Package org.jgroups.protocols.pbcast
Class FLUSH
- java.lang.Object
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- org.jgroups.stack.Protocol
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- org.jgroups.protocols.pbcast.FLUSH
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public class FLUSH extends Protocol
Flush, as it name implies, forces group members to flush their pending messages while blocking them to send any additional messages. The process of flushing acquiesces the group so that state transfer or a join can be done. It is also called stop-the-world model as nobody will be able to send messages while a flush is in process.Flush is needed for:
(1) State transfer. When a member requests state transfer, the coordinator tells everyone to stop sending messages and waits for everyone's ack. Then it asks the application for its state and ships it back to the requester. After the requester has received and set the state successfully, the coordinator tells everyone to resume sending messages.
(2) View changes (e.g.a join). Before installing a new view V2, flushing would ensure that all messages *sent* in the current view V1 are indeed *delivered* in V1, rather than in V2 (in all non-faulty members). This is essentially Virtual Synchrony.
- Since:
- 2.4
- Version:
- $Id$
- Author:
- Vladimir Blagojevic
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Nested Class Summary
Nested Classes Modifier and Type Class Description static class
FLUSH.FlushHeader
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Constructor Summary
Constructors Constructor Description FLUSH()
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description java.lang.Object
down(Event evt)
An event is to be sent down the stack.double
getAverageFlushDuration()
java.lang.String
getName()
int
getNumberOfFlushes()
long
getStartFlushTimeout()
long
getTotalTimeInFlush()
java.util.Vector<java.lang.Integer>
providedDownServices()
List of events that are provided to layers below (they will be handled when sent down from below).boolean
setProperties(java.util.Properties props)
Configures the protocol initially.void
setStartFlushTimeout(long start_flush_timeout)
void
start()
This method is called on aChannel.connect(String)
.boolean
startFlush()
void
stop()
This method is called on aChannel.disconnect()
.void
stopFlush()
java.lang.Object
up(Event evt)
An event was received from the layer below.-
Methods inherited from class org.jgroups.stack.Protocol
destroy, downThreadEnabled, dumpStats, enableStats, getDownProtocol, getProperties, getProtocolStack, getThreadFactory, getTransport, getUpProtocol, init, printStats, providedUpServices, requiredDownServices, requiredUpServices, resetStats, setDownProtocol, setPropertiesInternal, setProtocolStack, setUpProtocol, statsEnabled, upThreadEnabled
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Field Detail
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NAME
public static final java.lang.String NAME
- See Also:
- Constant Field Values
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Method Detail
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getStartFlushTimeout
public long getStartFlushTimeout()
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setStartFlushTimeout
public void setStartFlushTimeout(long start_flush_timeout)
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setProperties
public boolean setProperties(java.util.Properties props)
Description copied from class:Protocol
Configures the protocol initially. A configuration string consists of name=value items, separated by a ';' (semicolon), e.g.:"loopback=false;unicast_inport=4444"
- Overrides:
setProperties
in classProtocol
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start
public void start() throws java.lang.Exception
Description copied from class:Protocol
This method is called on aChannel.connect(String)
. Starts work. Protocols are connected and queues are ready to receive events. Will be called from bottom to top. This call will replace the START and START_OK events.- Overrides:
start
in classProtocol
- Throws:
java.lang.Exception
- Thrown if protocol cannot be started successfully. This will cause the ProtocolStack to fail, soChannel.connect(String)
will throw an exception
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stop
public void stop()
Description copied from class:Protocol
This method is called on aChannel.disconnect()
. Stops work (e.g. by closing multicast socket). Will be called from top to bottom. This means that at the time of the method invocation the neighbor protocol below is still working. This method will replace the STOP, STOP_OK, CLEANUP and CLEANUP_OK events. The ProtocolStack guarantees that when this method is called all messages in the down queue will have been flushed
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getAverageFlushDuration
public double getAverageFlushDuration()
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getTotalTimeInFlush
public long getTotalTimeInFlush()
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getNumberOfFlushes
public int getNumberOfFlushes()
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startFlush
public boolean startFlush()
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stopFlush
public void stopFlush()
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down
public java.lang.Object down(Event evt)
Description copied from class:Protocol
An event is to be sent down the stack. The layer may want to examine its type and perform some action on it, depending on the event's type. If the event is a message MSG, then the layer may need to add a header to it (or do nothing at all) before sending it down the stack usingdown_prot.down()
. In case of a GET_ADDRESS event (which tries to retrieve the stack's address from one of the bottom layers), the layer may need to send a new response event back up the stack usingup_prot.up()
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up
public java.lang.Object up(Event evt)
Description copied from class:Protocol
An event was received from the layer below. Usually the current layer will want to examine the event type and - depending on its type - perform some computation (e.g. removing headers from a MSG event type, or updating the internal membership list when receiving a VIEW_CHANGE event). Finally the event is either a) discarded, or b) an event is sent down the stack usingdown_prot.down()
or c) the event (or another event) is sent up the stack usingup_prot.up()
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providedDownServices
public java.util.Vector<java.lang.Integer> providedDownServices()
Description copied from class:Protocol
List of events that are provided to layers below (they will be handled when sent down from below).- Overrides:
providedDownServices
in classProtocol
- Returns:
- Vector
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