Remove backticks from a plaintext PEP.
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pep-3145.txt
54
pep-3145.txt
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@ -12,10 +12,10 @@ Post-History:
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Abstract:
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In its present form, the ``subprocess.Popen`` implementation is prone to
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In its present form, the subprocess.Popen implementation is prone to
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dead-locking and blocking of the parent Python script while waiting on data
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from the child process. This PEP proposes to make
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``subprocess.Popen`` more asynchronous to help alleviate these
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subprocess.Popen more asynchronous to help alleviate these
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problems.
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Motivation:
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@ -26,7 +26,7 @@ Motivation:
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blocking to wait for the program to produce data [1] [2] [3]. The current
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behavior of the subprocess module is that when a user sends or receives
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data via the stdin, stderr and stdout file objects, dead locks are common
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and documented [4] [5]. While ``communicate`` can be used to alleviate some of
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and documented [4] [5]. While communicate can be used to alleviate some of
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the buffering issues, it will still cause the parent process to block while
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attempting to read data when none is available to be read from the child
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process.
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@ -34,14 +34,13 @@ Motivation:
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Rationale:
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There is a documented need for asynchronous, non-blocking functionality in
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``subprocess.Popen`` [6] [7] [2] [3]. Inclusion of the code would improve the
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subprocess.Popen [6] [7] [2] [3]. Inclusion of the code would improve the
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utility of the Python standard library that can be used on Unix based and
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Windows builds of Python. Practically every I/O object in Python has a
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file-like wrapper of some sort. Sockets already act as such and for
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strings there is ``StringIO``. Popen can be made to act like a file by simply
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using the methods attached the the ``subprocess.Popen.stderr``,
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``stdout`` and
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``stdin`` file-like objects. But when using the read and write methods of
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strings there is StringIO. Popen can be made to act like a file by simply
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using the methods attached the the subprocess.Popen.stderr, stdout and
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stdin file-like objects. But when using the read and write methods of
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those options, you do not have the benefit of asynchronous I/O. In the
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proposed solution the wrapper wraps the asynchronous methods to mimic a
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file object.
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@ -53,43 +52,36 @@ Reference Implementation:
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the problems I have come across in the development process [10].
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I have been working on implementing non-blocking asynchronous I/O in the
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``subprocess.Popen`` module as well as a wrapper class for
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``subprocess.Popen``
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subprocess.Popen module as well as a wrapper class for subprocess.Popen
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that makes it so that an executed process can take the place of a file by
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duplicating all of the methods and attributes that file objects have.
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There are two base functions that have been added to the
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``subprocess.Popen``
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class: ``Popen.send`` and ``Popen._recv``, each with two separate implementations,
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There are two base functions that have been added to the subprocess.Popen
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class: Popen.send and Popen._recv, each with two separate implementations,
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one for Windows and one for Unix based systems. The Windows
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implementation uses ``ctypes`` to access the functions needed to control pipes
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implementation uses ctypes to access the functions needed to control pipes
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in the kernel 32 DLL in an asynchronous manner. On Unix based systems,
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the Python interface for file control serves the same purpose. The
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different implementations of ``Popen.send`` and ``Popen._recv`` have identical
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different implementations of Popen.send and Popen._recv have identical
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arguments to make code that uses these functions work across multiple
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platforms.
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When calling the ``Popen._recv`` function, it requires the pipe name be
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passed as an argument so there exists the ``Popen.recv`` function that passes
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selects ``stdout`` as the pipe for ``Popen._recv`` by default.
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``Popen.recv_err``
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selects ``stderr`` as the pipe by default. ``Popen.recv`` and
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``Popen.recv_err``
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are much easier to read and understand than
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``Popen._recv('stdout' ...)`` and
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``Popen._recv('stderr' ...)`` respectively.
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When calling the Popen._recv function, it requires the pipe name be
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passed as an argument so there exists the Popen.recv function that passes
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selects stdout as the pipe for Popen._recv by default. Popen.recv_err
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selects stderr as the pipe by default. Popen.recv and Popen.recv_err
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are much easier to read and understand than Popen._recv('stdout' ...) and
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Popen._recv('stderr' ...) respectively.
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Since the ``Popen._recv`` function does not wait on data to be produced
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before returning a value, it may return empty bytes.
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``Popen.asyncread``
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Since the Popen._recv function does not wait on data to be produced
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before returning a value, it may return empty bytes. Popen.asyncread
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handles this issue by returning all data read over a given time
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interval.
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The ``ProcessIOWrapper`` class uses the ``asyncread`` and
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``asyncwrite`` functions to
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The ProcessIOWrapper class uses the asyncread and asyncwrite functions to
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allow a process to act like a file so that there are no blocking issues
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that can arise from using the ``stdout`` and ``stdin`` file objects produced from
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a ``subprocess.Popen`` call.
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that can arise from using the stdout and stdin file objects produced from
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a subprocess.Popen call.
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References:
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