Abstract:
A method and system for routing channels in which messages are transmitted from a source application to a destination application. The system includes a finite-state machine, source message queues, and a source queue manager for managing the source message queues. The source message queues include a transmission queue for holding a first message for subsequent transmission of the first message from the transmission queue over a first channel to a local queue of the destination application. The method includes: activating the finite-state machine; and performing or not performing a channel routing action, by the finite-state machine, depending on: a channel event having caused the first channel to be started or stopped, a channel sender set for the first channel, and an event type characterizing the channel event as normal or abnormal. The channel routing action is a function of the channel event, the channel sender, and the event type.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to the messaging middleware environment wherein messages are transmitted through a transmission network from a source application by means of message queues and relates in particular to a system for defining an alternate channel routing mechanism in such an environment.  
       BACKGROUND  
       [0002]     In a messaging middleware environment such as the MQ series of IBM, applications communicate by means of queues through a transmission network such as a Local Area Network (LAN), a Wide Area Network (WAN) or a Public Switched Telephone Network (PSTN). On the source side, an application program opens a queue and puts messages into it. A mover or Message Channel Agent (MCA) is the program in charge of moving the messages to a target queue located on the destination side.  
         [0003]     When a source application program wants to send a message to a destination application program, it has to communicate with a source queue manager by a Message Queue Interface (MQI) in order to put the message in a transmission queue. Before placing the message in the queue, the queue manager adds a header which contains information from the remote queue definition such as the name of the destination queue manager and the name of the destination queue.  
         [0004]     The transmission of the messages is performed via communication channels. These channels can be started manually or automatically. To start a channel automatically, the transmission queue must be associated with a channel initiation queue into which an initiation message is put when the message to be transmitted is put into the transmission queue. A channel initiator which is an MQ series program is used to monitor the initiation queue. When the channel initiator detects a message in the initiation queue, it starts a Message Channel Agent (MCA) for the particular channel being used and the latter program moves the message over the network to the destination side of the channel.  
         [0005]     On the receiving side, a listener program must have been started. This program monitors a specific port, by default, the port dedicated to MQ series. When the message arrives, the listener starts the MCA associated with the channels which moves the message into a specified local queue. The program that processes the incoming message can be started manually or automatically. To start the program automatically, the MCA puts the incoming message into the local queue and a trigger message into an initiation queue which is monitored by a trigger monitor. The latter program invokes the application specified in the process definition which issues a command to get the message from the local queue.  
         [0006]     In the above system, there may be a communication problem due to a connectivity failure. In such a case, the channel to be used to move the message cannot be initiated and messages are kept in the transmission queue. This may cause an important problem when critical messages whose delivery is guaranteed by the messaging middleware (e.g. database updates, orders, inventories . . . ) are no longer propagated. The only solution to such a problem is to stop the queue manager (thus impacting delivery of the whole business activities) and to manually define an alternate communication path. This is a long, critical and cumbersome process which requires a thorough monitoring of all queue manager intercommunications. Furthermore, this solution results in an important cost since a highly skilled staff must be available and ready to take actions at any time.  
       SUMMARY OF THE INVENTION  
       [0007]     Accordingly, the object of the invention is to provide a system adapted to automatically select an alternate channel to transmit messages between two applications in a messaging middleware environment as soon as the primary channel to be used has failed.  
         [0008]     The invention relates therefore to a routing system for defining an alternate channel routing mechanism in a messaging middleware system wherein messages are transmitted through a transmission network from a source application to a destination application by means of message queues, such a messaging middleware system including a source queue manager for managing the sending of the messages, a transmission queue into which the messages to be transmitted are put by the source application, a primary channel for transmitting messages over the transmission network, a reception queue for receiving the messages and from which they are got by the destination application, a destination queue manager for managing the reception of the messages and an event queue into which the events relating to the primary channel are put. The system comprises a finite-state machine for receiving the channel events as activating inputs and providing actions to be taken for each channel event, one of the actions being to route messages on an alternate channel when the primary channel has failed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The above and other objects, features and advantages of the invention will be better understood by reading the following more particular description of the invention in conjunction with the accompanying drawings wherein:  
         [0010]      FIG. 1  is a block-diagram representing a messaging middleware system wherein a source application program associated with a source queue manager sends messages to a destination application program associated with a destination queue manager;  
         [0011]      FIG. 2  is a schematic representation of a source queue manager including the features according to the invention;  
         [0012]      FIG. 3  is a block-diagram representing the flow of the messages sent from the source queue manager to the destination queue manager and wherein an intermediate queue manager is used; and  
         [0013]      FIG. 4  is a flow chart of the process implemented by the source queue manager each time a channel event is detected. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]     In reference to  FIG. 1 , it is assumed that a source application program  10  wants to communicate messages to a destination application program  12  through a network  14  which can be either a persistent network such as a Local Area Network (LAN), a Wide Area Network (WAN) or a transient network such as a Public Switched Telephone Network (PSTN), or an Integrated Services Digital Network (ISDN).  
