Apache Tomcat 6.0.39

org.apache.catalina.tribes
Interface Channel

All Known Subinterfaces:
ManagedChannel
All Known Implementing Classes:
GroupChannel

public interface Channel

Channel interface
A channel is a representation of a group of nodes all participating in some sort of communication with each other.
The channel is the main API class for Tribes, this is essentially the only class that an application needs to be aware of. Through the channel the application can:
1. send messages
2. receive message (by registering a ChannelListener
3. get all members of the group getMembers()
4. receive notifications of members added and members disappeared by registerering a MembershipListener

The channel has 5 major components:
1. Data receiver, with a built in thread pool to receive messages from other peers
2. Data sender, an implementation for sending data using NIO or java.io
3. Membership listener,listens for membership broadcasts
4. Membership broadcaster, broadcasts membership pings.
5. Channel interceptors, the ability to manipulate messages as they are sent or arrive

The channel layout is:


  ChannelListener_1..ChannelListener_N MembershipListener_1..MembershipListener_N [Application Layer]
            \          \                  /                   /
             \          \                /                   /
              \          \              /                   /
               \          \            /                   /
                \          \          /                   /
                 \          \        /                   /
                  ---------------------------------------
                                  |
                                  |
                               Channel
                                  |
                         ChannelInterceptor_1
                                  |                                               [Channel stack]
                         ChannelInterceptor_N
                                  |
                             Coordinator (implements MessageListener,MembershipListener,ChannelInterceptor)
                          --------------------
                         /        |           \ 
                        /         |            \
                       /          |             \
                      /           |              \
                     /            |               \
           MembershipService ChannelSender ChannelReceiver                        [IO layer]
 
For example usage @see org.apache.catalina.tribes.group.GroupChannel

Version:
$Id: Channel.java 939515 2010-04-29 23:59:49Z kkolinko $
Author:
Filip Hanik

Field Summary
static int DEFAULT
          Start and stop sequences can be controlled by these constants This allows you to start separate components of the channel
DEFAULT - starts or stops all components in the channel
static int MBR_RX_SEQ
          Start and stop sequences can be controlled by these constants This allows you to start separate components of the channel
MBR_RX_SEQ - starts or stops the membership listener.
static int MBR_TX_SEQ
          Start and stop sequences can be controlled by these constants This allows you to start separate components of the channel
MBR_TX_SEQ - starts or stops the membership broadcaster.
static int SEND_OPTIONS_ASYNCHRONOUS
          Send options, when a message is sent, it can have an option flag to trigger certain behavior.
static int SEND_OPTIONS_BYTE_MESSAGE
          Send options, when a message is sent, it can have an option flag to trigger certain behavior.
static int SEND_OPTIONS_DEFAULT
          Send options, when a message is sent, it can have an option flag to trigger certain behavior.
static int SEND_OPTIONS_SECURE
          Send options, when a message is sent, it can have an option flag to trigger certain behavior.
static int SEND_OPTIONS_SYNCHRONIZED_ACK
          Send options, when a message is sent, it can have an option flag to trigger certain behavior.
static int SEND_OPTIONS_USE_ACK
          Send options, when a message is sent, it can have an option flag to trigger certain behavior.
static int SND_RX_SEQ
          Start and stop sequences can be controlled by these constants This allows you to start separate components of the channel
SND_RX_SEQ - starts or stops the data receiver.
static int SND_TX_SEQ
          Start and stop sequences can be controlled by these constants This allows you to start separate components of the channel
SND_TX_SEQ - starts or stops the data sender.
 
Method Summary
 void addChannelListener(ChannelListener listener)
          Add a channel listener, this is a callback object when messages are received
If the channel listener implements the Heartbeat interface the heartbeat() method will be invoked when the heartbeat runs on the channel
 void addInterceptor(ChannelInterceptor interceptor)
          Adds an interceptor to the channel message chain.
 void addMembershipListener(MembershipListener listener)
          Add a membership listener, will get notified when a new member joins, leaves or crashes
If the membership listener implements the Heartbeat interface the heartbeat() method will be invoked when the heartbeat runs on the channel
 Member getLocalMember(boolean incAlive)
          Return the member that represents this node.
 Member getMember(Member mbr)
          Returns the member from the membership service with complete and recent data.
 Member[] getMembers()
          Get all current group members
 boolean hasMembers()
          Returns true if there are any members in the group, this call is the same as getMembers().length>0
 void heartbeat()
          Sends a heart beat through the interceptor stacks Use this method to alert interceptors and other components to clean up garbage, timed out messages etc.
 void removeChannelListener(ChannelListener listener)
          remove a channel listener, listeners are removed based on Object.hashCode and Object.equals
 void removeMembershipListener(MembershipListener listener)
          remove a membership listener, listeners are removed based on Object.hashCode and Object.equals
 UniqueId send(Member[] destination, java.io.Serializable msg, int options)
          Send a message to one or more members in the cluster
 UniqueId send(Member[] destination, java.io.Serializable msg, int options, ErrorHandler handler)
          Send a message to one or more members in the cluster
 void setHeartbeat(boolean enable)
          Enables or disables internal heartbeat.
 void start(int svc)
          Starts up the channel.
 void stop(int svc)
          Shuts down the channel.
 

