Hello Duncan, Friday, January 27, 2006, 4:00:28 PM, you wrote:
moreover, i have an idea how to implement async i/o without complex burecreacy: use mmapped files, may be together with miltiple buffers. for example, we can allocate four 16kb buffers. when one buffer is filled with written data, the program unmaps it and switches to use the next buffer. i don't tested it, but OS can guess that unmapped buffer now should be asynchronously written to disk. the same for reading - when we completely read one buffer, we can unmap it, switch to the second buffer and map the third so that the OS can asynchronously fill the third buffer while we are reading second. should this work, at least on the main desktop OSes?
DC> On Linux an probably other unix-like OSes I don't think this would be DC> any different from using read/write. DC> On Linux, read and mmap use the same underlying mechanism - the page DC> cache. The only difference is that with mmap you get zero-copy access to DC> the page cache. However frequent mapping and unmapping may eliminate DC> that advantage. Either way there is no difference in how asynchronous DC> the operations are. yes, i want to save exactly this bit of performance - after i optimized all other expenses on the path of text i/o in other words, i interested in having zero-wait operation both for reading and writing, i.e. that in sequence of getChar or putChar actions there were no waits on any action - of course, if the disk is fast enough. in other words, speed of such i/o programs should be the same as if we just write these data to memory current GHC's Handle implementation uses rather complex machinery for async reading and writing, and i can even say that most part of Handle's implementation complexity is due to this async machinery. so i wanna know what exactly accomplished by this implementation and can we implement async operation much easier by using mmap? the word "async" is overloaded here - i'm most interested in having zero-overhead in single-threaded operation, while GHC's optimization, afair, is more about overlapping I/O in one thread with computations in another. so i'm searching for fastest and easiest-to-implement scheme. what you propose? -- Best regards, Bulat mailto:bulatz@HotPOP.com