Hal Murray <hmur...@megapathdsl.net>: > I'm not enough of a Unix file system wizard. Are there any guarantees about > multi-threaded writes to the same file not getting scrambled? Will it work > if > we buffer everything into a big buffer and do a single write?
Under Linux, yes, up to 4096 bytes. Look for "I wrote a script to test" on this page: https://stackoverflow.com/questions/1154446/is-file-append-atomic-in-unix There's a great deal of confusion abroad about this. The first answer reflects a widespread belief that 512-byte writes are guaranteed atomic by POSIX. That belief is wrong, as is pointed out in the comments. PIPE_BUF is a real thing in POSIX but has nothing to do with file writes. I am here to add that I believe the myth about POSIX persists in practice because 512 byte file write(2) operations *are* in fact atomic on every Unix. So the mythology about PIPE_BUF is only half wrong; POSIX does not require it but it's true anyway. Yes, I have used this assumption in production code under multiple Unixes and not been bitten. The way I would recommend handling this is with a PIPE_BUF sized buffer, write(2), and a comment that explains that PIPE_BUF is accidentally correct here. Been there, done that myself. This is very old lore. -- <a href="http://www.catb.org/~esr/";>Eric S. Raymond</a> My work is funded by the Internet Civil Engineering Institute: https://icei.org Please visit their site and donate: the civilization you save might be your own. _______________________________________________ devel mailing list devel@ntpsec.org http://lists.ntpsec.org/mailman/listinfo/devel
