org.jgroups.blocks

Class 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
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 Log
log
protected String
name
makes the instance unique (together with IDs)
protected RequestHandler
request_handler
The handler for the incoming requests.
protected HashMap
requests
The table of pending requests (keys=Long (request IDs), values=RequestEntry)
protected Scheduler
scheduler
The dispatching thread pool
protected boolean
started
protected Object
transport
The protocol layer to use to pass up/down messages.

Constructor Summary

RequestCorrelator(String name, Object transport, RequestHandler handler)
Constructor.
RequestCorrelator(String name, Object transport, RequestHandler handler, boolean deadlock_detection)
Constructor.
RequestCorrelator(String name, Object transport, RequestHandler handler, boolean deadlock_detection, boolean concurrent_processing)
RequestCorrelator(String name, Object transport, RequestHandler handler, boolean deadlock_detection, Address local_addr)
RequestCorrelator(String name, Object transport, RequestHandler handler, boolean deadlock_detection, Address local_addr, boolean concurrent_processing)
RequestCorrelator(String name, Object transport, RequestHandler handler, 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.
Address
getLocalAddress()
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

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

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.

void
sendRequest(long id, 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
setConcurrentProcessing(boolean concurrent_processing)
void
setDeadlockDetection(boolean flag)
Switch the deadlock detection mechanism on/off
void
setLocalAddress(Address local_addr)
void
setRequestHandler(RequestHandler handler)
void
start()
void
stop()

Field Details

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


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


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 !


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.


local_addr

protected Address local_addr
The address of this group member


log

protected static Log log


name

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


request_handler

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


requests

protected HashMap requests
The table of pending requests (keys=Long (request IDs), values=RequestEntry)


scheduler

protected Scheduler scheduler
The dispatching thread pool


started

protected boolean started


transport

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

Constructor Details

RequestCorrelator

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


RequestCorrelator

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


RequestCorrelator

public RequestCorrelator(String name,
                         Object transport,
                         RequestHandler handler,
                         boolean deadlock_detection,
                         Address local_addr,
                         boolean concurrent_processing)


RequestCorrelator

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

Method Details

done

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


getLocalAddress

public Address getLocalAddress()


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.


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)


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.


sendRequest

public void sendRequest(long id,
                        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.


sendRequest

public void sendRequest(long id,
                        Message msg,
                        RspCollector coll)


setConcurrentProcessing

public void setConcurrentProcessing(boolean concurrent_processing)


setDeadlockDetection

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

Parameters:
flag - the deadlock detection flag


setLocalAddress

public void setLocalAddress(Address local_addr)


setRequestHandler

public void setRequestHandler(RequestHandler handler)


start

public void start()


stop

public void stop()


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