是否有任何python内置模块使用线程？

Question

将导入/使用任何python的内置库产生线程而不被明确询问？

Answer 1

multiprocessing模块和subprocess模块都在内部产生threading.Thead对象以帮助处理它们产生的进程的I/O。

具体来说，multiprocessing.Poolspawns three threads只要你实例化它：

class Pool(object): 
    ''' 
    Class which supports an async version of the `apply()` builtin 
    ''' 
    Process = Process 

    def __init__(self, processes=None, initializer=None, initargs=(), 
       maxtasksperchild=None): 

     ... # Stuff we don't care about 
     self._worker_handler = threading.Thread(
      target=Pool._handle_workers, 
      args=(self,) 
      ) 
     self._worker_handler.daemon = True 
     self._worker_handler._state = RUN 
     self._worker_handler.start() 


     self._task_handler = threading.Thread(
      target=Pool._handle_tasks, 
      args=(self._taskqueue, self._quick_put, self._outqueue, self._pool) 
      ) 
     self._task_handler.daemon = True 
     self._task_handler._state = RUN 
     self._task_handler.start() 

     self._result_handler = threading.Thread(
      target=Pool._handle_results, 
      args=(self._outqueue, self._quick_get, self._cache) 
      ) 
     self._result_handler.daemon = True 
     self._result_handler._state = RUN 
     self._result_handler.start() 

subprocess生成线程when you call popen_object.communicate，从运行子读取标准输出/标准错误。

def _communicate(self, input): 
    stdout = None # Return 
    stderr = None # Return 

    if self.stdout: 
     stdout = [] 
     stdout_thread = threading.Thread(target=self._readerthread, 
             args=(self.stdout, stdout)) 
     stdout_thread.setDaemon(True) 
     stdout_thread.start() 
    if self.stderr: 
     stderr = [] 
     stderr_thread = threading.Thread(target=self._readerthread, 
             args=(self.stderr, stderr)) 
     stderr_thread.setDaemon(True) 
     stderr_thread.start() 

编辑

Mark Dickinson points out该concurrent.futures.ProcessPoolExecutor还产生一个线程，为类似于multiprocessing.Pool原因（处理I/O与产卵过程）：

def _start_queue_management_thread(self): 
    # When the executor gets lost, the weakref callback will wake up 
    # the queue management thread. 
    def weakref_cb(_, q=self._result_queue): 
     q.put(None) 
    if self._queue_management_thread is None: 
     # Start the processes so that their sentinels are known. 
     self._adjust_process_count() 
     self._queue_management_thread = threading.Thread(
       target=_queue_management_worker, 
       args=(weakref.ref(self, weakref_cb), 
         self._processes, 
         self._pending_work_items, 
         self._work_ids, 
         self._call_queue, 
         self._result_queue)) 
     self._queue_management_thread.daemon = True 
     self._queue_management_thread.start() 

Answer 2

下列模块进口threading，表示可以使用“线程”（无论是隐式还是明示）

1. asyncio
2. decimal
3. functools
4. cookiejar
5. multiprocessing
6. queue
7. sched
8. subprocess
9. telnetlib
10. tempfile
11. trace

---

方法论

grep -r "thread" * | grep "import" | grep -v "test" | grep -v "Lib/threading" 

在{python install path}/Lib目录。

使用的方法是查看grep结果中是否出现“线程”，并使用一系列grep来处理结果。

所以拿一点盐的这个答案。