FD

java.lang.Object
- org.jgroups.stack.Protocol
- - org.jgroups.protocols.FD

Direct Known Subclasses:

FD_PING
```
public class FD
extends Protocol
```
Failure detection based on simple heartbeat protocol. Regularly polls members for liveness. Multicasts SUSPECT messages when a member is not reachable. The simple algorithms works as follows: the membership is known and ordered. Each HB protocol periodically sends an 'are-you-alive' message to its *neighbor*. A neighbor is the next in rank in the membership list, which is recomputed upon a view change. When a response hasn't been received for n milliseconds and m tries, the corresponding member is suspected (and eventually excluded if faulty).
FD starts when it detects (in a view change notification) that there are at least 2 members in the group. It stops running when the membership drops below 2.
When a message is received from the monitored neighbor member, it causes the pinger thread to 'skip' sending the next are-you-alive message. Thus, traffic is reduced.

Author:

Bela Ban

Nested Class Summary

Nested Classes
Modifier and Type	Class and Description
`protected class`	`FD.Broadcaster` Task that periodically broadcasts a list of suspected members to the group.
`protected class`	`FD.BroadcastTask`
`static class`	`FD.FdHeader`
`protected class`	`FD.Monitor` Task which periodically checks of the last_ack from ping_dest exceeded timeout and - if yes - broadcasts a SUSPECT message

Field Summary

Fields
Modifier and Type	Field and Description
`protected FD.Broadcaster`	`bcast_task` Transmits SUSPECT message until view change or UNSUSPECT is received
`protected long`	`last_ack`
`protected Address`	`local_addr`
`protected java.util.concurrent.locks.Lock`	`lock`
`protected int`	`max_tries`
`protected java.util.List<Address>`	`members`
`protected java.util.concurrent.Future<?>`	`monitor_future`
`protected int`	`num_heartbeats`
`protected int`	`num_suspect_events`
`protected java.util.concurrent.atomic.AtomicInteger`	`num_tries`
`protected Address`	`ping_dest`
`protected java.util.List<Address>`	`pingable_mbrs` Members from which we select ping_dest.
`protected BoundedList<java.lang.String>`	`suspect_history`
`protected long`	`timeout`
`protected TimeScheduler`	`timer`

Fields inherited from class org.jgroups.stack.Protocol
after_creation_hook, down_prot, ergonomics, id, log, name, stack, stats, up_prot

Constructor Summary

Constructors
Constructor and Description

FD()

Constructors
Constructor and Description
`FD()`

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`protected void`	`computePingDest(Address remove)` Computes pingable_mbrs (based on the current membership and the suspected members) and ping_dest
`java.lang.Object`	`down(Event evt)` An event is to be sent down the stack.
`int`	`getCurrentNumTries()`
`java.lang.String`	`getLocalAddress()`
`int`	`getMaxTries()`
`java.lang.String`	`getMembers()`
`int`	`getNumberOfHeartbeatsSent()`
`int`	`getNumSuspectEventsGenerated()`
`java.lang.String`	`getPingableMembers()`
`java.lang.String`	`getPingDest()`
`protected Address`	`getPingDest(java.util.List<Address> mbrs)`
`long`	`getTimeout()`
`void`	`init()` Called after instance has been created (null constructor) and before protocol is started.
`boolean`	`isMonitorRunning()`
`java.lang.String`	`printSuspectHistory()`
`void`	`resetStats()`
`protected void`	`sendHeartbeatResponse(Address dest)`
`void`	`setMaxTries(int max_tries)`
`void`	`setTimeout(long timeout)`
`void`	`startFailureDetection()`
`protected void`	`startMonitor()` Requires lock to held by caller
`void`	`stop()` This method is called on a `Channel.disconnect()`.
`void`	`stopFailureDetection()`
`protected void`	`stopMonitor()` Requires lock to be held by caller
`protected void`	`unsuspect(Address mbr)`
`java.lang.Object`	`up(Event evt)` An event was received from the layer below.
`void`	`up(MessageBatch batch)` Sends up a multiple messages in a `MessageBatch`.
`protected void`	`updateTimestamp(Address sender)`

Methods inherited from class org.jgroups.stack.Protocol
accept, afterCreationHook, destroy, dumpStats, enableStats, getConfigurableObjects, getDownProtocol, getDownServices, getId, getIdsAbove, getLevel, getLog, getName, getProtocolStack, getSocketFactory, getThreadFactory, getTransport, getUpProtocol, getUpServices, getValue, isErgonomics, level, parse, printStats, providedDownServices, providedUpServices, requiredDownServices, requiredUpServices, resetStatistics, setDownProtocol, setErgonomics, setId, setLevel, setProtocolStack, setSocketFactory, setUpProtocol, setValue, setValues, start, statsEnabled

