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Aucbvax.4878 fa.unix-wizards utzoo!decvax!ucbvax!unix-wizards Sun Nov 1 16:20:54 1981 shared data >From dsp.dove@MIT-SPEECH@MIT-AI Sun Nov 1 16:09:46 1981 I don't see why a dispatch vector would be worth it. The loader would have to be hacked to provide info about sharing anyway. Also several kernel mods would have to be made to map apr's.

The main problem I used to have is that all progs had the shared data in the same virtual address (the code wasn't pic). This meant that if several shared segments were contemplated one could be in the bind of choosing which to use. Also, because the address binding was done so early, any change to the shared library required the users to recompile everything. A vax would eliminate the virtual address contention problem probably, but getting unix to make pic would be hard I expect.

By shared data, I meant a scheme whereby a file represented a shared data area (as it does for text) and users could perform a sys call to allocate some aprs to map a portion of it. A given segment of the file would be locked in memory (perhaps the whole thing, but that would limit its usefulness) as long as any proc had it referenced, and that would be done in a similar way to text locking. Finally, unlike text, when the data was swapped out, it would have to be written to the file.

All this would in addition require some semaphore mechanism to permit controlled access, but that part would be fairly simple.

This means of interprocess communication would be mainly for handling enourmous common database problems that want to be fast, and to allow things like array processing on 11's (provided the entire data file need not be resident).

Myron Zimmerman should be credited with this idea (unless someone has already done it). -------

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