asyncioシリーズ二、asyncioサブプロセス

asyncioのサブプロセス
公式サイト接続:https://docs.python.org/zh-cn/3.7/library/asyncio-subprocess.html
 
公式サイトの例:
 

import asyncio

async def run(cmd):
    proc = await asyncio.create_subprocess_shell(
        cmd,
        stdout=asyncio.subprocess.PIPE,
        stderr=asyncio.subprocess.PIPE)

    stdout, stderr = await proc.communicate()

    print(f'[{cmd!r} exited with {proc.returncode}]')
    if stdout:
        print(f'[stdout]
{stdout.decode()}')
    if stderr:
        print(f'[stderr]
{stderr.decode()}')

asyncio.run(run('ls /zzz'))

実行結果:
 

['ls /zzz' exited with 1]
[stderr]
ls: /zzz: No such file or directory

一、サブプロセスの作成
coroutine  asyncio. create_subprocess_exec (program, *args, stdin=None, stdout=None, stderr=None, loop=None, limit=None, **kwds)
サブプロセスを作成します.
The limit argument sets the buffer limit for  StreamReader  wrappers for  Process.stdout  and  Process.stderr  (if  subprocess.PIPE  is passed to stdout and stderr arguments).
Return a  Process  instance.
See the documentation of  loop.subprocess_exec()  for other parameters.
プロセスインスタンスを返します.
 
coroutine  asyncio. create_subprocess_shell (cmd, stdin=None, stdout=None, stderr=None, loop=None, limit=None, **kwds)
Run the cmd shell command.
The limit argument sets the buffer limit for  StreamReader  wrappers for  Process.stdout  and  Process.stderr  (if  subprocess.PIPE  is passed to stdout and stderr arguments).
Return a  Process  instance.
See the documentation of  loop.subprocess_shell()  for other parameters.
 
重要
 
It is the application's responsibility to ensure that all whitespace and special characters are quoted appropriately to avoid shell injection vulnerabilities. The  shlex.quote()  function can be used to properly escape whitespace and special shell characters in strings that are going to be used to construct shell commands.
 
注釈
 
The default asyncio event loop implementation on Windows does not support subprocesses. Subprocesses are available for Windows if a  ProactorEventLoop  is used. See Subprocess Support on Windows for details.
Windowsシステムは異なるモジュールを実現しています.
 
参照
 
asyncio also has the following low-level APIs to work with subprocesses:  loop.subprocess_exec() , loop.subprocess_shell() ,  loop.connect_read_pipe() ,  loop.connect_write_pipe() , as well as the Subprocess Transports and Subprocess Protocols.
 
属性:asyncio.subprocess. PIPE
Can be passed to the stdin, stdout or stderr parameters.
If PIPE is passed to stdin argument, the  Process.stdin  attribute will point to a  StreamWriter  instance.
If PIPE is passed to stdout or stderr arguments, the  Process.stdout  and  Process.stderr  attributes will point to  StreamReader  instances.
この属性がstdinパラメータに伝達されると、Process.stdinプロパティは、StreamWriterインスタンスを指します.
  asyncio.subprocess. STDOUT
Special value that can be used as the stderr argument and indicates that standard error should be redirected into standard output.
stderrのパラメータとして使用できます.stderrはstdoutに指向します.
  asyncio.subprocess. DEVNULL
Special value that can be used as the stdin, stdout or stderr argument to process creation functions. It indicates that the special file  os.devnull  will be used for the corresponding subprocess stream. os.devnullが対応するストリームに呼び出されるstdin,stdout,stderrとして使用することができる.
 
二、Subprocessescreate_subprocess_exec() and create_subprocess_shell()はsubprocessesのインスタンスを返します
 
coroutine  wait ()
Wait for the child process to terminate.
Set and return the  returncode  attribute.
サブプロセスの終了を待ってreturncodeを返します.
注釈
 
This method can deadlock when using  stdout=PIPE  or  stderr=PIPE  and the child process generates so much output that it blocks waiting for the OS pipe buffer to accept more data. Use the communicate()  method when using pipes to avoid this condition.
  stdout=PIPEまたはstderr=PIPEで、サブプロセスがosパイプのキャッシュをブロックする大量のデータを生成すると、デッドロックが発生します.communicate()メソッドを使用すると回避できます.
 
coroutine  communicate (input=None)
Interact with process:

send data to stdin (if input is not  None );

read data from stdout and stderr, until EOF is reached;

wait for process to terminate.

The optional input argument is the data ( bytes  object) that will be sent to the child process.
Return a tuple  (stdout_data, stderr_data) .
If either  BrokenPipeError  or  ConnectionResetError  exception is raised when writing input into stdin, the exception is ignored. This condition occurs when the process exits before all data are written into stdin.
If it is desired to send data to the process' stdin, the process needs to be created with  stdin=PIPE . Similarly, to get anything other than  None  in the result tuple, the process has to be created with  stdout=PIPE  and/or  stderr=PIPE  arguments.
Note, that the data read is buffered in memory, so do not use this method if the data size is large or unlimited.
機能:入力にデータを送信し、出力から読み、プロセスの終了を待つ.
戻り:(標準出力、標準エラー出力)
BrokenPipeErrorとConnectResetErrorが現れたのは、プロセスが終了したためだと述べた.
メモリにキャッシュされますが、データ量が大きすぎる場合は使用しません.
  send_signal (signal)
Sends the signal signal to the child process.
  terminate ()
Stop the child process.
On POSIX systems this method sends  signal.SIGTERM  to the child process.
  kill ()
Kill the child.
On POSIX systems this method sends  SIGKILL  to the child process.
  stdin
Standard input stream ( StreamWriter ) or  None  if the process was created with  stdin=None .
  stdout
Standard output stream ( StreamReader ) or  None  if the process was created with  stdout=None .
  stderr
Standard error stream ( StreamReader ) or  None  if the process was created with  stderr=None .
  pid
Process identification number (PID).
Note that for processes created by the  create_subprocess_shell()  function, this attribute is the PID of the spawned shell.
PIDを返します.
  returncode
Return code of the process when it exits.
A  None  value indicates that the process has not terminated yet.
負の値-Nは、信号Nによってサブプロセスが中断することを示す(POSIXのみ).
終了コードを返します.終了しなければNoneを返します.
 
三、Subprocess and Threads
Standard asyncio event loop supports running subprocesses from different threads, but there are limitations:

An event loop must run in the main thread.

The child watcher must be instantiated in the main thread before executing subprocesses from other threads. Call the  get_child_watcher()  function in the main thread to instantiate the child watcher.

asyncioイベントループは、異なるスレッドで使用できます.しかし、2つの制限があります.
1、メインスレッドでイベントループを実行する必要があります.
2.サブスレッドのモニタは、サブスレッドが実行される前にメインスレッドでインスタンス化する必要があります.get_を使うことができますchild_watcherメソッド.
参照
The Concurrency and multithreading in asyncio section.
 
公式サイトの例:
 

import asyncio
import sys

async def get_date():
    code = 'import datetime; print(datetime.datetime.now())'

    # Create the subprocess; redirect the standard output
    # into a pipe.
    proc = await asyncio.create_subprocess_exec(
        sys.executable, '-c', code,
        stdout=asyncio.subprocess.PIPE)

    # Read one line of output.
    data = await proc.stdout.readline()
    line = data.decode('ascii').rstrip()

    # Wait for the subprocess exit.
    await proc.wait()
    return line

if sys.platform == "win32":
    asyncio.set_event_loop_policy(
        asyncio.WindowsProactorEventLoopPolicy())

date = asyncio.run(get_date())
print(f"Current date: {date}")