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532 lines
18 KiB
Python
532 lines
18 KiB
Python
"""Provides shared memory for direct access across processes.
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The API of this package is currently provisional. Refer to the
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documentation for details.
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"""
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__all__ = [ 'SharedMemory', 'ShareableList' ]
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from functools import partial
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import mmap
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import os
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import errno
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import struct
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import secrets
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import types
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if os.name == "nt":
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import _winapi
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_USE_POSIX = False
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else:
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import _posixshmem
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_USE_POSIX = True
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_O_CREX = os.O_CREAT | os.O_EXCL
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# FreeBSD (and perhaps other BSDs) limit names to 14 characters.
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_SHM_SAFE_NAME_LENGTH = 14
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# Shared memory block name prefix
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if _USE_POSIX:
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_SHM_NAME_PREFIX = '/psm_'
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else:
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_SHM_NAME_PREFIX = 'wnsm_'
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def _make_filename():
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"Create a random filename for the shared memory object."
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# number of random bytes to use for name
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nbytes = (_SHM_SAFE_NAME_LENGTH - len(_SHM_NAME_PREFIX)) // 2
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assert nbytes >= 2, '_SHM_NAME_PREFIX too long'
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name = _SHM_NAME_PREFIX + secrets.token_hex(nbytes)
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assert len(name) <= _SHM_SAFE_NAME_LENGTH
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return name
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class SharedMemory:
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"""Creates a new shared memory block or attaches to an existing
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shared memory block.
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Every shared memory block is assigned a unique name. This enables
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one process to create a shared memory block with a particular name
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so that a different process can attach to that same shared memory
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block using that same name.
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As a resource for sharing data across processes, shared memory blocks
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may outlive the original process that created them. When one process
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no longer needs access to a shared memory block that might still be
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needed by other processes, the close() method should be called.
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When a shared memory block is no longer needed by any process, the
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unlink() method should be called to ensure proper cleanup."""
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# Defaults; enables close() and unlink() to run without errors.
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_name = None
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_fd = -1
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_mmap = None
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_buf = None
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_flags = os.O_RDWR
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_mode = 0o600
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_prepend_leading_slash = True if _USE_POSIX else False
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def __init__(self, name=None, create=False, size=0):
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if not size >= 0:
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raise ValueError("'size' must be a positive integer")
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if create:
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self._flags = _O_CREX | os.O_RDWR
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if size == 0:
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raise ValueError("'size' must be a positive number different from zero")
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if name is None and not self._flags & os.O_EXCL:
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raise ValueError("'name' can only be None if create=True")
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if _USE_POSIX:
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# POSIX Shared Memory
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if name is None:
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while True:
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name = _make_filename()
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try:
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self._fd = _posixshmem.shm_open(
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name,
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self._flags,
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mode=self._mode
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)
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except FileExistsError:
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continue
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self._name = name
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break
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else:
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name = "/" + name if self._prepend_leading_slash else name
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self._fd = _posixshmem.shm_open(
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name,
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self._flags,
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mode=self._mode
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)
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self._name = name
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try:
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if create and size:
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os.ftruncate(self._fd, size)
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stats = os.fstat(self._fd)
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size = stats.st_size
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self._mmap = mmap.mmap(self._fd, size)
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except OSError:
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self.unlink()
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raise
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from .resource_tracker import register
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register(self._name, "shared_memory")
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else:
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# Windows Named Shared Memory
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if create:
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while True:
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temp_name = _make_filename() if name is None else name
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# Create and reserve shared memory block with this name
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# until it can be attached to by mmap.
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h_map = _winapi.CreateFileMapping(
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_winapi.INVALID_HANDLE_VALUE,
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_winapi.NULL,
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_winapi.PAGE_READWRITE,
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(size >> 32) & 0xFFFFFFFF,
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size & 0xFFFFFFFF,
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temp_name
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)
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try:
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last_error_code = _winapi.GetLastError()
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if last_error_code == _winapi.ERROR_ALREADY_EXISTS:
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if name is not None:
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raise FileExistsError(
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errno.EEXIST,
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os.strerror(errno.EEXIST),
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name,
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_winapi.ERROR_ALREADY_EXISTS
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)
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else:
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continue
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self._mmap = mmap.mmap(-1, size, tagname=temp_name)
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finally:
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_winapi.CloseHandle(h_map)
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self._name = temp_name
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break
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else:
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self._name = name
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# Dynamically determine the existing named shared memory
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# block's size which is likely a multiple of mmap.PAGESIZE.
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h_map = _winapi.OpenFileMapping(
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_winapi.FILE_MAP_READ,
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False,
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name
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)
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try:
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p_buf = _winapi.MapViewOfFile(
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h_map,
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_winapi.FILE_MAP_READ,
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0,
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0,
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0
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)
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finally:
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_winapi.CloseHandle(h_map)
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size = _winapi.VirtualQuerySize(p_buf)
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self._mmap = mmap.mmap(-1, size, tagname=name)
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self._size = size
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self._buf = memoryview(self._mmap)
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def __del__(self):
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try:
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self.close()
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except OSError:
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pass
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def __reduce__(self):
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return (
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self.__class__,
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(
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self.name,
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False,
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self.size,
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),
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)
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def __repr__(self):
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return f'{self.__class__.__name__}({self.name!r}, size={self.size})'
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@property
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def buf(self):
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"A memoryview of contents of the shared memory block."
