org.jgroups.protocols
Class SEQUENCER

java.lang.Object
  org.jgroups.stack.Protocol
      org.jgroups.protocols.SEQUENCER

public class SEQUENCER
extends Protocol

Implementation of total order protocol using a sequencer. Consult SEQUENCER.txt for details

Author:

Bela Ban

Nested Class Summary

protected class	SEQUENCER.Flusher
static class	SEQUENCER.SequencerHeader

Field Summary

protected boolean	ack_mode When ack_mode is set, we need to wait for an ack for each forwarded message until we can send the next one
protected Promise<java.lang.Long>	ack_promise Used for each resent message to wait until the message has been received
protected long	bcast_msgs
protected Address	coord
protected long	delivered_bcasts
protected java.util.concurrent.ConcurrentMap<Address,java.util.NavigableSet<java.lang.Long>>	delivery_table
protected int	delivery_table_max_size
protected SEQUENCER.Flusher	flusher
protected boolean	flushing Set when we block all sending threads to resend all messages from forward_table
protected java.util.NavigableMap<java.lang.Long,byte[]>	forward_table Maintains messages forwarded to the coord which which no ack has been received yet.
protected long	forwarded_msgs
protected java.util.concurrent.atomic.AtomicInteger	in_flight_sends Keeps track of the threads sending messages
protected boolean	is_coord
protected Address	local_addr
protected int	num_acks
protected long	received_bcasts
protected long	received_forwards
protected boolean	running
protected java.util.concurrent.locks.Condition	send_cond
protected java.util.concurrent.locks.Lock	send_lock
protected java.util.concurrent.atomic.AtomicLong	seqno
protected int	threshold
protected View	view

Fields inherited from class org.jgroups.stack.Protocol

down_prot, ergonomics, id, log, name, stack, stats, up_prot

Constructor Summary

SEQUENCER()

Method Summary

protected void	block()
protected void	broadcast(Message msg, boolean copy, Address original_sender, long seqno, boolean resend)
protected boolean	canDeliver(Address sender, long seqno) Checks if seqno has already been received from sender.
protected void	deliver(Message msg, Event evt, SEQUENCER.SequencerHeader hdr)
java.lang.Object	down(Event evt) An event is to be sent down the stack.
java.util.Map<java.lang.String,java.lang.Object>	dumpStats()
protected void	flush(Address new_coord)
protected void	flushMessagesInForwardTable() Sends all messages currently in forward_table to the new coordinator (changing the dest field).
protected void	forward(byte[] marshalled_msg, long seqno, boolean flush)
protected void	forwardToCoord(byte[] marshalled_msg, long seqno)
long	getBroadcast()
Address	getCoordinator()
long	getForwarded()
int	getForwardTableSize()
Address	getLocalAddress()
long	getReceivedBroadcasts()
long	getReceivedForwards()
protected void	handleViewChange(View v)
boolean	isCoordinator()
java.lang.String	printStats()
void	resetStats()
void	setDeliveryTableMaxSize(int size)
void	setThreshold(int new_threshold)
void	start() This method is called on a Channel.connect(String).
protected void	startFlusher(Address new_coord)
void	stop() This method is called on a Channel.disconnect().
protected void	stopFlusher()
protected void	unblockAll()
protected void	unwrapAndDeliver(Message msg, boolean flush_ack) Unmarshal the original message (in the payload) and then pass it up (unless already delivered)
java.lang.Object	up(Event evt) An event was received from the layer below.

Methods inherited from class org.jgroups.stack.Protocol

destroy, enableStats, getConfigurableObjects, getDownProtocol, getDownServices, getId, getIdsAbove, getLevel, getName, getProtocolStack, getSocketFactory, getThreadFactory, getTransport, getUpProtocol, getUpServices, getValue, init, isErgonomics, providedDownServices, providedUpServices, requiredDownServices, requiredUpServices, resetStatistics, setDownProtocol, setErgonomics, setId, setLevel, setProtocolStack, setSocketFactory, setUpProtocol, setValue, setValues, statsEnabled

Methods inherited from class java.lang.Object

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

Field Detail

local_addr

protected Address local_addr

coord

protected volatile Address coord

view

protected volatile View view

is_coord

protected volatile boolean is_coord

seqno

protected final java.util.concurrent.atomic.AtomicLong seqno

forward_table

protected final java.util.NavigableMap<java.lang.Long,byte[]> forward_table

Maintains messages forwarded to the coord which which no ack has been received yet. Needs to be sorted so we resend them in the right order

send_lock

protected final java.util.concurrent.locks.Lock send_lock

send_cond

protected final java.util.concurrent.locks.Condition send_cond

ack_mode

protected volatile boolean ack_mode

When ack_mode is set, we need to wait for an ack for each forwarded message until we can send the next one

flushing

protected volatile boolean flushing

Set when we block all sending threads to resend all messages from forward_table

running

protected volatile boolean running

in_flight_sends

protected final java.util.concurrent.atomic.AtomicInteger in_flight_sends

Keeps track of the threads sending messages

delivery_table

protected final java.util.concurrent.ConcurrentMap<Address,java.util.NavigableSet<java.lang.Long>> delivery_table

flusher

protected volatile SEQUENCER.Flusher flusher

ack_promise

protected final Promise<java.lang.Long> ack_promise

Used for each resent message to wait until the message has been received

delivery_table_max_size

protected int delivery_table_max_size

threshold

protected int threshold

num_acks

protected int num_acks

forwarded_msgs

protected long forwarded_msgs

bcast_msgs

protected long bcast_msgs

received_forwards

protected long received_forwards

received_bcasts

protected long received_bcasts

delivered_bcasts

protected long delivered_bcasts

Constructor Detail

SEQUENCER

public SEQUENCER()

Method Detail

isCoordinator

public boolean isCoordinator()

getCoordinator

public Address getCoordinator()

getLocalAddress

public Address getLocalAddress()

getForwarded

public long getForwarded()

getBroadcast

public long getBroadcast()

getReceivedForwards

public long getReceivedForwards()

getReceivedBroadcasts

public long getReceivedBroadcasts()

getForwardTableSize

public int getForwardTableSize()

setThreshold

public void setThreshold(int new_threshold)

setDeliveryTableMaxSize

public void setDeliveryTableMaxSize(int size)

resetStats

public void resetStats()

Overrides:

resetStats in class Protocol

dumpStats

public java.util.Map<java.lang.String,java.lang.Object> dumpStats()

Overrides:

dumpStats in class Protocol

printStats

public java.lang.String printStats()

Overrides:

printStats in class Protocol

start

public void start()
           throws java.lang.Exception

Description copied from class: Protocol

This method is called on a Channel.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 class Protocol

Throws:

java.lang.Exception - Thrown if protocol cannot be started successfully. This will cause the ProtocolStack to fail, so Channel.connect(String) will throw an exception

stop

public void stop()

Description copied from class: Protocol

This method is called on a Channel.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

Overrides:

stop in class Protocol

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 using down_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 using up_prot.up().

Overrides:

down in class Protocol

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 using down_prot.down() or c) the event (or another event) is sent up the stack using up_prot.up().

Overrides:

up in class Protocol

handleViewChange

protected void handleViewChange(View v)

flush

protected void flush(Address new_coord)
              throws java.lang.InterruptedException

Throws:

java.lang.InterruptedException

flushMessagesInForwardTable

protected void flushMessagesInForwardTable()

Sends all messages currently in forward_table to the new coordinator (changing the dest field). This needs to be done, so the underlying reliable unicast protocol (e.g. UNICAST) adds these messages to its retransmission mechanism
Note that we need to resend the messages in order of their seqnos ! We also need to prevent other message from being inserted until we're done, that's why there's synchronization.
Access to the forward_table doesn't need to be synchronized as there won't be any insertions during flushing (all down-threads are blocked)

forwardToCoord

protected void forwardToCoord(byte[] marshalled_msg,
                              long seqno)

forward

protected void forward(byte[] marshalled_msg,
                       long seqno,
                       boolean flush)

broadcast

protected void broadcast(Message msg,
                         boolean copy,
                         Address original_sender,
                         long seqno,
                         boolean resend)

unwrapAndDeliver

protected void unwrapAndDeliver(Message msg,
                                boolean flush_ack)

Unmarshal the original message (in the payload) and then pass it up (unless already delivered)

Parameters:

msg -

deliver

protected void deliver(Message msg,
                       Event evt,
                       SEQUENCER.SequencerHeader hdr)

canDeliver

protected boolean canDeliver(Address sender,
                             long seqno)

Checks if seqno has already been received from sender. This weeds out duplicates. Note that this method is never called concurrently for the same sender, as the sender in NAKACK will always be the coordinator.

block

protected void block()

unblockAll

protected void unblockAll()

startFlusher

protected void startFlusher(Address new_coord)

stopFlusher

protected void stopFlusher()