Author: Eugene Nalimov
Date: 09:32:54 03/02/01
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On March 02, 2001 at 10:03:58, Pat King wrote: >On March 02, 2001 at 08:45:51, Robert Hyatt wrote: > >>On March 02, 2001 at 08:39:57, Pat King wrote: >> >>>if sizeof(somebuiltintype) <= sizeof(sig_atomic_t), is it garunteed that reads >>>and writes of somebuiltintype are atomic? >>> >>>thanks. >>> >>>Pat >> >> >>I don't think it matters. You _first_ use an atomic operation to lock the >>data in question, then you don't have to worry about whether the read/write >>is atomic. IE my hash entries are 16 bytes so that would probably never be >>an atomic read/write. > >But if the data in question is very simple (as in this case setting a bool flag >or two) then a lock seems overkill. certainly almost any struct wouldn't be, but >what of a bool or a char? For instance, my compiler (mingw) has sig_atomic_t as >a typedef int, 4 bytes. so is anything 4 bytes or smaller atomic? On x86, no. Your data can be unaligned (absolutely valid on any x86 OS I know of), cross the page boundary, and one of the pages can be swapped out. Then you'll get the OS call in the middle of the memory write. Eugene
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