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authorGravatar Joey Hess <joey@kitenet.net>2012-06-15 12:22:28 -0400
committerGravatar Joey Hess <joey@kitenet.net>2012-06-15 12:22:28 -0400
commita95149ac0f05d462edceac867b66b6498f1c7474 (patch)
treee76c6caf0b4e01467c891b634e0e969174d1f48b /doc
parent37a13de8ff931574174a7b64ba6a487b6ef2f754 (diff)
quarantine idea to avoid repeated lsof calls
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diff --git a/doc/design/assistant/inotify.mdwn b/doc/design/assistant/inotify.mdwn
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+++ b/doc/design/assistant/inotify.mdwn
@@ -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.
`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
would avoid this.
* Or, as a last resort, make an expensive copy of the file and add that.