org.jgroups.blocks
Class RequestCorrelator

java.lang.Object
  extended by org.jgroups.blocks.RequestCorrelator

public class RequestCorrelator
extends java.lang.Object

Framework to send requests and receive matching responses (matching on request ID). Multiple requests can be sent at a time. Whenever a response is received, the correct RspCollector is looked up (key = id) and its method receiveResponse() invoked. A caller may use done() to signal that no more responses are expected, and that the corresponding entry may be removed.

RequestCorrelator can be installed at both client and server sides, it can also switch roles dynamically; i.e., send a request and at the same time process an incoming request (when local delivery is enabled, this is actually the default).

Author:
Bela Ban

Nested Class Summary
static class RequestCorrelator.Header
          The header for RequestCorrelator messages
 
Field Summary
protected  java.util.Stack<Address> call_stack
          This field is used only if deadlock detection is enabled.
protected  boolean concurrent_processing
          Process items on the queue concurrently (Scheduler).
protected  boolean deadlock_detection
          Whether or not to perform deadlock detection for synchronous (potentially recursive) group method invocations.
protected  Address local_addr
          The address of this group member
protected static org.apache.commons.logging.Log log
           
protected  RpcDispatcher.Marshaller2 marshaller
          Possibility for an external marshaller to marshal/unmarshal responses
protected  java.lang.String name
          makes the instance unique (together with IDs)
protected  RequestHandler request_handler
          The handler for the incoming requests.
protected  java.util.concurrent.ConcurrentMap<java.lang.Long,RspCollector> requests
          The table of pending requests (keys=Long (request IDs), values=RequestEntry)
protected  Scheduler scheduler
          The dispatching thread pool
protected  boolean started
           
protected  java.lang.Object transport
          The protocol layer to use to pass up/down messages.
 
Constructor Summary
RequestCorrelator(java.lang.String name, java.lang.Object transport, RequestHandler handler)
          Constructor.
RequestCorrelator(java.lang.String name, java.lang.Object transport, RequestHandler handler, Address local_addr)
           
RequestCorrelator(java.lang.String name, java.lang.Object transport, RequestHandler handler, boolean deadlock_detection)
          Constructor.
RequestCorrelator(java.lang.String name, java.lang.Object transport, RequestHandler handler, boolean deadlock_detection, Address local_addr)
           
RequestCorrelator(java.lang.String name, java.lang.Object transport, RequestHandler handler, boolean deadlock_detection, Address local_addr, boolean concurrent_processing)
           
RequestCorrelator(java.lang.String name, java.lang.Object transport, RequestHandler handler, boolean deadlock_detection, boolean concurrent_processing)
           
 
Method Summary
 void done(long id)
          Used to signal that a certain request may be garbage collected as all responses have been received.
 Address getLocalAddress()
           
 RpcDispatcher.Marshaller getMarshaller()
           
protected  void handleRequest(Message req, RequestCorrelator.Header hdr)
          Handle a request msg for this correlator
 boolean receive(Event evt)
          Callback.
 boolean receiveMessage(Message msg)
          Handles a message coming from a layer below
 void receiveSuspect(Address mbr)
          Event.SUSPECT event received from a layer below.
 void receiveView(View new_view)
          Event.VIEW_CHANGE event received from a layer below.
 void registerProbeHandler(TP transport)
           
 void sendRequest(long id, java.util.List<Address> dest_mbrs, Message msg, RspCollector coll)
           
 void sendRequest(long id, java.util.List<Address> dest_mbrs, Message msg, RspCollector coll, boolean use_anycasting)
          Send a request to a group.
 void sendRequest(long id, Message msg, RspCollector coll)
          Helper method for sendRequest(long,List,Message,RspCollector).
 void setConcurrentProcessing(boolean concurrent_processing)
           
 void setDeadlockDetection(boolean flag)
          Switch the deadlock detection mechanism on/off
 void setLocalAddress(Address local_addr)
           
 void setMarshaller(RpcDispatcher.Marshaller marshaller)
           
 void setRequestHandler(RequestHandler handler)
           
 void start()
           
 void stop()
           
 void unregisterProbeHandler(TP transport)
           
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

transport

protected java.lang.Object transport
The protocol layer to use to pass up/down messages. Can be either a Protocol or a Transport


requests

protected final java.util.concurrent.ConcurrentMap<java.lang.Long,RspCollector> requests
The table of pending requests (keys=Long (request IDs), values=RequestEntry)


request_handler

protected RequestHandler request_handler
The handler for the incoming requests. It is called from inside the dispatcher thread


marshaller

protected RpcDispatcher.Marshaller2 marshaller
Possibility for an external marshaller to marshal/unmarshal responses


name

protected java.lang.String name
makes the instance unique (together with IDs)


scheduler

protected Scheduler scheduler
The dispatching thread pool


local_addr

protected Address local_addr
The address of this group member


call_stack

protected java.util.Stack<Address> call_stack
This field is used only if deadlock detection is enabled. In case of nested synchronous requests, it holds a list of the addreses of the senders with the address at the bottom being the address of the first caller


deadlock_detection

protected boolean deadlock_detection
Whether or not to perform deadlock detection for synchronous (potentially recursive) group method invocations. If on, we use a scheduler (handling a priority queue), otherwise we don't and call handleRequest() directly.


concurrent_processing

protected boolean concurrent_processing
Process items on the queue concurrently (Scheduler). The default is to wait until the processing of an item has completed before fetching the next item from the queue. Note that setting this to true may destroy the properties of a protocol stack, e.g total or causal order may not be guaranteed. Set this to true only if you know what you're doing !


started

protected boolean started

log

protected static final org.apache.commons.logging.Log log
Constructor Detail

RequestCorrelator

public RequestCorrelator(java.lang.String name,
                         java.lang.Object transport,
                         RequestHandler handler)
Constructor. Uses transport to send messages. If handler is not null, all incoming requests will be dispatched to it (via handle(Message)).

