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quarantine idea to avoid repeated lsof calls

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Joey Hess 2012-06-15 12:22:28 -04:00
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doc/design/assistant/inotify.mdwn
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@ -19,6 +19,19 @@ There is a `watch` branch in git that adds the command.
* Somehow track or detect if a file is open for write by any processes. * Somehow track or detect if a file is open for write by any processes.
`lsof` could be used, although it would be a little slow. `lsof` could be used, although it would be a little slow.
Here's one way to avoid the slowdown: When a file is being added,
set it read-only, and hard-link it into a quarantine directory,
remembering both filenames.
Then use the batch change mode code to detect batch adds and bundle
them together.
Just before committing, lsof the quarantine directory. Any files in
it that are still open for write can just have their write bit turned
back on and be deleted from quarantine, to be handled when their writer
closes. Files that pass quarantine get added as usual. This avoids
repeated lsof calls slowing down adds, but does add a constant factor
overhead (0.25 seconds lsof call) before any add gets committed.
* Or, when possible, making a copy on write copy before adding the file * Or, when possible, making a copy on write copy before adding the file
would avoid this. would avoid this.
* Or, as a last resort, make an expensive copy of the file and add that. * Or, as a last resort, make an expensive copy of the file and add that.