Field Detail

DEFAULT

static final int DEFAULT
Start and stop sequences can be controlled by these constants This allows you to start separate components of the channel
DEFAULT - starts or stops all components in the channel

See Also:
start(int), stop(int), Constant Field Values

SND_RX_SEQ

static final int SND_RX_SEQ
Start and stop sequences can be controlled by these constants This allows you to start separate components of the channel
SND_RX_SEQ - starts or stops the data receiver. Start means opening a server socket in case of a TCP implementation

See Also:
start(int), stop(int), Constant Field Values

SND_TX_SEQ

static final int SND_TX_SEQ
Start and stop sequences can be controlled by these constants This allows you to start separate components of the channel
SND_TX_SEQ - starts or stops the data sender. This should not open any sockets, as sockets are opened on demand when a message is being sent

See Also:
start(int), stop(int), Constant Field Values

MBR_RX_SEQ

static final int MBR_RX_SEQ
Start and stop sequences can be controlled by these constants This allows you to start separate components of the channel
MBR_RX_SEQ - starts or stops the membership listener. In a multicast implementation this will open a datagram socket and join a group and listen for membership messages members joining

See Also:
start(int), stop(int), Constant Field Values

MBR_TX_SEQ

static final int MBR_TX_SEQ
Start and stop sequences can be controlled by these constants This allows you to start separate components of the channel
MBR_TX_SEQ - starts or stops the membership broadcaster. In a multicast implementation this will open a datagram socket and join a group and broadcast the local member information

See Also:
start(int), stop(int), Constant Field Values

SEND_OPTIONS_BYTE_MESSAGE

static final int SEND_OPTIONS_BYTE_MESSAGE
Send options, when a message is sent, it can have an option flag to trigger certain behavior. Most flags are used to trigger channel interceptors as the message passes through the channel stack.
However, there are five default flags that every channel implementation must implement
SEND_OPTIONS_BYTE_MESSAGE - The message is a pure byte message and no marshalling or unmarshalling will be performed.

See Also:
send(Member[], Serializable , int), send(Member[], Serializable, int, ErrorHandler), Constant Field Values

SEND_OPTIONS_USE_ACK

static final int SEND_OPTIONS_USE_ACK
Send options, when a message is sent, it can have an option flag to trigger certain behavior. Most flags are used to trigger channel interceptors as the message passes through the channel stack.
However, there are five default flags that every channel implementation must implement
SEND_OPTIONS_USE_ACK - Message is sent and an ACK is received when the message has been received by the recipient
If no ack is received, the message is not considered successful

See Also:
send(Member[], Serializable , int), send(Member[], Serializable, int, ErrorHandler), Constant Field Values

SEND_OPTIONS_SYNCHRONIZED_ACK

static final int SEND_OPTIONS_SYNCHRONIZED_ACK
Send options, when a message is sent, it can have an option flag to trigger certain behavior. Most flags are used to trigger channel interceptors as the message passes through the channel stack.
However, there are five default flags that every channel implementation must implement
SEND_OPTIONS_SYNCHRONIZED_ACK - Message is sent and an ACK is received when the message has been received and processed by the recipient
If no ack is received, the message is not considered successful

See Also:
send(Member[], Serializable , int), send(Member[], Serializable, int, ErrorHandler), Constant Field Values

SEND_OPTIONS_ASYNCHRONOUS

static final int SEND_OPTIONS_ASYNCHRONOUS
Send options, when a message is sent, it can have an option flag to trigger certain behavior. Most flags are used to trigger channel interceptors as the message passes through the channel stack.
However, there are five default flags that every channel implementation must implement
SEND_OPTIONS_ASYNCHRONOUS - Message is sent and an ACK is received when the message has been received and processed by the recipient
If no ack is received, the message is not considered successful

See Also:
send(Member[], Serializable , int), send(Member[], Serializable, int, ErrorHandler), Constant Field Values

SEND_OPTIONS_SECURE

static final int SEND_OPTIONS_SECURE
Send options, when a message is sent, it can have an option flag to trigger certain behavior. Most flags are used to trigger channel interceptors as the message passes through the channel stack.
However, there are five default flags that every channel implementation must implement
SEND_OPTIONS_SECURE - Message is sent over an encrypted channel

See Also:
send(Member[], Serializable , int), send(Member[], Serializable, int, ErrorHandler), Constant Field Values

SEND_OPTIONS_DEFAULT

static final int SEND_OPTIONS_DEFAULT
Send options, when a message is sent, it can have an option flag to trigger certain behavior. Most flags are used to trigger channel interceptors as the message passes through the channel stack.
However, there are five default flags that every channel implementation must implement
SEND_OPTIONS_DEFAULT - the default sending options, just a helper variable.
The default is int SEND_OPTIONS_DEFAULT = SEND_OPTIONS_USE_ACK;

See Also:
SEND_OPTIONS_USE_ACK, send(Member[], Serializable , int), send(Member[], Serializable, int, ErrorHandler), Constant Field Values
Method Detail

addInterceptor

void addInterceptor(ChannelInterceptor interceptor)
Adds an interceptor to the channel message chain.

