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CVS patch #477161: New "access" keyword for mmap, from Jay T Miller.

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This gives mmap() on Windows the ability to create read-only, write-
through and copy-on-write mmaps.  A new keyword argument is introduced
because the mmap() signatures diverged between Windows and Unix, so
while they (now) both support this functionality, there wasn't a way to
spell it in a common way without introducing a new spelling gimmick.
The old spellings are still accepted, so there isn't a backward-
compatibility issue here.
This commit is contained in:
Tim Peters 2001-11-13 23:11:19 +00:00
parent afeb2a4d89
commit 5ebfd36afa
5 changed files with 411 additions and 144 deletions
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162
Doc/lib/libmmap.tex
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@ -1,5 +1,5 @@
\section{\module{mmap} ---
Memory-mapped file support}
Memory-mapped file support}
\declaremodule{builtin}{mmap}
\modulesynopsis{Interface to memory-mapped files for Unix and Windows.}
@ -23,36 +23,67 @@ If you wish to map an existing Python file object, use its
\function{os.open()} function, which returns a file descriptor
directly (the file still needs to be closed when done).
\begin{funcdesc}{mmap}{fileno, length\optional{, tagname}}
\strong{(Windows version)} Maps \var{length} bytes from the file
specified by the file handle \var{fileno}, and returns a mmap object.
If \var{length} is \code{0}, the maximum length of the map will be the
current size of the file when \function{mmap()} is called.
\var{tagname}, if specified and not \code{None}, is a string giving a
tag name for the mapping. Windows allows you to have many different
mappings against the same file. If you specify the name of an
existing tag, that tag is opened, otherwise a new tag of this name is
created. If this parameter is omitted or \code{None}, the mapping is
created without a name. Avoiding the use of the tag parameter will
assist in keeping your code portable between \UNIX{} and Windows.
\begin{funcdesc}{mmap}{fileno, length\optional{, tagname\optional{, access}}}
\strong{(Windows version)} Maps \var{length} bytes from the file
specified by the file handle \var{fileno}, and returns a mmap
object. If \var{length} is \code{0}, the maximum length of the map
will be the current size of the file when \function{mmap()} is
called.
\var{tagname}, if specified and not \code{None}, is a string giving
a tag name for the mapping. Windows allows you to have many
different mappings against the same file. If you specify the name
of an existing tag, that tag is opened, otherwise a new tag of this
name is created. If this parameter is omitted or \code{None}, the
mapping is created without a name. Avoiding the use of the tag
parameter will assist in keeping your code portable between \UNIX{}
and Windows.
\var{access} may be specified as an optional keyword parameter.
\var{access} accepts one of three values: \constant{ACCESS_READ},
\constant{ACCESS_WRITE}, or \constant{ACCESS_COPY} to specify
readonly, write-through or copy-on-write memory respectively.
\var{access} can be used on both \UNIX{} and Windows. If
\var{access} is not specified, Windows mmap returns a write-through
mapping. The initial memory values for all three access types are
taken from the specified file. Assignment to an
\constant{ACCESS_READ} memory map raises a \exception{TypeError}
exception. Assignment to an \constant{ACCESS_WRITE} memory map
affects both memory and the underlying file. Assigment to an
\constant{ACCESS_COPY} memory map affects memory but does not update
the underlying file.
\end{funcdesc}
\begin{funcdesc}{mmap}{fileno, length\optional{, flags\optional{, prot}}}
\strong{(\UNIX{} version)} Maps \var{length} bytes from the file
specified by the file descriptor \var{fileno}, and returns a mmap object.
\var{flags} specifies the nature of the mapping.
\constant{MAP_PRIVATE} creates a private copy-on-write mapping, so
changes to the contents of the mmap object will be private to this
process, and \constant{MAP_SHARED} creates a mapping that's shared
with all other processes mapping the same areas of the file.
The default value is \constant{MAP_SHARED}.
\var{prot}, if specified, gives the desired memory protection; the two
most useful values are \constant{PROT_READ} and \constant{PROT_WRITE},
to specify that the pages may be read or written.
\var{prot} defaults to \constant{PROT_READ | PROT_WRITE}.
\begin{funcdesc}{mmap}{fileno, length\optional{, flags\optional{, prot\optional{, access}}}}
\strong{(\UNIX{} version)} Maps \var{length} bytes from the file
specified by the file descriptor \var{fileno}, and returns a mmap
object.
\var{flags} specifies the nature of the mapping.
\constant{MAP_PRIVATE} creates a private copy-on-write mapping, so
changes to the contents of the mmap object will be private to this
process, and \constant{MAP_SHARED} creates a mapping that's shared
with all other processes mapping the same areas of the file. The
default value is \constant{MAP_SHARED}.
\var{prot}, if specified, gives the desired memory protection; the
two most useful values are \constant{PROT_READ} and
\constant{PROT_WRITE}, to specify that the pages may be read or
written. \var{prot} defaults to \constant{PROT_READ | PROT_WRITE}.
