Exception alarm and thread service shutdown mechanism of zk server
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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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