Parameters:
interceptor - ChannelInterceptor

start

void start(int svc)
           throws ChannelException
Starts up the channel. This can be called multiple times for individual services to start The svc parameter can be the logical or value of any constants

Parameters:
svc - int value of
DEFAULT - will start all services
MBR_RX_SEQ - starts the membership receiver
MBR_TX_SEQ - starts the membership broadcaster
SND_TX_SEQ - starts the replication transmitter
SND_RX_SEQ - starts the replication receiver
Note: In order for the membership broadcaster to transmit the correct information, it has to be started after the replication receiver.
Throws:
ChannelException - if a startup error occurs or the service is already started or an error occurs.

stop

void stop(int svc)
          throws ChannelException
Shuts down the channel. This can be called multiple times for individual services to shutdown The svc parameter can be the logical or value of any constants

Parameters:
svc - int value of
DEFAULT - will shutdown all services
MBR_RX_SEQ - stops the membership receiver
MBR_TX_SEQ - stops the membership broadcaster
SND_TX_SEQ - stops the replication transmitter
SND_RX_SEQ - stops the replication receiver
Throws:
ChannelException - if a startup error occurs or the service is already stopped or an error occurs.

send

UniqueId send(Member[] destination,
              java.io.Serializable msg,
              int options)
              throws ChannelException
Send a message to one or more members in the cluster

Parameters:
destination - Member[] - the destinations, can not be null or zero length, the reason for that is that a membership change can occur and at that time the application is uncertain what group the message actually got sent to.
msg - Serializable - the message to send, has to be serializable, or a ByteMessage to send a pure byte array
options - int - sender options, see class documentation for each interceptor that is configured in order to trigger interceptors
Returns:
a unique Id that identifies the message that is sent
Throws:
ChannelException
See Also:
ByteMessage, SEND_OPTIONS_USE_ACK, SEND_OPTIONS_ASYNCHRONOUS, SEND_OPTIONS_SYNCHRONIZED_ACK

send

UniqueId send(Member[] destination,
              java.io.Serializable msg,
              int options,
              ErrorHandler handler)
              throws ChannelException
Send a message to one or more members in the cluster

Parameters:
destination - Member[] - the destinations, null or zero length means all
msg - ClusterMessage - the message to send
options - int - sender options, see class documentation
handler - ErrorHandler - handle errors through a callback, rather than throw it
Returns:
a unique Id that identifies the message that is sent
Throws:
ChannelException - - if a serialization error happens.

heartbeat

void heartbeat()
Sends a heart beat through the interceptor stacks Use this method to alert interceptors and other components to clean up garbage, timed out messages etc.
If you application has a background thread, then you can save one thread, by configuring your channel to not use an internal heartbeat thread and invoking this method.

See Also:
setHeartbeat(boolean)

setHeartbeat

void setHeartbeat(boolean enable)
Enables or disables internal heartbeat.

Parameters:
enable - boolean - default value is implementation specific
See Also:
heartbeat()

addMembershipListener

void addMembershipListener(MembershipListener listener)
Add a membership listener, will get notified when a new member joins, leaves or crashes
If the membership listener implements the Heartbeat interface the heartbeat() method will be invoked when the heartbeat runs on the channel

Parameters:
listener - MembershipListener
See Also:
MembershipListener

addChannelListener

void addChannelListener(ChannelListener listener)
Add a channel listener, this is a callback object when messages are received
If the channel listener implements the Heartbeat interface the heartbeat() method will be invoked when the heartbeat runs on the channel

Parameters:
listener - ChannelListener
See Also:
ChannelListener, Heartbeat

removeMembershipListener

void removeMembershipListener(MembershipListener listener)
remove a membership listener, listeners are removed based on Object.hashCode and Object.equals

Parameters:
listener - MembershipListener
See Also:
MembershipListener

removeChannelListener

void removeChannelListener(ChannelListener listener)
remove a channel listener, listeners are removed based on Object.hashCode and Object.equals

Parameters:
listener - ChannelListener
See Also:
ChannelListener

hasMembers

boolean hasMembers()
Returns true if there are any members in the group, this call is the same as getMembers().length>0

Returns:
boolean - true if there are any members automatically discovered

getMembers

Member[] getMembers()
Get all current group members

Returns:
all members or empty array, never null

getLocalMember

Member getLocalMember(boolean incAlive)
Return the member that represents this node. This is also the data that gets broadcasted through the membership broadcaster component

Parameters:
incAlive - - optimization, true if you want it to calculate alive time since the membership service started.
Returns:
Member

getMember

Member getMember(Member mbr)
Returns the member from the membership service with complete and recent data. Some implementations might serialize and send membership information along with a message, and instead of sending complete membership details, only send the primary identifier for the member but not the payload or other information. When such message is received the application can retrieve the cached member through this call.
In most cases, this is not necessary.

Parameters:
mbr - Member
Returns:
Member

Apache Tomcat 6.0.39

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