:240 got input "9"
pid:240 got input "16"
pid:240 got input "17"
pid:1268 got input "2"
pid:1268 got input "3"
pid:1268 got input "10"
pid:1268 got input "11"
pid:1268 got input "18"
pid:1268 got input "19"
pid:3332 got input "6"
pid:3332 got input "7"
pid:3332 got input "14"
pid:3332 got input "15"
Executing function func on input of size 20 with maximum parallelism of 4
Function func executed on input of size 20  with maximum parallelism of 4

Answer 1

如果您希望避免锁定，并且乐于使用较低级别的接口，那么可以使用os.open，os.write获得POSIX OаAPPEND行为（如果您的系统支持它）；然后查看Is file append atomic in UNIX?。在