Paul Rubin <http://[EMAIL PROTECTED]> writes:
> "sturlamolden" <[EMAIL PROTECTED]> writes: >> However, "memory mapping" a file by means of fseek() is probably more >> efficient than using UNIX' mmap() or Windows' >> CreateFileMapping()/MapViewOfFile(). > > Why on would you think that?! It is counterintuitive. fseek beyond > whatever is buffered in stdio (usually no more than 1kbyte or so) > requires a system call, while mmap is just a memory access. And the buffer copy required with every I/O from/to the application. >> In Python, we don't always need the file memory mapped, we normally >> just want to use slicing-operators, for-loops and other goodies on >> the file object -- i.e. we just want to treat the file as a Python >> container object. There are many ways of achieving that. > > Some of the time we want to share the region with other processes. > Sometimes we just want random access to a big file on disk without > having to do a lot of context switches seeking around in the file. > >> There are in any case room for improving Python's mmap object. > > IMO it should have some kind of IPC locking mechanism added, in > addition to the offset stuff suggested. The type of IPC required differs depending on who is using the shared region - either another python process or another external program. Apart from the spinlock primitives, other types of synchronization mechanisms are provided by the OS. However, I do see value in providing a shared memory based spinlock mechanism. These services can be built on top of the shared memory infrastructure. I am not sure what kind or real world python applications use it. -Chetan -- http://mail.python.org/mailman/listinfo/python-list