         [0015]     On the source side, each message is put (PUT instruction) by the application program and under the control of a source queue manager QMA  16  into a remote queue Q 1   18  before the message is transferred into a transmission queue QMB  20 . The message or the messages of queue  20  are then transmitted from a channel sender (QMA.QMB)  22  to channel receiver (QMA.QMB)  24  on the destination side. Note that, in the following, a channel will designate a logical connection between a channel sender on the source side and a channel receiver on the destination side.  
         [0016]     On the destination side, the messages being received by the channel receiver (QMA.QMB) are queued under the control of a destination queue manager QMB  26  into a local queue Q 1   28 . It must be noted that the remote queue  18  of the source side is not a real queue but it is the definition of the local queue  28  in the destination machine. The messages placed in local queue  28  are then got (GET instruction) by the destination application program under the control of the queue manager QMB  26 .  
         [0017]     The process is the same for the other direction. The messages are put by the destination application program  12  in a remote queue Q 2   30  which is the definition of a local queue Q 2   32  on the source side. The messages transferred in a transmission queue QMA  34  are transmitted through the network  14  from a channel sender (QMB.QMA)  36  to a channel receiver (QMB.QMA)  38 .  
         [0018]     The mechanism according to the invention is schematically illustrated in  FIG. 2 . As already mentioned, the source application program puts a message or several messages into a remote queue  18 . The messages are transferred into a transmission queue  20  under the control of the source queue manager. When one or several messages are been put into transmission queue  20 , an initiating message is put by the remote queue  18  into an initiation queue  40 . A channel initiator  41  continually monitors initiation queue  40  in order to start the message channel agent (MCA)  42  in charge of triggering the transmission messages from the channel sender  22  through network  14 . Note that the queue manager can trigger the starting of MCA, either when a first message is put into the transmission queue, or each time a message is put into the transmission queue or when the queue contains a specified number of messages.  
         [0019]     Assuming that the transmission of the message(s) from the channel sender  22  cannot be established because a failure of the connection between the channel sender and the channel receiver, the mechanism according to the invention avoids the messages to be accumulated in the transmission queue without being transmitted. For this, the program MCA Puts a message in an event queue as soon as it knows the connectivity of the channel to be used. Assuming that MCA detects that this channel has failed, a message “channel stopped” is put into event queue  44  at the same time the transmission of the messages is stopped on the channel.  
         [0020]     The event queue is monitored by a trigger monitor  46  which is in charge of usually monitoring the initiation queue in order to invoke the application program specified in the process  48  and to retrieve the messages received in the local queue. When a channel event message is detected by the trigger monitor  46 , this one invokes a channel routing task  50 , e.g. a daemon, which is waiting for a notification via a GET instruction. This background task then activates a finite-state machine  52  which starts various actions according to the following entries when the primary channel sender is SDR 1  and the alternate channel senders are SDR 2 , SDR 3  and SDR 4   
                                           Channel event   Source   Type   Action                   Channel started   SDR1, SDR2   Normal   None           SDR3 or SDR4       Channel stopped   SDR1   Normal   None       Channel stopped   SDR1   Abnormal   Route primary channel                   (SDR1) to the first                   available alternate                   channel       Channel stopped   SDR2, SDR3   Normal   Restore initial route           or SDR4       (SDR1)       Channel stopped   SDR2, SDR3   Abnormal   Reroute channel           or SDR4       (SDR1) to one of the                   remaining alternate                   channels                  
 
         [0021]     According to the above table giving the actions taken by the finite-state machine  52  in function of the entries, the channel sender and the type, there is no action when the event is “channel started” and the type “normal”. But an action is to be taken as soon as a channel is stopped and the type is abnormal. If the channel being stopped is the primary channel, but the type is abnormal (the channel has failed), the action to be taken is to route channel sender SDR 1  to the first available alternate channel sender such as SDR 2 , SDR 3  or SDR 4 . Note that, when a channel has failed, it may be due to the failure of the link, of the channel sender, of the channel receiver, or a combination of these ones.  
