使用open（）打开文件时使用的共享模式(What share mode is used when files are opened using open())

我在open()函数的参数中看不到任何内容，它允许指定文件的共享方式。因此我怀疑该文件将尽可能地被共享。特别：

打开文件进行读取时，其共享模式将允许后续打开操作打开文件进行读取，但不能写入。打开文件进行写入时，其共享模式将拒绝后续打开操作以打开文件进行读取或写入。

在我看来，这是最合乎逻辑的实施。我的假设是否正确？

更新： Martijn Pieters表示答案取决于操作系统。所以，为了这个问题，我的目标操作系统是Windows。

I can see nothing in the open() function's parameters that allows specification of how the file will be shared. I suspect therefore that the file will be shared as permissively as possible. Specifically:

When the file is opened for reading, its sharing mode will allow subsequent open operations to open the file for reading, but not for writing. When the file is opened for writing, its sharing mode will deny subsequent open operations to open the file for reading or writing.

That would seem to me to be the most logical implementation. Are my assumptions correct?

Update: Martijn Pieters states that the answer is OS dependent. So, for the sake of this question, my target OS is Windows.

最满意答案

Python在打开文件时在内部使用_wfopen() （Python 2 open()函数）或_wopen() （Python 3和io.open() ），这两者都不允许指定任何共享标志。因此，共享被设置为默认值，并且默认值不会被记录。

如果要自己设置共享模式，如果要打开指定共享模式的文件，则必须使用msvcrt.open_osfhandle() 。

Python问题跟踪器中有一个实现sharing模块的补丁，说明了如何执行此操作。只是这个补丁的开启者，有点简化，是：

import os import msvcrt import _winapi CREATE_NEW = 1 CREATE_ALWAYS = 2 OPEN_EXISTING = 3 OPEN_ALWAYS = 4 TRUNCATE_EXISTING = 5 FILE_SHARE_READ = 0x00000001 FILE_SHARE_WRITE = 0x00000002 FILE_SHARE_DELETE = 0x00000004 FILE_SHARE_VALID_FLAGS = 0x00000007 FILE_ATTRIBUTE_READONLY = 0x00000001 FILE_ATTRIBUTE_NORMAL = 0x00000080 FILE_ATTRIBUTE_TEMPORARY = 0x00000100 FILE_FLAG_DELETE_ON_CLOSE = 0x04000000 FILE_FLAG_SEQUENTIAL_SCAN = 0x08000000 FILE_FLAG_RANDOM_ACCESS = 0x10000000 GENERIC_READ = 0x80000000 GENERIC_WRITE = 0x40000000 DELETE = 0x00010000 NULL = 0 _ACCESS_MASK = os.O_RDONLY | os.O_WRONLY | os.O_RDWR _ACCESS_MAP = {os.O_RDONLY : GENERIC_READ, os.O_WRONLY : GENERIC_WRITE, os.O_RDWR : GENERIC_READ | GENERIC_WRITE} _CREATE_MASK = os.O_CREAT | os.O_EXCL | os.O_TRUNC _CREATE_MAP = {0 : OPEN_EXISTING, os.O_EXCL : OPEN_EXISTING, os.O_CREAT : OPEN_ALWAYS, os.O_CREAT | os.O_EXCL : CREATE_NEW, os.O_CREAT | os.O_TRUNC | os.O_EXCL : CREATE_NEW, os.O_TRUNC : TRUNCATE_EXISTING, os.O_TRUNC | os.O_EXCL : TRUNCATE_EXISTING, os.O_CREAT | os.O_TRUNC : CREATE_ALWAYS} def os_open(file, flags, mode=0o777, *, share_flags=FILE_SHARE_VALID_FLAGS): ''' Replacement for os.open() allowing moving or unlinking before closing ''' if not isinstance(flags, int) and mode >= 0: raise ValueError('bad flags: %r' % flags) if not isinstance(mode, int) and mode >= 0: raise ValueError('bad mode: %r' % mode) if share_flags & ~FILE_SHARE_VALID_FLAGS: raise ValueError('bad share_flags: %r' % share_flags) access_flags = _ACCESS_MAP[flags & _ACCESS_MASK] create_flags = _CREATE_MAP[flags & _CREATE_MASK] attrib_flags = FILE_ATTRIBUTE_NORMAL if flags & os.O_CREAT and mode & ~0o444 == 0: attrib_flags = FILE_ATTRIBUTE_READONLY if flags & os.O_TEMPORARY: share_flags |= FILE_SHARE_DELETE attrib_flags |= FILE_FLAG_DELETE_ON_CLOSE access_flags |= DELETE if flags & os.O_SHORT_LIVED: attrib_flags |= FILE_ATTRIBUTE_TEMPORARY if flags & os.O_SEQUENTIAL: attrib_flags |= FILE_FLAG_SEQUENTIAL_SCAN if flags & os.O_RANDOM: attrib_flags |= FILE_FLAG_RANDOM_ACCESS h = _winapi.CreateFile(file, access_flags, share_flags, NULL, create_flags, attrib_flags, NULL) return msvcrt.open_osfhandle(h, flags | os.O_NOINHERIT)

Python uses _wfopen() (Python 2 open() function) or _wopen() (Python 3 and io.open()) internally when opening files, neither of which allow for specifying any sharing flags. Sharing is thus set to a default, and what that default is does not appear to be documented.

If you want to set the sharing mode yourself, you'll have to use the msvcrt.open_osfhandle() if you want to open files specifying a sharing mode.

There is a patch in the Python issue tracker that implements a sharing module, illustrating how to do this. Just the opener from that patch, somewhat simplified, is:

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