Messages in this thread | | | Date | Tue, 28 Apr 1998 22:32:32 -0700 (PDT) | From | Dean Gaudet <> | Subject | OFFTOPIC: write atomicity |
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This topic came up recently while I was playing with porting Apache to NSPR (netscape's portable runtime): "What guarantees are there on the atomicity of writes?"
Single Unix has a satisfying answer for pipes, FIFOs, and STREAMS. But it doesn't really give an answer for regular files, or for network sockets.
I know from experience, that for plain files there is an atomicity guarantee on every unix out there... otherwise Apache's log files, for example, would be completely broken because there are several processes writing them all the time, and in the past four years nobody has complained of jumbled log messages. But Single Unix doesn't mention this, or give a lower bound for the atomicity.
I generally use the heuristic that if it's <= PIPE_BUF bytes in size I'm probably safe everywhere... but I wouldn't mind having a standard to point at.
Two questions:
Is there a standard which guarantees this for files and sockets?
What are linux's guarantees?
Dean
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