Examples with CuratorWatcher org.apache.curator.framework.api.CuratorWatcher used on opensource projects

Example 1 with CuratorWatcher

use of org.apache.curator.framework.api.CuratorWatcher in project druid by druid-io.

the class LoadQueuePeon method processSegmentChangeRequest.

private void processSegmentChangeRequest() {
    if (currentlyProcessing == null) {
        if (!segmentsToDrop.isEmpty()) {
            currentlyProcessing = segmentsToDrop.firstEntry().getValue();
            log.info("Server[%s] dropping [%s]", basePath, currentlyProcessing.getSegmentIdentifier());
        } else if (!segmentsToLoad.isEmpty()) {
            currentlyProcessing = segmentsToLoad.firstEntry().getValue();
            log.info("Server[%s] loading [%s]", basePath, currentlyProcessing.getSegmentIdentifier());
        } else {
            return;
        }
        try {
            if (currentlyProcessing == null) {
                if (!stopped) {
                    log.makeAlert("Crazy race condition! server[%s]", basePath).emit();
                }
                actionCompleted();
                return;
            }
            log.info("Server[%s] processing segment[%s]", basePath, currentlyProcessing.getSegmentIdentifier());
            final String path = ZKPaths.makePath(basePath, currentlyProcessing.getSegmentIdentifier());
            final byte[] payload = jsonMapper.writeValueAsBytes(currentlyProcessing.getChangeRequest());
            curator.create().withMode(CreateMode.EPHEMERAL).forPath(path, payload);
            processingExecutor.schedule(new Runnable() {

                @Override
                public void run() {
                    try {
                        if (curator.checkExists().forPath(path) != null) {
                            failAssign(new ISE("%s was never removed! Failing this operation!", path));
                        }
                    } catch (Exception e) {
                        failAssign(e);
                    }
                }
            }, config.getLoadTimeoutDelay().getMillis(), TimeUnit.MILLISECONDS);
            final Stat stat = curator.checkExists().usingWatcher(new CuratorWatcher() {

                @Override
                public void process(WatchedEvent watchedEvent) throws Exception {
                    switch(watchedEvent.getType()) {
                        case NodeDeleted:
                            entryRemoved(watchedEvent.getPath());
                    }
                }
            }).forPath(path);
            if (stat == null) {
                final byte[] noopPayload = jsonMapper.writeValueAsBytes(new SegmentChangeRequestNoop());
                // Create a node and then delete it to remove the registered watcher.  This is a work-around for
                // a zookeeper race condition.  Specifically, when you set a watcher, it fires on the next event
                // that happens for that node.  If no events happen, the watcher stays registered foreverz.
                // Couple that with the fact that you cannot set a watcher when you create a node, but what we
                // want is to create a node and then watch for it to get deleted.  The solution is that you *can*
                // set a watcher when you check to see if it exists so, we first create the node and then set a
                // watcher on its existence.  However, if already does not exist by the time the existence check
                // returns, then the watcher that was set will never fire (nobody will ever create the node
                // again) and thus lead to a slow, but real, memory leak.  So, we create another node to cause
                // that watcher to fire and delete it right away.
                //
                // We do not create the existence watcher first, because then it will fire when we create the
                // node and we'll have the same race when trying to refresh that watcher.
                curator.create().withMode(CreateMode.EPHEMERAL).forPath(path, noopPayload);
                entryRemoved(path);
            }
        } catch (Exception e) {
            failAssign(e);
        }
    } else {
        log.info("Server[%s] skipping doNext() because something is currently loading[%s].", basePath, currentlyProcessing.getSegmentIdentifier());
    }
}