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This article mainly explains the "zk server exception alarm and thread service shutdown mechanism", the content of the article is simple and clear, easy to learn and understand, now please follow the editor's train of thought slowly in depth, together to study and learn "zk server exception alarm and thread service shutdown mechanism"!

Mainly view ZooKeeperServer

Monitoring and server relationship class diagram

Question: when an important thread shuts down or interrupts? When will this listener be called?

Interface ZooKeeperServerListener

Void notifyStopping (String threadName, int errorCode)

Implementation class ZooKeeperServerListenerImpl

@ Override

Public void notifyStopping (String threadName, int exitCode) {

LOG.info ("Thread {} exits, error code {}", threadName, exitCode)

ZkServer.setState (State.ERROR)

}

The alarm crisis thread ZooKeeperCriticalThread inherits ZooKeeperThread

The parent class method is reimplemented, the listening notification method is called, and the service state is changed.

@ Override protected void handleException (String threadName, Throwable e) {LOG.error ("Severe unrecoverable error, from thread: {}", threadName, e); listener.notifyStopping (threadName, ExitCode.UNEXPECTED_ERROR.getValue ()); ServerMetrics.getMetrics () .UNRECOVERABLE_ERROR_COUNT.add (1);}

The processor implements ZooKeeperServerShutdownHandler

Private final CountDownLatch shutdownLatch

Void handle (State state) {if (state = = State.ERROR | | state = = State.SHUTDOWN) {shutdownLatch.countDown ();}}

Subtract 1 from shutdownLatch

1 exception handling flow

If an exception is encountered during the operation of SessionTrackerImpl

Catch (InterruptedException e) {

HandleException (this.getName (), e)

}

2 call the method handleException of the inherited class

3. Call the .notifyStopping notification method of the listener class ZooKeeperServerListener in the 3 method

4 Notification API to implement ZooKeeperServerListenerImpl specific specification processing

Set the service status to zkServer.setState (State.ERROR)

5 call the zkServer.setState method, and internally call the ZooKeeperServerShutdownHandler processor method

6 call the handle method in the processor

Void handle (State state) {

If (state = = State.ERROR | | state = = State.SHUTDOWN) {

ShutdownLatch.countDown ()

}

}

6 counter shutdown ZooKeeperServerMain registered shutdown service processor

/ / Registers shutdown handler which will be used to know the

/ / server error or shutdown state changes.

Final CountDownLatch shutdownLatch = new CountDownLatch (1)

ZkServer.registerServerShutdownHandler (new ZooKeeperServerShutdownHandler (shutdownLatch))

...

ContainerManager.start ()

/ / Watch status of ZooKeeper server. It will do a graceful shutdown

/ / if the server is not running or hits an internal error.

ShutdownLatch.await ()

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