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return self._buf
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@property
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def name(self):
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"Unique name that identifies the shared memory block."
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reported_name = self._name
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if _USE_POSIX and self._prepend_leading_slash:
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if self._name.startswith("/"):
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reported_name = self._name[1:]
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return reported_name
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@property
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def size(self):
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"Size in bytes."
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return self._size
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def close(self):
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"""Closes access to the shared memory from this instance but does
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not destroy the shared memory block."""
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if self._buf is not None:
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self._buf.release()
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self._buf = None
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if self._mmap is not None:
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self._mmap.close()
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self._mmap = None
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if _USE_POSIX and self._fd >= 0:
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os.close(self._fd)
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self._fd = -1
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def unlink(self):
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"""Requests that the underlying shared memory block be destroyed.
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In order to ensure proper cleanup of resources, unlink should be
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called once (and only once) across all processes which have access
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to the shared memory block."""
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if _USE_POSIX and self._name:
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from .resource_tracker import unregister
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_posixshmem.shm_unlink(self._name)
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unregister(self._name, "shared_memory")
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_encoding = "utf8"
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class ShareableList:
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"""Pattern for a mutable list-like object shareable via a shared
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memory block. It differs from the built-in list type in that these
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lists can not change their overall length (i.e. no append, insert,
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etc.)
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Because values are packed into a memoryview as bytes, the struct
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packing format for any storable value must require no more than 8
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characters to describe its format."""
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# The shared memory area is organized as follows:
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# - 8 bytes: number of items (N) as a 64-bit integer
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# - (N + 1) * 8 bytes: offsets of each element from the start of the
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# data area
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# - K bytes: the data area storing item values (with encoding and size
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# depending on their respective types)
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# - N * 8 bytes: `struct` format string for each element
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# - N bytes: index into _back_transforms_mapping for each element
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# (for reconstructing the corresponding Python value)
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_types_mapping = {
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int: "q",
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float: "d",
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bool: "xxxxxxx?",
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str: "%ds",
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bytes: "%ds",
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None.__class__: "xxxxxx?x",
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}
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_alignment = 8
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_back_transforms_mapping = {
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0: lambda value: value, # int, float, bool
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1: lambda value: value.rstrip(b'\x00').decode(_encoding), # str
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2: lambda value: value.rstrip(b'\x00'), # bytes
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3: lambda _value: None, # None
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}
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@staticmethod
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def _extract_recreation_code(value):
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"""Used in concert with _back_transforms_mapping to convert values
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into the appropriate Python objects when retrieving them from
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the list as well as when storing them."""
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if not isinstance(value, (str, bytes, None.__class__)):
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return 0
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elif isinstance(value, str):
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return 1
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elif isinstance(value, bytes):
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return 2
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else:
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return 3 # NoneType
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def __init__(self, sequence=None, *, name=None):
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if name is None or sequence is not None:
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sequence = sequence or ()
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_formats = [
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self._types_mapping[type(item)]
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if not isinstance(item, (str, bytes))
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else self._types_mapping[type(item)] % (
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self._alignment * (len(item) // self._alignment + 1),
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)
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for item in sequence
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]
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self._list_len = len(_formats)
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assert sum(len(fmt) <= 8 for fmt in _formats) == self._list_len
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offset = 0
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# The offsets of each list element into the shared memory's
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# data area (0 meaning the start of the data area, not the start
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# of the shared memory area).
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self._allocated_offsets = [0]
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for fmt in _formats:
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offset += self._alignment if fmt[-1] != "s" else int(fmt[:-1])
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self._allocated_offsets.append(offset)
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_recreation_codes = [
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self._extract_recreation_code(item) for item in sequence
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]
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requested_size = struct.calcsize(
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"q" + self._format_size_metainfo +
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"".join(_formats) +
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self._format_packing_metainfo +
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self._format_back_transform_codes
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)
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self.shm = SharedMemory(name, create=True, size=requested_size)
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else:
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self.shm = SharedMemory(name)
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if sequence is not None:
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_enc = _encoding
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struct.pack_into(
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"q" + self._format_size_metainfo,
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self.shm.buf,
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0,
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self._list_len,
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*(self._allocated_offsets)
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)
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struct.pack_into(
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"".join(_formats),
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self.shm.buf,
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self._offset_data_start,
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*(v.encode(_enc) if isinstance(v, str) else v for v in sequence)
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)
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struct.pack_into(
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self._format_packing_metainfo,
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self.shm.buf,
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self._offset_packing_formats,
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*(v.encode(_enc) for v in _formats)
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)
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struct.pack_into(
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self._format_back_transform_codes,
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self.shm.buf,
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self._offset_back_transform_codes,
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*(_recreation_codes)
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)
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else:
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self._list_len = len(self) # Obtains size from offset 0 in buffer.
