Paul Rubin <no.email@nospam.invalid>: > I'd be interested to know how to open a disk file asynchronously in a > single-threaded Python program under Linux. As far as I can tell there > is no way to do it.
Traditionally, disk access in Linux has been considered nonblocking. There is AIO, but that hasn't been used much. I have seen quite a bit of activity on the Linux FS mailing list recently on AIO so maybe that will change in the future. I believe the lack of asynchronous disk I/O is related to the grand Solaris idea which Linux adopted: all memory is on a disk and RAM is merely a cache. You can turn disk access into memory access with mmap() and you can turn memory access into disk access with /proc/mem. If you access a file and the relevant bytes are already cached in RAM you get them instantaneously; otherwise you'll have to wait for a "page fault" to be processed. If you need to execute a CPU instruction and the relevant address is already cached in RAM, the CPU can proceed without delay; otherwise the CPU will have to wait for a page fault to be processed. As swapping is no longer considered normal on modern computers, the memory-disk duality doesn't seem all that practical anymore. Rather, you'd like to treat the disk analogously to network access and keep RAM access separate. Marko -- https://mail.python.org/mailman/listinfo/python-list
