From cddfac92a62198161f6265c8035617b65fb1a623 Mon Sep 17 00:00:00 2001 From: Brett Cannon Date: Wed, 9 Sep 2009 16:17:44 +0000 Subject: [PATCH] Remove backticks from a plaintext PEP. --- pep-3145.txt | 54 ++++++++++++++++++++++------------------------------ 1 file changed, 23 insertions(+), 31 deletions(-) diff --git a/pep-3145.txt b/pep-3145.txt index 3c8dcf7e6..9e1d6733f 100644 --- a/pep-3145.txt +++ b/pep-3145.txt @@ -12,10 +12,10 @@ Post-History: Abstract: - In its present form, the ``subprocess.Popen`` implementation is prone to + In its present form, the subprocess.Popen implementation is prone to dead-locking and blocking of the parent Python script while waiting on data from the child process. This PEP proposes to make - ``subprocess.Popen`` more asynchronous to help alleviate these + subprocess.Popen more asynchronous to help alleviate these problems. Motivation: @@ -26,7 +26,7 @@ Motivation: blocking to wait for the program to produce data [1] [2] [3]. The current behavior of the subprocess module is that when a user sends or receives data via the stdin, stderr and stdout file objects, dead locks are common - and documented [4] [5]. While ``communicate`` can be used to alleviate some of + and documented [4] [5]. While communicate can be used to alleviate some of the buffering issues, it will still cause the parent process to block while attempting to read data when none is available to be read from the child process. @@ -34,14 +34,13 @@ Motivation: Rationale: There is a documented need for asynchronous, non-blocking functionality in - ``subprocess.Popen`` [6] [7] [2] [3]. Inclusion of the code would improve the + subprocess.Popen [6] [7] [2] [3]. Inclusion of the code would improve the utility of the Python standard library that can be used on Unix based and Windows builds of Python. Practically every I/O object in Python has a file-like wrapper of some sort. Sockets already act as such and for - strings there is ``StringIO``. Popen can be made to act like a file by simply - using the methods attached the the ``subprocess.Popen.stderr``, - ``stdout`` and - ``stdin`` file-like objects. But when using the read and write methods of + strings there is StringIO. Popen can be made to act like a file by simply + using the methods attached the the subprocess.Popen.stderr, stdout and + stdin file-like objects. But when using the read and write methods of those options, you do not have the benefit of asynchronous I/O. In the proposed solution the wrapper wraps the asynchronous methods to mimic a file object. @@ -53,43 +52,36 @@ Reference Implementation: the problems I have come across in the development process [10]. I have been working on implementing non-blocking asynchronous I/O in the - ``subprocess.Popen`` module as well as a wrapper class for - ``subprocess.Popen`` + subprocess.Popen module as well as a wrapper class for subprocess.Popen that makes it so that an executed process can take the place of a file by duplicating all of the methods and attributes that file objects have. - There are two base functions that have been added to the - ``subprocess.Popen`` - class: ``Popen.send`` and ``Popen._recv``, each with two separate implementations, + There are two base functions that have been added to the subprocess.Popen + class: Popen.send and Popen._recv, each with two separate implementations, one for Windows and one for Unix based systems. The Windows - implementation uses ``ctypes`` to access the functions needed to control pipes + implementation uses ctypes to access the functions needed to control pipes in the kernel 32 DLL in an asynchronous manner. On Unix based systems, the Python interface for file control serves the same purpose. The - different implementations of ``Popen.send`` and ``Popen._recv`` have identical + different implementations of Popen.send and Popen._recv have identical arguments to make code that uses these functions work across multiple platforms. - When calling the ``Popen._recv`` function, it requires the pipe name be - passed as an argument so there exists the ``Popen.recv`` function that passes - selects ``stdout`` as the pipe for ``Popen._recv`` by default. - ``Popen.recv_err`` - selects ``stderr`` as the pipe by default. ``Popen.recv`` and - ``Popen.recv_err`` - are much easier to read and understand than - ``Popen._recv('stdout' ...)`` and - ``Popen._recv('stderr' ...)`` respectively. + When calling the Popen._recv function, it requires the pipe name be + passed as an argument so there exists the Popen.recv function that passes + selects stdout as the pipe for Popen._recv by default. Popen.recv_err + selects stderr as the pipe by default. Popen.recv and Popen.recv_err + are much easier to read and understand than Popen._recv('stdout' ...) and + Popen._recv('stderr' ...) respectively. - Since the ``Popen._recv`` function does not wait on data to be produced - before returning a value, it may return empty bytes. - ``Popen.asyncread`` + Since the Popen._recv function does not wait on data to be produced + before returning a value, it may return empty bytes. Popen.asyncread handles this issue by returning all data read over a given time interval. - The ``ProcessIOWrapper`` class uses the ``asyncread`` and - ``asyncwrite`` functions to + The ProcessIOWrapper class uses the asyncread and asyncwrite functions to allow a process to act like a file so that there are no blocking issues - that can arise from using the ``stdout`` and ``stdin`` file objects produced from - a ``subprocess.Popen`` call. + that can arise from using the stdout and stdin file objects produced from + a subprocess.Popen call. References: