org.javagroups.protocols.pbcast
Class STABLE
java.lang.Object
|
+--org.javagroups.stack.Protocol
|
+--org.javagroups.protocols.pbcast.STABLE
- public class STABLE
- extends Protocol
Computes the broadcast messages that are stable, i.e. have been received by all members. Sends
STABLE events up the stack when this is the case. This allows NAKACK to garbage collect messages that
have been seen by all members.
Works as follows: periodically we mcast our highest seqnos (seen for each member) to the group.
A stability vector, which maintains the highest seqno for each member and initially contains no data,
is updated when such a message is received. The entry for a member P is computed set to
min(entry[P], digest[P]). When messages from all members have been received, a stability
message is mcast, which causes all members to send a STABLE event up the stack (triggering garbage collection
in the NAKACK layer).
The stable task now terminates after max_num_gossips if no messages or view changes have been sent or received
in the meantime. It will resume when messages are received. This effectively suspends sending superfluous
STABLE messages in the face of no activity.
- Author:
- Bela Ban
Fields inherited from class org.javagroups.stack.Protocol |
down_handler, down_prot, down_queue, down_thread, observer, props, stack, up_handler, up_prot, up_queue, up_thread |
Method Summary |
void |
down(Event evt)
An event is to be sent down the stack. |
java.lang.String |
getName()
|
java.util.Vector |
requiredUpServices()
List of events that are required to be answered by some layer above. |
boolean |
setProperties(java.util.Properties props)
Configures the protocol initially. |
void |
up(Event evt)
An event was received from the layer below. |
Methods inherited from class org.javagroups.stack.Protocol |
getDownProtocol, getDownQueue, getProperties, getUpProtocol, getUpQueue, init, passDown, passUp, providedDownServices, providedUpServices, receiveDownEvent, receiveUpEvent, requiredDownServices, setDownProtocol, setObserver, setPropertiesInternal, setProtocolStack, setUpProtocol, startDownHandler, startUpHandler, stopInternal |
Methods inherited from class java.lang.Object |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
STABLE
public STABLE()
getName
public java.lang.String getName()
- Overrides:
getName
in class Protocol
requiredUpServices
public java.util.Vector requiredUpServices()
- Description copied from class:
Protocol
- List of events that are required to be answered by some layer above.
- Overrides:
requiredUpServices
in class Protocol
- Following copied from class:
org.javagroups.stack.Protocol
- Returns:
- Vector (of Integers)
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 class Protocol
up
public void 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
passDown()
or c) the event (or another event) is sent up
the stack using passUp()
.
- Overrides:
up
in class Protocol
down
public void 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
passDown()
. 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 passUp()
.
- Overrides:
down
in class Protocol
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