Cannot browse web UI, locked, during concurrent upload

[PVince81]

Steps

1. Enable exp file locking with redis
2. Using cadaver, PUT a file "bacon.txt" in the root
3. Add sleep(30) here https://github.com/owncloud/core/blob/master/lib/private/connector/sabre/file.php#L205 before the final rename after upload
4. PUT the file "bacon.txt" again
5. Try browsing the root folder in the web UI during the upload

Expected result

Root is browseable

Actual result

Internal server error

{"reqId":"mokcGayHlQ15XQiJB2ex","remoteAddr":"127.0.0.1","app":"index","message":"Exception: {\"Exception\":\"OCP\\\\Lock\\\\LockedException\",\"Message\":\"\\\"files\\\/c80d6549defed94752fa783bebb76dae\\\" is locked\",\"Code\":0,\"Trace\":\"#0 \\\/srv\\\/www\\\/htdocs\\\/owncloud\\\/lib\\\/private\\\/files\\\/storage\\\/common.php(633): OC\\\\Lock\\\\MemcacheLockingProvider->acquireLock('files\\\/c80d6549d...', 1)\\n#1 \\\/srv\\\/www\\\/htdocs\\\/owncloud\\\/lib\\\/private\\\/files\\\/storage\\\/wrapper\\\/wrapper.php(553): OC\\\\Files\\\\Storage\\\\Common->acquireLock('files\\\/bacon.txt', 1, Object(OC\\\\Lock\\\\MemcacheLockingProvider))\\n#2 \\\/srv\\\/www\\\/htdocs\\\/owncloud\\\/lib\\\/private\\\/files\\\/storage\\\/wrapper\\\/wrapper.php(553): OC\\\\Files\\\\Storage\\\\Wrapper\\\\Wrapper->acquireLock('files\\\/bacon.txt', 1, Object(OC\\\\Lock\\\\MemcacheLockingProvider))\\n#3 \\\/srv\\\/www\\\/htdocs\\\/owncloud\\\/lib\\\/private\\\/files\\\/cache\\\/scanner.php(133): OC\\\\Files\\\\Storage\\\\Wrapper\\\\Wrapper->acquireLock('files\\\/bacon.txt', 1, Object(OC\\\\Lock\\\\MemcacheLockingProvider))\\n#4 \\\/srv\\\/www\\\/htdocs\\\/owncloud\\\/lib\\\/private\\\/files\\\/cache\\\/scanner.php(331): OC\\\\Files\\\\Cache\\\\Scanner->scanFile('files\\\/bacon.txt', 3, 2, Array)\\n#5 \\\/srv\\\/www\\\/htdocs\\\/owncloud\\\/lib\\\/private\\\/files\\\/cache\\\/scanner.php(257): OC\\\\Files\\\\Cache\\\\Scanner->scanChildren('files', false, 3, Array)\\n#6 \\\/srv\\\/www\\\/htdocs\\\/owncloud\\\/lib\\\/private\\\/files\\\/cache\\\/watcher.php(91): OC\\\\Files\\\\Cache\\\\Scanner->scan('files', false)\\n#7 \\\/srv\\\/www\\\/htdocs\\\/owncloud\\\/lib\\\/private\\\/files\\\/view.php(1171): OC\\\\Files\\\\Cache\\\\Watcher->checkUpdate('files', Array)\\n#8 \\\/srv\\\/www\\\/htdocs\\\/owncloud\\\/lib\\\/private\\\/files\\\/filesystem.php(861): OC\\\\Files\\\\View->getFileInfo('\\\/', false)\\n#9 \\\/srv\\\/www\\\/htdocs\\\/owncloud\\\/apps\\\/files\\\/index.php(84): OC\\\\Files\\\\Filesystem::getFileInfo('\\\/', false)\\n#10 \\\/srv\\\/www\\\/htdocs\\\/owncloud\\\/lib\\\/private\\\/route\\\/route.php(153) : runtime-created function(1): require_once('\\\/srv\\\/www\\\/htdocs...')\\n#11 [internal function]: __lambda_func(Array)\\n#12 \\\/srv\\\/www\\\/htdocs\\\/owncloud\\\/lib\\\/private\\\/route\\\/router.php(274): call_user_func('\\\\x00lambda_216', Array)\\n#13 \\\/srv\\\/www\\\/htdocs\\\/owncloud\\\/lib\\\/base.php(867): OC\\\\Route\\\\Router->match('\\\/apps\\\/files\\\/')\\n#14 \\\/srv\\\/www\\\/htdocs\\\/owncloud\\\/index.php(40): OC::handleRequest()\\n#15 {main}\",\"File\":\"\\\/srv\\\/www\\\/htdocs\\\/owncloud\\\/lib\\\/private\\\/lock\\\/memcachelockingprovider.php\",\"Line\":70}","level":4,"time":"2015-06-17T15:41:36+00:00","method":"GET","url":"\/owncloud\/index.php\/apps\/files\/"}

Happens on latest master (bfa716a)

@icewind1991 seems one of the locks is too "strong" ?

[PVince81]

Regression introduced by the scanner PR regarding locking: #16729 (comment)

[icewind1991]

@icewind1991 seems one of the locks is too "strong" ?

Not to strong, it's locked since it can't scan the newly created file.

What is the exact expected behavior? having the root folder without the new file in it?

We could catch the locked exception in the cache watcher and return the existing (slightly outdated) cache data of the folder.

[PVince81]

Hmmm good point.
On the one hand I'd say show the file but downloading it fails because of the lock.
But then if we don't know how big it is, what size do we show ? 0 ?

Not showing it might be fine too. But beware of overwrites. Might be easier to always show it.

[icewind1991]

But beware of overwrites.

Wont happen due to locking

[PVince81]

This PR fixes it #16963

[PVince81]

Fixed by #16963