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - timeout
```
protected long timeout
```
  - max_tries
```
protected int max_tries
```
  - num_heartbeats
```
protected int num_heartbeats
```
  - num_suspect_events
```
protected int num_suspect_events
```
  - suspect_history
```
protected final BoundedList<java.lang.String> suspect_history
```
  - local_addr
```
protected Address local_addr
```
  - last_ack
```
protected volatile long last_ack
```
  - num_tries
```
protected final java.util.concurrent.atomic.AtomicInteger num_tries
```
  - lock
```
protected final java.util.concurrent.locks.Lock lock
```
  - ping_dest
```
protected volatile Address ping_dest
```
  - members
```
protected final java.util.List<Address> members
```
  - pingable_mbrs
```
protected final java.util.List<Address> pingable_mbrs
```
    Members from which we select ping_dest. Copy of members minus the suspected members
  - timer
```
protected TimeScheduler timer
```
  - monitor_future
```
protected java.util.concurrent.Future<?> monitor_future
```
  - bcast_task
```
protected final FD.Broadcaster bcast_task
```
    Transmits SUSPECT message until view change or UNSUSPECT is received
- Constructor Detail
  - FD
```
public FD()
```
- Method Detail
  - getLocalAddress
```
public java.lang.String getLocalAddress()
```
  - getMembers
```
public java.lang.String getMembers()
```
  - getPingableMembers
```
public java.lang.String getPingableMembers()
```
  - getPingDest
```
public java.lang.String getPingDest()
```
  - getNumberOfHeartbeatsSent
```
public int getNumberOfHeartbeatsSent()
```
  - getNumSuspectEventsGenerated
```
public int getNumSuspectEventsGenerated()
```
  - getTimeout
```
public long getTimeout()
```
  - setTimeout
```
public void setTimeout(long timeout)
```
  - getMaxTries
```
public int getMaxTries()
```
  - setMaxTries
```
public void setMaxTries(int max_tries)
```
  - getCurrentNumTries
```
public int getCurrentNumTries()
```
  - printSuspectHistory
```
public java.lang.String printSuspectHistory()
```
  - resetStats
```
public void resetStats()
```
    Overrides:
    
    resetStats in class Protocol
  - init
```
public void init()
          throws java.lang.Exception
```
    Description copied from class: Protocol
    
    Called after instance has been created (null constructor) and before protocol is started. Properties are already set. Other protocols are not yet connected and events cannot yet be sent.
    
    Overrides:
    
    init in class Protocol
    
    Throws:
    
    java.lang.Exception - Thrown if protocol cannot be initialized successfully. This will cause the ProtocolStack to fail, so the channel constructor 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
  - getPingDest
```
protected Address getPingDest(java.util.List<Address> mbrs)
```
  - stopFailureDetection
```
public void stopFailureDetection()
```
  - startFailureDetection
```
public void startFailureDetection()
```
  - startMonitor
```
protected void startMonitor()
```
    Requires lock to held by caller
  - stopMonitor
```
protected void stopMonitor()
```
    Requires lock to be held by caller
  - isMonitorRunning
```
public boolean isMonitorRunning()
```
  - 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
  - up
```
public void up(MessageBatch batch)
```
    Description copied from class: Protocol
    
    Sends up a multiple messages in a MessageBatch. The sender of the batch is always the same, and so is the destination (null == multicast messages). Messages in a batch can be OOB messages, regular messages, or mixed messages, although the transport itself will create initial MessageBatches that contain only either OOB or regular messages.
    The default processing below sends messages up the stack individually, based on a matching criteria (calling Protocol.accept(org.jgroups.Message)), and - if true - calls Protocol.up(org.jgroups.Event) for that message and removes the message. If the batch is not empty, it is passed up, or else it is dropped.
    Subclasses should check if there are any messages destined for them (e.g. using MessageBatch.getMatchingMessages(short,boolean)), then possibly remove and process them and finally pass the batch up to the next protocol. Protocols can also modify messages in place, e.g. ENCRYPT could decrypt all encrypted messages in the batch, not remove them, and pass the batch up when done.
    
    Overrides:
    
    up in class Protocol
    
    Parameters:
    
    batch - The message batch
  - 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
  - sendHeartbeatResponse
```
protected void sendHeartbeatResponse(Address dest)
```
  - unsuspect
```
protected void unsuspect(Address mbr)
```
  - updateTimestamp
```
protected void updateTimestamp(Address sender)
```
  - computePingDest
```
protected void computePingDest(Address remove)
```
    Computes pingable_mbrs (based on the current membership and the suspected members) and ping_dest
    
    Parameters:
    
    remove - The member to be removed from pingable_mbrs

Class FD

Nested Class Summary

Field Summary

Fields inherited from class org.jgroups.stack.Protocol

Constructor Summary

Method Summary

Methods inherited from class org.jgroups.stack.Protocol

Methods inherited from class java.lang.Object

Field Detail

timeout

max_tries

num_heartbeats

num_suspect_events

suspect_history

local_addr

last_ack

num_tries

lock

ping_dest

members

pingable_mbrs

timer

monitor_future

bcast_task

Constructor Detail

FD

Method Detail

getLocalAddress

getMembers

getPingableMembers

getPingDest

getNumberOfHeartbeatsSent

getNumSuspectEventsGenerated

getTimeout

setTimeout

getMaxTries

setMaxTries

getCurrentNumTries

printSuspectHistory

resetStats

init

stop

getPingDest

stopFailureDetection

startFailureDetection

startMonitor

stopMonitor

isMonitorRunning

up

up

down

sendHeartbeatResponse

unsuspect

updateTimestamp

computePingDest