Package 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

    • 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,
                        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