\var{access} may be specified in lieu of \var{flags} and \var{prot}
as an optional keyword parameter. \var{access} accepts one of three
values: \constant{ACCESS_READ}, \constant{ACCESS_WRITE}, or
\constant{ACCESS_COPY} to specify readonly, write-through, or
copy-on-write memory respectively. \var{access} can be used on both
\UNIX{} and Windows. It is an error to specify both \var{flags},
\var{prot} and \var{access}. The initial memory values for all
three access types are taken from the specified file. Assignment to
an \constant{ACCESS_READ} memory map raises a \exception{TypeError}
exception. Assignment to an \constant{ACCESS_WRITE} memory map
affects both memory and the underlying file. Assigment to an
\constant{ACCESS_COPY} memory map affects memory but does not update
the underlying file.
\end{funcdesc}
@ -60,73 +91,80 @@ Memory-mapped file objects support the following methods:
\begin{methoddesc}{close}{}
Close the file. Subsequent calls to other methods of the object
will result in an exception being raised.
Close the file. Subsequent calls to other methods of the object
will result in an exception being raised.
\end{methoddesc}
\begin{methoddesc}{find}{string\optional{, start}}
Returns the lowest index in the object where the substring
\var{string} is found. Returns \code{-1} on failure. \var{start} is
the index at which the search begins, and defaults to zero.
Returns the lowest index in the object where the substring
\var{string} is found. Returns \code{-1} on failure. \var{start}
is the index at which the search begins, and defaults to zero.
\end{methoddesc}
\begin{methoddesc}{flush}{\optional{offset, size}}
Flushes changes made to the in-memory copy of a file back to disk.
Without use of this call there is no guarantee that changes are
written back before the object is destroyed. If \var{offset} and
\var{size} are specified, only changes to the given range of bytes
will be flushed to disk; otherwise, the whole extent of the mapping is
flushed.
Flushes changes made to the in-memory copy of a file back to disk.
Without use of this call there is no guarantee that changes are
written back before the object is destroyed. If \var{offset} and
\var{size} are specified, only changes to the given range of bytes
will be flushed to disk; otherwise, the whole extent of the mapping
is flushed.
\end{methoddesc}
\begin{methoddesc}{move}{\var{dest}, \var{src}, \var{count}}
Copy the \var{count} bytes starting at offset \var{src}
to the destination index \var{dest}.
Copy the \var{count} bytes starting at offset \var{src} to the
destination index \var{dest}. If the mmap was created with
\constant{ACCESS_READ}, then calls to move will throw a
\exception{TypeError} exception.
\end{methoddesc}
\begin{methoddesc}{read}{\var{num}}
Return a string containing up to \var{num} bytes starting from the
current file position; the file position is updated to point after the
bytes that were returned.
Return a string containing up to \var{num} bytes starting from the
current file position; the file position is updated to point after the
bytes that were returned.
\end{methoddesc}
\begin{methoddesc}{read_byte}{}
Returns a string of length 1 containing the character at the current
file position, and advances the file position by 1.
Returns a string of length 1 containing the character at the current
file position, and advances the file position by 1.
\end{methoddesc}
\begin{methoddesc}{readline}{}
Returns a single line, starting at the current file position and up to
the next newline.
Returns a single line, starting at the current file position and up to
the next newline.
\end{methoddesc}
\begin{methoddesc}{resize}{\var{newsize}}
If the mmap was created with \constant{ACCESS_READ} or
\constant{ACCESS_COPY}, resizing the map will throw a \exception{TypeError} exception.
\end{methoddesc}
\begin{methoddesc}{seek}{pos\optional{, whence}}
Set the file's current position.
\var{whence} argument is optional and defaults to \code{0} (absolute
file positioning); other values are \code{1} (seek relative to the
current position) and \code{2} (seek relative to the file's end).
Set the file's current position. \var{whence} argument is optional
and defaults to \code{0} (absolute file positioning); other values
are \code{1} (seek relative to the current position) and \code{2}
(seek relative to the file's end).
\end{methoddesc}
\begin{methoddesc}{size}{}
Return the length of the file, which can be larger than the size
of the memory-mapped area.
Return the length of the file, which can be larger than the size of
the memory-mapped area.
\end{methoddesc}
\begin{methoddesc}{tell}{}
Returns the current position of the file pointer.
Returns the current position of the file pointer.
\end{methoddesc}
\begin{methoddesc}{write}{\var{string}}
Write the bytes in \var{string} into memory at the current position of
the file pointer; the file position is updated to point after the
bytes that were written.
Write the bytes in \var{string} into memory at the current position
of the file pointer; the file position is updated to point after the
bytes that were written. If the mmap was created with
\constant{ACCESS_READ}, then writing to it will throw a
\exception{TypeError} exception.
\end{methoddesc}
\begin{methoddesc}{write_byte}{\var{byte}}
Write the single-character string \var{byte} into memory at the
current position of the file pointer; the file position is advanced by
\code{1}.
Write the single-character string \var{byte} into memory at the
current position of the file pointer; the file position is advanced
by \code{1}.If the mmap was created with \constant{ACCESS_READ},
then writing to it will throw a \exception{TypeError} exception.
\end{methoddesc}