420 lines
15 KiB
ReStructuredText
420 lines
15 KiB
ReStructuredText
.. currentmodule:: asyncio
|
|
|
|
.. _asyncio-subprocess:
|
|
|
|
Subprocess
|
|
==========
|
|
|
|
Windows event loop
|
|
------------------
|
|
|
|
On Windows, the default event loop is :class:`SelectorEventLoop` which does not
|
|
support subprocesses. :class:`ProactorEventLoop` should be used instead.
|
|
Example to use it on Windows::
|
|
|
|
import asyncio, sys
|
|
|
|
if sys.platform == 'win32':
|
|
loop = asyncio.ProactorEventLoop()
|
|
asyncio.set_event_loop(loop)
|
|
|
|
.. seealso::
|
|
|
|
:ref:`Available event loops <asyncio-event-loops>` and :ref:`Platform
|
|
support <asyncio-platform-support>`.
|
|
|
|
|
|
Create a subprocess: high-level API using Process
|
|
-------------------------------------------------
|
|
|
|
.. coroutinefunction:: create_subprocess_exec(\*args, stdin=None, stdout=None, stderr=None, loop=None, limit=None, \*\*kwds)
|
|
|
|
Create a subprocess.
|
|
|
|
The *limit* parameter sets the buffer limit passed to the
|
|
:class:`StreamReader`. See :meth:`BaseEventLoop.subprocess_exec` for other
|
|
parameters.
|
|
|
|
Return a :class:`~asyncio.subprocess.Process` instance.
|
|
|
|
This function is a :ref:`coroutine <coroutine>`.
|
|
|
|
.. coroutinefunction:: create_subprocess_shell(cmd, stdin=None, stdout=None, stderr=None, loop=None, limit=None, \*\*kwds)
|
|
|
|
Run the shell command *cmd*.
|
|
|
|
The *limit* parameter sets the buffer limit passed to the
|
|
:class:`StreamReader`. See :meth:`BaseEventLoop.subprocess_shell` for other
|
|
parameters.
|
|
|
|
Return a :class:`~asyncio.subprocess.Process` instance.
|
|
|
|
It is the application's responsibility to ensure that all whitespace and
|
|
metacharacters are quoted appropriately to avoid `shell injection
|
|
<https://en.wikipedia.org/wiki/Shell_injection#Shell_injection>`_
|
|
vulnerabilities. The :func:`shlex.quote` function can be used to properly
|
|
escape whitespace and shell metacharacters in strings that are going to be
|
|
used to construct shell commands.
|
|
|
|
This function is a :ref:`coroutine <coroutine>`.
|
|
|
|
Use the :meth:`BaseEventLoop.connect_read_pipe` and
|
|
:meth:`BaseEventLoop.connect_write_pipe` methods to connect pipes.
|
|
|
|
|
|
Create a subprocess: low-level API using subprocess.Popen
|
|
---------------------------------------------------------
|
|
|
|
Run subprocesses asynchronously using the :mod:`subprocess` module.
|
|
|
|
.. coroutinemethod:: BaseEventLoop.subprocess_exec(protocol_factory, \*args, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE, \*\*kwargs)
|
|
|
|
Create a subprocess from one or more string arguments (character strings or
|
|
bytes strings encoded to the :ref:`filesystem encoding
|
|
<filesystem-encoding>`), where the first string
|
|
specifies the program to execute, and the remaining strings specify the
|
|
program's arguments. (Thus, together the string arguments form the
|
|
``sys.argv`` value of the program, assuming it is a Python script.) This is
|
|
similar to the standard library :class:`subprocess.Popen` class called with
|
|
shell=False and the list of strings passed as the first argument;
|
|
however, where :class:`~subprocess.Popen` takes a single argument which is
|
|
list of strings, :func:`subprocess_exec` takes multiple string arguments.
|
|
|
|
The *protocol_factory* must instanciate a subclass of the
|
|
:class:`asyncio.SubprocessProtocol` class.
|
|
|
|
Other parameters:
|
|
|
|
* *stdin*: Either a file-like object representing the pipe to be connected
|
|
to the subprocess's standard input stream using
|
|
:meth:`~BaseEventLoop.connect_write_pipe`, or the constant
|
|
:const:`subprocess.PIPE` (the default). By default a new pipe will be
|
|
created and connected.
|
|
|
|
* *stdout*: Either a file-like object representing the pipe to be connected
|
|
to the subprocess's standard output stream using
|
|
:meth:`~BaseEventLoop.connect_read_pipe`, or the constant
|
|
:const:`subprocess.PIPE` (the default). By default a new pipe will be
|
|
created and connected.