Parameters:
name - Used to differentiate between different RequestCorrelators (e.g. in different protocol layers). Has to be unique if multiple request correlators are used.
transport - Used to send/pass up requests. Can be either a Transport (only send() will be used then), or a Protocol (up_prot.up()/down_prot.down() will be used)
handler - Request handler. Method handle(Message) will be called when a request is received.

RequestCorrelator

public RequestCorrelator(java.lang.String name,
                         java.lang.Object transport,
                         RequestHandler handler,
                         Address local_addr)

RequestCorrelator

public RequestCorrelator(java.lang.String name,
                         java.lang.Object transport,
                         RequestHandler handler,
                         boolean deadlock_detection)
Constructor. Uses transport to send messages. If handler is not null, all incoming requests will be dispatched to it (via handle(Message)).

Parameters:
name - Used to differentiate between different RequestCorrelators (e.g. in different protocol layers). Has to be unique if multiple request correlators are used.
transport - Used to send/pass up requests. Can be either a Transport (only send() will be used then), or a Protocol (up_prot.up()/down_prot.down() will be used)
handler - Request handler. Method handle(Message) will be called when a request is received.
deadlock_detection - When enabled (true) recursive synchronous message calls will be detected and processed with higher priority in order to solve deadlocks. Slows down processing a little bit when enabled due to runtime checks involved.

RequestCorrelator

public RequestCorrelator(java.lang.String name,
                         java.lang.Object transport,
                         RequestHandler handler,
                         boolean deadlock_detection,
                         boolean concurrent_processing)

RequestCorrelator

public RequestCorrelator(java.lang.String name,
                         java.lang.Object transport,
                         RequestHandler handler,
                         boolean deadlock_detection,
                         Address local_addr)

RequestCorrelator

public RequestCorrelator(java.lang.String name,
                         java.lang.Object transport,
                         RequestHandler handler,
                         boolean deadlock_detection,
                         Address local_addr,
                         boolean concurrent_processing)
Method Detail

setDeadlockDetection

public void setDeadlockDetection(boolean flag)
Switch the deadlock detection mechanism on/off

Parameters:
flag - the deadlock detection flag

setRequestHandler

public void setRequestHandler(RequestHandler handler)

setConcurrentProcessing

public void setConcurrentProcessing(boolean concurrent_processing)

sendRequest

public void sendRequest(long id,
                        Message msg,
                        RspCollector coll)
                 throws java.lang.Exception
Helper method for sendRequest(long,List,Message,RspCollector).

Throws:
java.lang.Exception

getMarshaller

public RpcDispatcher.Marshaller getMarshaller()

setMarshaller

public void setMarshaller(RpcDispatcher.Marshaller marshaller)

sendRequest

public void sendRequest(long id,
                        java.util.List<Address> dest_mbrs,
                        Message msg,
                        RspCollector coll)
                 throws java.lang.Exception
Throws:
java.lang.Exception

sendRequest

public void sendRequest(long id,
                        java.util.List<Address> dest_mbrs,
                        Message msg,
                        RspCollector coll,
                        boolean use_anycasting)
                 throws java.lang.Exception
Send a request to a group. If no response collector is given, no responses are expected (making the call asynchronous).

Parameters:
id - The request ID. Must be unique for this JVM (e.g. current time in millisecs)
dest_mbrs - The list of members who should receive the call. Usually a group RPC is sent via multicast, but a receiver drops the request if its own address is not in this list. Will not be used if it is null.
msg - The request to be sent. The body of the message carries the request data
coll - A response collector (usually the object that invokes this method). Its methods receiveResponse() and suspect() will be invoked when a message has been received or a member is suspected, respectively.
Throws:
java.lang.Exception

done

public void done(long id)
Used to signal that a certain request may be garbage collected as all responses have been received.


receive

public boolean receive(Event evt)
Callback.

Called by the protocol below when a message has been received. The algorithm should test whether the message is destined for us and, if not, pass it up to the next layer. Otherwise, it should remove the header and check whether the message is a request or response. In the first case, the message will be delivered to the request handler registered (calling its handle() method), in the second case, the corresponding response collector is looked up and the message delivered.

Parameters:
evt - The event to be received
Returns:
Whether or not the event was consumed. If true, don't pass message up, else pass it up

start

public final void start()

stop

public void stop()

registerProbeHandler

public void registerProbeHandler(TP transport)

unregisterProbeHandler

public void unregisterProbeHandler(TP transport)

receiveSuspect

public void receiveSuspect(Address mbr)
Event.SUSPECT event received from a layer below.

All response collectors currently registered will be notified that mbr may have crashed, so they won't wait for its response.


receiveView

public void receiveView(View new_view)
Event.VIEW_CHANGE event received from a layer below.

Mark all responses from members that are not in new_view as NOT_RECEIVED.


receiveMessage

public boolean receiveMessage(Message msg)
Handles a message coming from a layer below

Returns:
true if the message was consumed, don't pass it further up, else false

getLocalAddress

public Address getLocalAddress()

setLocalAddress

public void setLocalAddress(Address local_addr)

handleRequest

protected void handleRequest(Message req,
                             RequestCorrelator.Header hdr)
Handle a request msg for this correlator

Parameters:
req - the request msg


Copyright © 1998-2008 Bela Ban. All Rights Reserved.