         [0022]     In reference to  FIG. 3 , it is assumed that a channel has failed and the primary channel sender SDR 1  is unavailable. In such a case, in QM 1   60 , the transmission queue  62  receiving the messages from remote queue  64  does not send any longer the messages by using SDR 1 . Assuming that, in the destination queue manager QM 2   66 , the primary channel receiver RCVR 1  is always available, the messages are sent on the channel defined by the pair SDR 2  and RCVR 1  instead of the pair SDR 1  and RCVR 1 . But, the messages being received are always put into the same local or transmission queue  68 .  
         [0023]     Assuming that, not only the primary channel sender SDR 1  is unavailable, but also the primary channel receiver RCVR 2  is available, it is possible to use a different pair of channel sender and channel receiver such as the pair SDR 3  and RCVR 2  to send the messages over network  14 . Nevertheless, the messages received in QM 2  are put in the same local or transmission queue  68 .  
         [0024]     In an alternate embodiment illustrated in  FIG. 3 . the transmission of messages from QM 1  to QM 2  is performed by using an intermediate queue manager QM 3   70 . In such a case, the messages queued in the transmission queue  62  of QM 1  are sent from the channel sender SDR 4  through network  14  to the channel receiver RCVR 3  of QM 3 . The received messages are put into the local or transmission queue  72 . Then, they are transferred into the remote queue  74  before being put into the transmission queue  72 . It must be noted that the remote queue  74  is not a real queue but a structure which contains the characteristics of the local or transmission queue  68  in QM 2 . Therefore, the messages which are transferred from remote queue  74  to transmission queue  72  in QM 2  are formatted to be forwarded to QM 2 . As illustrated in  FIG. 3 , the messages are sent from the channel sender SDR 5  through network  14  to the channel receiver RCVR 2  of QM 2 .  
         [0025]     The flow chart corresponding to the steps carried out by the source queue manager when a channel event has been posted is illustrated in  FIG. 4 . First, the channel routing task  50  (see  FIG. 2 ) which is a daemon in the preferred embodiment, is triggered by the channel event put in the event queue (step  76 ). It is determined whether the channel being identified by the event is a channel being monitored by the system (step  78 ). If not, the process is looped back to the beginning. If it is the case, it is determined whether the channel event is a “channel stopped” (step  80 ). If not, the process is looped back to the beginning. If it is the case, it is determined whether the channel which is stopped is a primary channel or not (step  82 ). If so, it is determined whether there is an alternate channel being available to replace the primary channel (step  84 ). If not, the process is looped back to the beginning.  
         [0026]     If there is an alternate channel which may be used, for example SDR 2 , SDR 3  or SDR 4 , the transmission queue name of the selected alternate channel is updated with the transmission queue name of the primary channel. Then, the message sequence number for the channel is reset with a specified sequence number to be used the next time that the channel is started (step  88 ). In addition to resetting the value at the end at which the command is issued, the value at the other end will also be reset to the same value, next time this channel is initiated. The next step consists in disabling the transmission queue triggering and inhibiting the GET operations on related transmission queue (step  90 ). The data of related process is then updated with the alternate channel name e.g., SDR 2  (step  92 ). Finally, the GET operations on the transmission queue are re-enabled and the triggering of the related transmission queue is enabled (step  94 ), before looping back the process to the beginning.  
         [0027]     When it is determined that the channel being stopped is not the primary channel (step  82 ), this means that the channel being stopped is already an alternate channel. In such a case, the transmission queue triggering is disabled and the GET operation are inhibited (step  96 ) before updating the data of the related process with the original primary channel name in order to recover the initial configuration (step  98 ). Then, the message sequence number is reset as in the case when the primary channel has failed (step  100 ). As previously, the next step consists in enabling the GET operations and enabling the triggering of the transmission queue (step  102 ). Then, the transmission queue name of the alternate channel is cleared in order to remove the logical communication link used for the alternate routing (step  104 ) before looping back to the beginning of the process.