Bob Friesenhahn wrote: >> Can any of you think of other subsets of mmap functionality that are >> worth supplying a test for in autoconf? Do any of you have time to >> work on patches for any or all of this? > > GraphicsMagick has a GM_FUNC_MMAP_FILEIO macro which does this: > > This test is derived from GNU Autoconf's similar macro. > The purpose of this test is to verify that files may be memory > mapped, and that memory mapping and file I/O are coherent. > > The test creates a test file, memory maps the file, updates > the file using the memory map, and then reads the file using > file I/O to verify that the file contains the updates. > > This functionality would be useful in Autoconf if variants are accepted.
With the notable exception of OpenBSD, all modern OSs from the past 20+ years have unified buffer caches, so coherence is implicitly maintained between mmap and read/write. Of course on Windows it's possible to intentionally break coherence by doing an unbuffered write, which would make any cached copy of a page stale. -- -- Howard Chu CTO, Symas Corp. http://www.symas.com Director, Highland Sun http://highlandsun.com/hyc/ Chief Architect, OpenLDAP http://www.openldap.org/project/
