subprocess模块和multiprocess模块
subprocess模块
subprocess模块允许我们spawn一个新的进程。
>>> subprocess.run(["ls", "-l"]) # doesn't capture output
CompletedProcess(args=['ls', '-l'], returncode=0)
>>> subprocess.run("exit 1", shell=True)
CompletedProcess(args=['ls', '-l'], returncode=0)
如果我们要对创建出来的进程结果进行判断，那我们就需要添加一个check=True的参数。
>>> subprocess.run("exit 1", shell=True, check=True)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib64/python3.9/subprocess.py", line 528, in run
raise CalledProcessError(retcode, process.args,
subprocess.CalledProcessError: Command 'exit 1' returned non-zero exit status 1.
当然，我们使用subprocess.check_x()函数也都会对返回码进行检查，如：subprocess.check_call()、subprocess.check_output()。
实际上，我们在日常中使用频率最高的subprocess.getstatusoutput()函数实际调用的执行函数是subprocess.checkout_output()，而subprocess.checkout_output()调用的执行函数则是subprocess.run(check=True)。
这里针对正常的情况是这样的，但是如果某些进程已经消亡无法跟踪其状态，你在subprocess.check_x()函数时可能就得到不正确的执行结果。
def _internal_poll(self, _deadstate=None, _del_safe=_del_safe):
"""Check if child process has terminated. Returns returncode
attribute.
This method is called by __del__, so it cannot reference anything
outside of the local scope (nor can any methods it calls).
"""
if self.returncode is None:
if not self._waitpid_lock.acquire(False):
# Something else is busy calling waitpid. Don't allow two
# at once. We know nothing yet.
return None
try:
if self.returncode is not None:
return self.returncode # Another thread waited.
pid, sts = _del_safe.waitpid(self.pid, _del_safe.WNOHANG)
if pid == self.pid:
self._handle_exitstatus(sts)
except OSError as e:
if _deadstate is not None:
self.returncode = _deadstate
elif e.errno == _del_safe.ECHILD:
# This happens if SIGCLD is set to be ignored or
# waiting for child processes has otherwise been
# disabled for our process. This child is dead, we
# can't get the status.
# http://bugs.python.org/issue15756
# subprocess.run()函数会执行retcode = process.poll()来返回进程执行结果，但这里如果创建的进程已经死亡了，这里的状态就默认标记为0。
self.returncode = 0
finally:
self._waitpid_lock.release()
return self.returncode
multiprocess模块
multiprocess模块也允许我们创建进程，但这个创建进程类型比subprocess模块更多样，可以支持fork、spawn、forkserver这三种模式。
其他
spawn和fork
spawn进程是创建一个完全资源独立的进程，fork进程是创建一个子进程。