|
|
|
|
* *stderr*: Either a file-like object representing the pipe to be connected
|
|
to the subprocess's standard error stream using
|
|
:meth:`~BaseEventLoop.connect_read_pipe`, or one of the constants
|
|
:const:`subprocess.PIPE` (the default) or :const:`subprocess.STDOUT`.
|
|
By default a new pipe will be created and connected. When
|
|
:const:`subprocess.STDOUT` is specified, the subprocess's standard error
|
|
stream will be connected to the same pipe as the standard output stream.
|
|
|
|
* All other keyword arguments are passed to :class:`subprocess.Popen`
|
|
without interpretation, except for *bufsize*, *universal_newlines* and
|
|
*shell*, which should not be specified at all.
|
|
|
|
Returns a pair of ``(transport, protocol)``, where *transport* is an
|
|
instance of :class:`BaseSubprocessTransport`.
|
|
|
|
This method is a :ref:`coroutine <coroutine>`.
|
|
|
|
See the constructor of the :class:`subprocess.Popen` class for parameters.
|
|
|
|
.. coroutinemethod:: BaseEventLoop.subprocess_shell(protocol_factory, cmd, \*, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE, \*\*kwargs)
|
|
|
|
Create a subprocess from *cmd*, which is a character string or a bytes
|
|
string encoded to the :ref:`filesystem encoding <filesystem-encoding>`,
|
|
using the platform's "shell" syntax. This is similar to the standard library
|
|
:class:`subprocess.Popen` class called with ``shell=True``.
|
|
|
|
The *protocol_factory* must instanciate a subclass of the
|
|
:class:`asyncio.SubprocessProtocol` class.
|
|
|
|
See :meth:`~BaseEventLoop.subprocess_exec` for more details about
|
|
the remaining arguments.
|
|
|
|
Returns a pair of ``(transport, protocol)``, where *transport* is an
|
|
instance of :class:`BaseSubprocessTransport`.
|
|
|
|
It is the application's responsibility to ensure that all whitespace and
|
|
metacharacters are quoted appropriately to avoid `shell injection
|
|
<https://en.wikipedia.org/wiki/Shell_injection#Shell_injection>`_
|
|
vulnerabilities. The :func:`shlex.quote` function can be used to properly
|
|
escape whitespace and shell metacharacters in strings that are going to be
|
|
used to construct shell commands.
|
|
|
|
This method is a :ref:`coroutine <coroutine>`.
|
|
|
|
.. seealso::
|
|
|
|
The :meth:`BaseEventLoop.connect_read_pipe` and
|
|
:meth:`BaseEventLoop.connect_write_pipe` methods.
|
|
|
|
|
|
Constants
|
|
---------
|
|
|
|
.. data:: asyncio.subprocess.PIPE
|
|
|
|
Special value that can be used as the *stdin*, *stdout* or *stderr* argument
|
|
to :func:`create_subprocess_shell` and :func:`create_subprocess_exec` and
|
|
indicates that a pipe to the standard stream should be opened.
|
|
|
|
.. data:: asyncio.subprocess.STDOUT
|
|
|
|
Special value that can be used as the *stderr* argument to
|
|
:func:`create_subprocess_shell` and :func:`create_subprocess_exec` and
|
|
indicates that standard error should go into the same handle as standard
|
|
output.
|
|
|
|
.. data:: asyncio.subprocess.DEVNULL
|
|
|
|
Special value that can be used as the *stdin*, *stdout* or *stderr* argument
|
|
to :func:`create_subprocess_shell` and :func:`create_subprocess_exec` and
|
|
indicates that the special file :data:`os.devnull` will be used.
|
|
|
|
|
|
Process
|
|
-------
|
|
|
|
.. class:: asyncio.subprocess.Process
|
|
|
|
A subprocess created by the :func:`create_subprocess_exec` or the
|
|
:func:`create_subprocess_shell` function.
|
|
|
|
The API of the :class:`~asyncio.subprocess.Process` class was designed to be
|
|
close to the API of the :class:`subprocess.Popen` class, but there are some
|
|
differences:
|
|
|
|
* There is no explicit :meth:`~subprocess.Popen.poll` method
|
|
* The :meth:`~subprocess.Popen.communicate` and
|
|
:meth:`~subprocess.Popen.wait` methods don't take a *timeout* parameter:
|
|
use the :func:`wait_for` function
|
|
* The *universal_newlines* parameter is not supported (only bytes strings
|
|
are supported)
|
|
* The :meth:`~asyncio.subprocess.Process.wait` method of
|
|
the :class:`~asyncio.subprocess.Process` class is asynchronous whereas the
|
|
:meth:`~subprocess.Popen.wait` method of the :class:`~subprocess.Popen`
|
|
class is implemented as a busy loop.