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self._allocated_offsets = list(
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struct.unpack_from(
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self._format_size_metainfo,
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self.shm.buf,
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1 * 8
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)
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)
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def _get_packing_format(self, position):
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"Gets the packing format for a single value stored in the list."
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position = position if position >= 0 else position + self._list_len
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if (position >= self._list_len) or (self._list_len < 0):
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raise IndexError("Requested position out of range.")
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v = struct.unpack_from(
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"8s",
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self.shm.buf,
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self._offset_packing_formats + position * 8
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)[0]
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fmt = v.rstrip(b'\x00')
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fmt_as_str = fmt.decode(_encoding)
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return fmt_as_str
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def _get_back_transform(self, position):
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"Gets the back transformation function for a single value."
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if (position >= self._list_len) or (self._list_len < 0):
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raise IndexError("Requested position out of range.")
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transform_code = struct.unpack_from(
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"b",
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self.shm.buf,
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self._offset_back_transform_codes + position
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)[0]
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transform_function = self._back_transforms_mapping[transform_code]
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return transform_function
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def _set_packing_format_and_transform(self, position, fmt_as_str, value):
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"""Sets the packing format and back transformation code for a
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single value in the list at the specified position."""
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if (position >= self._list_len) or (self._list_len < 0):
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raise IndexError("Requested position out of range.")
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struct.pack_into(
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"8s",
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self.shm.buf,
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self._offset_packing_formats + position * 8,
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fmt_as_str.encode(_encoding)
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)
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transform_code = self._extract_recreation_code(value)
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struct.pack_into(
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"b",
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self.shm.buf,
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self._offset_back_transform_codes + position,
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transform_code
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)
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def __getitem__(self, position):
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position = position if position >= 0 else position + self._list_len
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try:
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offset = self._offset_data_start + self._allocated_offsets[position]
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(v,) = struct.unpack_from(
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self._get_packing_format(position),
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self.shm.buf,
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offset
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)
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except IndexError:
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raise IndexError("index out of range")
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back_transform = self._get_back_transform(position)
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v = back_transform(v)
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return v
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def __setitem__(self, position, value):
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position = position if position >= 0 else position + self._list_len
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try:
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item_offset = self._allocated_offsets[position]
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offset = self._offset_data_start + item_offset
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current_format = self._get_packing_format(position)
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except IndexError:
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raise IndexError("assignment index out of range")
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if not isinstance(value, (str, bytes)):
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new_format = self._types_mapping[type(value)]
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encoded_value = value
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else:
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allocated_length = self._allocated_offsets[position + 1] - item_offset
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encoded_value = (value.encode(_encoding)
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if isinstance(value, str) else value)
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if len(encoded_value) > allocated_length:
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raise ValueError("bytes/str item exceeds available storage")
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if current_format[-1] == "s":
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new_format = current_format
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else:
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new_format = self._types_mapping[str] % (
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allocated_length,
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)
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self._set_packing_format_and_transform(
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position,
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new_format,
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value
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)
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struct.pack_into(new_format, self.shm.buf, offset, encoded_value)
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def __reduce__(self):
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return partial(self.__class__, name=self.shm.name), ()
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def __len__(self):
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return struct.unpack_from("q", self.shm.buf, 0)[0]
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def __repr__(self):
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return f'{self.__class__.__name__}({list(self)}, name={self.shm.name!r})'
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@property
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def format(self):
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"The struct packing format used by all currently stored items."
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return "".join(
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self._get_packing_format(i) for i in range(self._list_len)
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)
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@property
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def _format_size_metainfo(self):
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"The struct packing format used for the items' storage offsets."
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return "q" * (self._list_len + 1)
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@property
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def _format_packing_metainfo(self):
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"The struct packing format used for the items' packing formats."
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return "8s" * self._list_len
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@property
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def _format_back_transform_codes(self):
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"The struct packing format used for the items' back transforms."
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return "b" * self._list_len
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@property
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def _offset_data_start(self):
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# - 8 bytes for the list length
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# - (N + 1) * 8 bytes for the element offsets
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return (self._list_len + 2) * 8
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@property
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def _offset_packing_formats(self):
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return self._offset_data_start + self._allocated_offsets[-1]
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@property
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def _offset_back_transform_codes(self):
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return self._offset_packing_formats + self._list_len * 8
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def count(self, value):
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"L.count(value) -> integer -- return number of occurrences of value."
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return sum(value == entry for entry in self)
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def index(self, value):
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"""L.index(value) -> integer -- return first index of value.
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Raises ValueError if the value is not present."""
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for position, entry in enumerate(self):
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if value == entry:
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return position
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else:
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raise ValueError(f"{value!r} not in this container")
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__class_getitem__ = classmethod(types.GenericAlias)
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