/**
* If clocks in sync, then acquires the oldest expired lock Else, on first call, just remembers
* the oldest expired lock, on next call check if the lock is updated. if not updated then
* acquires the lock
*
* @return a lock object
* @throws IOException
*/
private FileLock getOldestExpiredLock() throws IOException {
// 1 - acquire lock on dir
DirLock dirlock = DirLock.tryLock(hdfs, lockDirPath);
if (dirlock == null) {
dirlock = DirLock.takeOwnershipIfStale(hdfs, lockDirPath, lockTimeoutSec);
if (dirlock == null) {
LOG.debug("Spout {} could not take over ownership of DirLock for {}", spoutId, lockDirPath);
return null;
}
LOG.debug(
"Spout {} now took over ownership of abandoned DirLock for {}", spoutId, lockDirPath);
} else {
LOG.debug("Spout {} now owns DirLock for {}", spoutId, lockDirPath);
}
try {
// 2 - if clocks are in sync then simply take ownership of the oldest expired lock
if (clocksInSync) {
return FileLock.acquireOldestExpiredLock(hdfs, lockDirPath, lockTimeoutSec, spoutId);
}
// 3 - if clocks are not in sync ..
if (lastExpiredLock == null) {
// just make a note of the oldest expired lock now and check if its still unmodified after
// lockTimeoutSec
lastExpiredLock = FileLock.locateOldestExpiredLock(hdfs, lockDirPath, lockTimeoutSec);
lastExpiredLockTime = System.currentTimeMillis();
return null;
}
// see if lockTimeoutSec time has elapsed since we last selected the lock file
if (hasExpired(lastExpiredLockTime)) {
return null;
}
// If lock file has expired, then own it
FileLock.LogEntry lastEntry = FileLock.getLastEntry(hdfs, lastExpiredLock.getKey());
if (lastEntry.equals(lastExpiredLock.getValue())) {
FileLock result =
FileLock.takeOwnership(hdfs, lastExpiredLock.getKey(), lastEntry, spoutId);
lastExpiredLock = null;
return result;
} else {
// if lock file has been updated since last time, then leave this lock file alone
lastExpiredLock = null;
return null;
}
} finally {
dirlock.release();
LOG.debug("Released DirLock {}, SpoutID {} ", dirlock.getLockFile(), spoutId);
}
}