|
|
|
|
This class is :ref:`not thread safe <asyncio-multithreading>`. See also the
|
|
:ref:`Subprocess and threads <asyncio-subprocess-threads>` section.
|
|
|
|
.. coroutinemethod:: wait()
|
|
|
|
Wait for child process to terminate. Set and return :attr:`returncode`
|
|
attribute.
|
|
|
|
This method is a :ref:`coroutine <coroutine>`.
|
|
|
|
.. note::
|
|
|
|
This will deadlock when using ``stdout=PIPE`` or ``stderr=PIPE`` and
|
|
the child process generates enough output to a pipe such that it
|
|
blocks waiting for the OS pipe buffer to accept more data. Use the
|
|
:meth:`communicate` method when using pipes to avoid that.
|
|
|
|
.. coroutinemethod:: communicate(input=None)
|
|
|
|
Interact with process: Send data to stdin. Read data from stdout and
|
|
stderr, until end-of-file is reached. Wait for process to terminate.
|
|
The optional *input* argument should be data to be sent to the child
|
|
process, or ``None``, if no data should be sent to the child. The type
|
|
of *input* must be bytes.
|
|
|
|
:meth:`communicate` returns a tuple ``(stdout_data, stderr_data)``.
|
|
|
|
If a :exc:`BrokenPipeError` or :exc:`ConnectionResetError` exception is
|
|
raised when writing *input* into stdin, the exception is ignored. It
|
|
occurs when the process exits before all data are written into stdin.
|
|
|
|
Note that if you want to send data to the process's stdin, you need to
|
|
create the Process object with ``stdin=PIPE``. Similarly, to get anything
|
|
other than ``None`` in the result tuple, you need to give ``stdout=PIPE``
|
|
and/or ``stderr=PIPE`` too.
|
|
|
|
This method is a :ref:`coroutine <coroutine>`.
|
|
|
|
.. note::
|
|
|
|
The data read is buffered in memory, so do not use this method if the
|
|
data size is large or unlimited.
|
|
|
|
.. versionchanged:: 3.4.2
|
|
The method now ignores :exc:`BrokenPipeError` and
|
|
:exc:`ConnectionResetError`.
|
|
|
|
.. method:: send_signal(signal)
|
|
|
|
Sends the signal *signal* to the child process.
|
|
|
|
.. note::
|
|
|
|
On Windows, :py:data:`SIGTERM` is an alias for :meth:`terminate`.
|
|
``CTRL_C_EVENT`` and ``CTRL_BREAK_EVENT`` can be sent to processes
|
|
started with a *creationflags* parameter which includes
|
|
``CREATE_NEW_PROCESS_GROUP``.
|
|
|
|
.. method:: terminate()
|
|
|
|
Stop the child. On Posix OSs the method sends :py:data:`signal.SIGTERM`
|
|
to the child. On Windows the Win32 API function
|
|
:c:func:`TerminateProcess` is called to stop the child.
|
|
|
|
.. method:: kill()
|
|
|
|
Kills the child. On Posix OSs the function sends :py:data:`SIGKILL` to
|
|
the child. On Windows :meth:`kill` is an alias for :meth:`terminate`.
|
|
|
|
.. attribute:: stdin
|
|
|
|
Standard input stream (:class:`StreamWriter`), ``None`` if the process
|
|
was created with ``stdin=None``.
|
|
|
|
.. attribute:: stdout
|
|
|
|
Standard output stream (:class:`StreamReader`), ``None`` if the process
|
|
was created with ``stdout=None``.
|
|
|
|
.. attribute:: stderr
|
|
|
|
Standard error stream (:class:`StreamReader`), ``None`` if the process
|
|
was created with ``stderr=None``.
|
|
|
|
.. warning::
|
|
|
|
Use the :meth:`communicate` method rather than :attr:`.stdin.write
|
|
<stdin>`, :attr:`.stdout.read <stdout>` or :attr:`.stderr.read <stderr>`
|
|
to avoid deadlocks due to streams pausing reading or writing and blocking
|
|
the child process.
|
|
|
|
.. attribute:: pid
|
|
|
|
The identifier of the process.
