groovyx.gpars.dataflow.operator.component
Class GracefulShutdownMonitor

java.lang.Object
  groovyx.gpars.dataflow.operator.component.GracefulShutdownMonitor

All Implemented Interfaces:

OperatorStateMonitor

public final class GracefulShutdownMonitor
extends java.lang.Object
implements OperatorStateMonitor

The monitor will orchestrate a graceful shutdown, when its shutdownNetwork() method is called. For this mechanism to work, all selectors/operators in the network have to have their own instance of GracefulShutdownListener added and these listeners have to share the same GracefulShutdownMonitor instance. Each listener observes the activity in the input channels of its corresponding operator/selector. Upon graceful shutdown initialization, the listeners also start watching the state of their operators/selectors. The GracefulShutdownMonitor then repeatedly watches, whether listeners report activity in the operators. When the activity ceases, the monitor will poll all listeners about the state of their operator/selector and its input channels. If all listeners report no activity and no incoming messages, the monitor can safely terminate all operators.

Author:

Vaclav Pech

Field Summary

private static long	DEFAULT_DELAY
private long	delay
private java.util.Collection<GracefulShutdownListener>	listeners All listeners that watch the operators/selectors in the network
private java.util.concurrent.atomic.AtomicBoolean	notificationArrivedFlag Indicates, whether some activity has been reported since last time
private DataflowVariable<java.lang.Boolean>	result The final latch that indicates the network has been shutdown
private boolean	shutdownFlag Indicates whether shutdown has been initialized
private java.util.Timer	timer A times used to repeatedly poll the state of the network

Constructor Summary

GracefulShutdownMonitor()
Uses the default timer delay

GracefulShutdownMonitor(long delay)
Allows to use a customized delay

Method Summary

private boolean	checkWhetherAnyEventsHaveArrived() Checks the notification flag whether there has been some activity since last timer run.
(package private) void	onTimer() Checks, whether the network is no longer active.
void	registerProcessorListener(GracefulShutdownListener listener) Invoked by GracefulShutdownListeners, which listen on operators/selectors for lifecycle events, to get registered with the monitor.
Promise<java.lang.Boolean>	shutdownNetwork() Initializes the shutdown process.
private void	schedule() Clears the notification flag so as we know whether some activity happens between subsequent checks.
void	stateChanged() Invoked whenever a processor changes state

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

DEFAULT_DELAY

private static final long DEFAULT_DELAY

See Also:

Constant Field Values

delay

private final long delay

shutdownFlag

private boolean shutdownFlag

Indicates whether shutdown has been initialized

notificationArrivedFlag

private final java.util.concurrent.atomic.AtomicBoolean notificationArrivedFlag

Indicates, whether some activity has been reported since last time

result

private final DataflowVariable<java.lang.Boolean> result

The final latch that indicates the network has been shutdown

listeners

private final java.util.Collection<GracefulShutdownListener> listeners

All listeners that watch the operators/selectors in the network

timer

private final java.util.Timer timer

A times used to repeatedly poll the state of the network

Constructor Detail

GracefulShutdownMonitor

public GracefulShutdownMonitor()

Uses the default timer delay

GracefulShutdownMonitor

public GracefulShutdownMonitor(long delay)

Allows to use a customized delay

Parameters:

delay - A timeout in milliseconds to wait between two subsequent polls on processors' state. Lower values will reduce the wait time for network shutdown, but maz have impact on the performance when the shutdown process gets initialized.

Method Detail

stateChanged

public void stateChanged()

Invoked whenever a processor changes state

Specified by:

stateChanged in interface OperatorStateMonitor

registerProcessorListener

public void registerProcessorListener(GracefulShutdownListener listener)

Invoked by GracefulShutdownListeners, which listen on operators/selectors for lifecycle events, to get registered with the monitor. The monitor will query these registered listeners about their respective operator/selector state when performing graceful shutdown.

Specified by:

registerProcessorListener in interface OperatorStateMonitor

Parameters:

listener - The listener to register

shutdownNetwork

public Promise<java.lang.Boolean> shutdownNetwork()

Initializes the shutdown process. New listeners cannot be registered after this point. New messages should not enter the dataflow network from the outside, since this may prevent the network from terminating.

Returns:

A Promise, which may be used to wait for or get notified about the shutdown success.

onTimer

void onTimer()

Checks, whether the network is no longer active. To reduce effect on system performance, cheap criteria are being checked first.

checkWhetherAnyEventsHaveArrived

private boolean checkWhetherAnyEventsHaveArrived()

Checks the notification flag whether there has been some activity since last timer run.

Returns:

True, if events have been registered since last time, false otherwise.

schedule

private void schedule()

Clears the notification flag so as we know whether some activity happens between subsequent checks. Schedules the timer to run again after the delay set on the monitor.