org.jgroups.blocks
Class RequestCorrelator

java.lang.Object
  extended byorg.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 call_stack
          This field is used only if deadlock detection is enabled.
protected  org.jgroups.blocks.RequestCorrelator.CallStackSetter call_stack_setter
          This field is used only if deadlock detection is enabled.
protected  boolean deadlock_detection
          Whether to perform deadlock detection is synchronous calls
protected  Address local_addr
          The address of this group member
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.HashMap requests
          The table of pending requests (keys=Long (request IDs), values=RequestEntry)
protected  Scheduler scheduler
          The dispatching thread pool
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)
           
 
Method Summary
 void done(long id)
          Used to signal that a certain request may be garbage collected as all responses have been received.
 void finalize()
          Stop the dispatch thread pool
 void 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 sendRequest(long id, java.util.List dest_mbrs, Message msg, RspCollector coll)
          Send a request to a group.
 void sendRequest(long id, Message msg, RspCollector coll)
          Helper method for sendRequest(long,List,Message,RspCollector).
 void setDeadlockDetection(boolean flag)
          Switch the deadlock detection mechanism on/off
 void setLocalAddress(Address local_addr)
           
 void setRequestHandler(RequestHandler handler)
          ???
 void start()
           
 void stop()
           
 
Methods inherited from class java.lang.Object
clone, equals, 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 java.util.HashMap 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


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 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 to perform deadlock detection is synchronous calls


call_stack_setter

protected org.jgroups.blocks.RequestCorrelator.CallStackSetter call_stack_setter
This field is used only if deadlock detection is enabled. It sets the calling stack for to that for the currently running request

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 (passUp()/passDown() 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 (passUp()/passDown() 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,
                         Address local_addr)
Method Detail

finalize

public void finalize()
Stop the dispatch thread pool


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)
???


sendRequest

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


sendRequest

public void sendRequest(long id,
                        java.util.List dest_mbrs,
                        Message msg,
                        RspCollector coll)
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.

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 void 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.


start

public void start()

stop

public void stop()

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 event should be forwarded further up, otherwise false (message was consumed)

setLocalAddress

public void setLocalAddress(Address local_addr)


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