|
|
|
|
Note that for processes created by the :func:`create_subprocess_shell`
|
|
function, this attribute is the process identifier of the spawned shell.
|
|
|
|
.. attribute:: returncode
|
|
|
|
Return code of the process when it exited. A ``None`` value indicates
|
|
that the process has not terminated yet.
|
|
|
|
A negative value ``-N`` indicates that the child was terminated by signal
|
|
``N`` (Unix only).
|
|
|
|
|
|
.. _asyncio-subprocess-threads:
|
|
|
|
Subprocess and threads
|
|
----------------------
|
|
|
|
asyncio supports running subprocesses from different threads, but there
|
|
are limits:
|
|
|
|
* 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 :func:`get_child_watcher`
|
|
function in the main thread to instantiate the child watcher.
|
|
|
|
The :class:`asyncio.subprocess.Process` class is not thread safe.
|
|
|
|
.. seealso::
|
|
|
|
The :ref:`Concurrency and multithreading in asyncio
|
|
<asyncio-multithreading>` section.
|
|
|
|
|
|
Subprocess examples
|
|
-------------------
|
|
|
|
Subprocess using transport and protocol
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
Example of a subprocess protocol using to get the output of a subprocess and to
|
|
wait for the subprocess exit. The subprocess is created by the
|
|
:meth:`BaseEventLoop.subprocess_exec` method::
|
|
|
|
import asyncio
|
|
import sys
|
|
|
|
class DateProtocol(asyncio.SubprocessProtocol):
|
|
def __init__(self, exit_future):
|
|
self.exit_future = exit_future
|
|
self.output = bytearray()
|
|
|
|
def pipe_data_received(self, fd, data):
|
|
self.output.extend(data)
|
|
|
|
def process_exited(self):
|
|
self.exit_future.set_result(True)
|
|
|
|
@asyncio.coroutine
|
|
def get_date(loop):
|
|
code = 'import datetime; print(datetime.datetime.now())'
|
|
exit_future = asyncio.Future(loop=loop)
|
|
|
|
# Create the subprocess controlled by the protocol DateProtocol,
|
|
# redirect the standard output into a pipe
|
|
create = loop.subprocess_exec(lambda: DateProtocol(exit_future),
|
|
sys.executable, '-c', code,
|
|
stdin=None, stderr=None)
|
|
transport, protocol = yield from create
|
|
|
|
# Wait for the subprocess exit using the process_exited() method
|
|
# of the protocol
|
|
yield from exit_future
|
|
|
|
# Close the stdout pipe
|
|
transport.close()
|
|
|
|
# Read the output which was collected by the pipe_data_received()
|
|
# method of the protocol
|
|
data = bytes(protocol.output)
|
|
return data.decode('ascii').rstrip()
|
|
|
|
if sys.platform == "win32":
|
|
loop = asyncio.ProactorEventLoop()
|
|
asyncio.set_event_loop(loop)
|
|
else:
|
|
loop = asyncio.get_event_loop()
|
|
|
|
date = loop.run_until_complete(get_date(loop))
|
|
print("Current date: %s" % date)
|
|
loop.close()
|
|
|
|
|
|
Subprocess using streams
|
|
^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
Example using the :class:`~asyncio.subprocess.Process` class to control the
|
|
subprocess and the :class:`StreamReader` class to read from the standard
|
|
output. The subprocess is created by the :func:`create_subprocess_exec`
|
|
function::
|
|
|
|
import asyncio.subprocess
|
|
import sys
|
|
|
|
@asyncio.coroutine
|
|
def get_date():
|
|
code = 'import datetime; print(datetime.datetime.now())'
|
|
|
|
# Create the subprocess, redirect the standard output into a pipe
|
|
create = asyncio.create_subprocess_exec(sys.executable, '-c', code,
|
|
stdout=asyncio.subprocess.PIPE)
|
|
proc = yield from create
|
|
|
|
# Read one line of output
|
|
data = yield from proc.stdout.readline()
|
|
line = data.decode('ascii').rstrip()
|
|
|
|
# Wait for the subprocess exit
|
|
yield from proc.wait()
|
|
return line
|
|
|
|
if sys.platform == "win32":
|
|
loop = asyncio.ProactorEventLoop()
|
|
asyncio.set_event_loop(loop)
|
|
else:
|
|
loop = asyncio.get_event_loop()
|
|
|
|
date = loop.run_until_complete(get_date())
|
|
print("Current date: %s" % date)
|
|
loop.close()
|