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List:       e-lang
Subject:    Re: [e-lang] Q: what are problems with passing mutable objects
From:       Bill Frantz <frantz () pwpconsult ! com>
Date:       2002-10-21 22:05:26
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At 12:56 PM -0800 10/18/02, Mark S. Miller wrote:
>At 11:29 AM 10/18/2002 Friday, Bill Frantz wrote:
>>At 6:14 PM -0700 10/17/02, Mark S. Miller wrote:
>>>(During replay, file writes can of course
>>>go to the bit bucket.)
>>
>>If your failure model involves the computer suddenly stopping, for example
>>power failure, then you can't assume that the file write has been sent to
>>the disk.
>
>I'm confused.  How should this issue affect replay?

Sorry, I should have been more clear.

During play the program writes to block N of a file.  The OS stashes the
new value of block N in a buffer and returns to the program.  More things
happen, but the OS does not flush the buffer to disk.  The power fails.

During replay, all the stimuli to the program are replayed.  However, the
file writes are dumped in the bit bucket.  Block N on the disk did not get
it's updated value during play, and since writes are discarded doesn't get
the updated value during replay.  Therefor it still has the old (wrong)
value.

Cheers - Bill


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