python - Python `multiprocessing` 中进程的 ident 和 pid 有什么区别？

Question

使用 multiprocessing.Process 创建和启动的进程具有属性 pid(进程 ID)和 ident。 pid 不也是一个标识符吗？这两者有什么区别？

帮助也没有帮助:

 |  ident
 |      Return identifier (PID) of process or `None` if it has yet to start
 |  
 |  pid
 |      Return identifier (PID) of process or `None` if it has yet to start

例子

import multiprocessing
import time


def whatever():
    print("child")
    time.sleep(10)
    print("child done")

created = multiprocessing.Process(target=whatever)
created.start()
time.sleep(1)
print("pid={}".format(created.pid))
print("ident={}".format(created.ident))

在我的例子中，pid == ident。总是这样吗？那可能是特定于操作系统的吗？ (我在 Linux 上运行它。在 Mac/Windows 上会发生什么情况？)

Answer 1

答案在 source code 中.

cpython/Lib/multiprocessing/process.py:

class BaseProcess(object):

    ...

    @property
    def ident(self):
        '''
        Return identifier (PID) of process or `None` if it has yet to start
        '''
        self._check_closed()
        if self is _current_process:
            return os.getpid()
        else:
            return self._popen and self._popen.pid

    pid = ident  # !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

    ...

因此 multiprocessing.Process.pid 只是 multiprocessing.Process.ident 的别名。请注意，multiprocessing.Process 提供了 ident 属性，因此它与 threading.Thread API 兼容。根据documentation :

In addition to the threading.Thread API, Process objects also support the following attributes and methods:

pid - Return the process ID. Before the process is spawned, this will be None.

...