Difference between revisions of "Doc:latest/evalguide/csa112"

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==csa212 Event Subscription==
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==csa112 Event Subscription==
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An event service is an communications mechanism organised around the categories of data rather then senders and receivers.  A "publisher" posts a message to a well-known event channel and all "subscribers" receive the message.  Publishers and subscribers do not need to know who each other are; they need only know the event channel name. 
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As the Messaging service is similar to mail, the Event service is similar to a bulletin board.
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===Objective===
 
===Objective===
  
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The objective of csa212 is to learn how to use Clovis' event service to subscribe to events and to extract the relevant information from the events received by subscription.
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The objective of csa112 is to learn how to use the SAFplus Platform event service to subscribe to events and to extract the relevant information from the events received by subscription.
  
 
===What you will learn===
 
===What you will learn===
  
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You will learn  
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You will learn:
 
*how to initialize the event library
 
*how to initialize the event library
 
*how to subscribe to events
 
*how to subscribe to events
 
*how to receive events
 
*how to receive events
 
*how to extract the event data
 
*how to extract the event data
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The SAFplus Event service is SA-Forum compliant and this tutorial expects that you will refer to the relevant SA-Forum document for an in-depth description of the APIs used.
  
 
===Code===
 
===Code===

Revision as of 22:12, 21 January 2013

Contents

csa112 Event Subscription

An event service is an communications mechanism organised around the categories of data rather then senders and receivers. A "publisher" posts a message to a well-known event channel and all "subscribers" receive the message. Publishers and subscribers do not need to know who each other are; they need only know the event channel name.

As the Messaging service is similar to mail, the Event service is similar to a bulletin board.


Objective

The objective of csa112 is to learn how to use the SAFplus Platform event service to subscribe to events and to extract the relevant information from the events received by subscription.

What you will learn

You will learn:

  • how to initialize the event library
  • how to subscribe to events
  • how to receive events
  • how to extract the event data

The SAFplus Event service is SA-Forum compliant and this tutorial expects that you will refer to the relevant SA-Forum document for an in-depth description of the APIs used.

Code

One difference to note between this application and previous ones is that this application will not have a main loop in clCompAppInitialize. Instead we will do our work in callback code. This means that when we return from clCompAppInitialize we won't exit the application.

clCompAppMain.c 
    SaNameT    evtChannelName = {
                    sizeof EVENT_CHANNEL_NAME - 1,
                    EVENT_CHANNEL_NAME
           };

    SaEvtChannelHandleT    evtChannelHandle = 0;
    SaEvtHandleT      evtHandle = CL_HANDLE_INVALID_VALUE;

    static void
    csa212Comp_appEventCallback( SaEvtSubscriptionIdT subscriptionId,
                                          SaEvtEventHandleT eventHandle,
                                          SaSizeT eventDataSize);

Here we define variables to hold the payload of our event. Note the initialization of the evtChannelName. The length is set to the length of the EVENT_CHANNEL_NAME string WITHOUT including the null terminator.

clCompAppMain.c 
    ClRcT
    clCompAppInitialize(ClUint32T argc,ClCharT *argv[])
    {
        ....

        const SaEvtCallbacksT   evtCallbacks = {
                           NULL,
                           csa212Comp_appEventCallback
                        };

        ...

        // publish our event callbacks
        rc = saEvtInitialize(&evtHandle, &evtCallbacks, &evtVersion);

        ...

We initialize the OpenClovis Event Manager with clEventInitialize. We pass the address of the variable where we want the event handle stored. We pass the address of our event callback functions structure. Note that the only event callback function that we specify is csa112Comp_appEventCallback. We do not specify the other callback which is the Asynchronous channel open callback. We specify NULL for that field of evtCallbacks because we don't open our event channel asynchronously.:

clCompAppMain.c 
    ClRcT
    clCompAppInitialize(ClUint32T argc, ClCharT *argv[])
    {

        ....

        // Open an event chanel so that we can subscribe to events on that channel
        rc = saEvtChannelOpen(evtHandle,
                &evtChannelName,
                (SA_EVT_CHANNEL_SUBSCRIBER |
                 SA_EVENT_CHANNEL_CREATE),
                (SaTimeT)SA_TIME_END,
                &evtChannelHandle);
        if (rc != SA_AIS_OK)
        {   
            clprintf(CL_LOG_SEV_ERROR, "%s\t:Failure opening event channel[0x%x] at %ld\n", appname,

            logrc(CL_LOG_ERROR, "%s\t:Failure opening event channel[0x%x]\n",
                    appname, rc
            goto errorexit;
        }

        rc = saEvtEventSubscribe(evtChannelHandle, NULL, 1);
        if (rc != CL_OK)
        {
            clprintf(CL_LOG_SEV_ERROR, "%s\t: Failed to subscribe to event channel [0x%x]\n",
                    appname, rc);
            logrc(CL_LOG_ERROR,
                    "%s\t:Failed to subscribe to event channel [0x%x]\n",
                    appname, rc);
            goto errorexit;
        }

Within the above code we open the channel synchronously. We pass the handle we got back from clEventInitialize, the channel name we defined previously, flags that indicate this process is subscribing to the channel and it's a global channel, and that the channel should be created if it's not already there, a timeout value of "forever", and the address of the location where the channel handle should be stored. Then, we subscribe to a specific event stream on the event channel. The EVENT_TYPE constant is defined in common/common.h as 5432. This value is used by the event publisher when it sends events. The constant 1 being passed simply identifies this specific subscription on this channel. This value will be passed to our event delivery callback function.

clCompAppMain.c 
    static void
    csa212Comp_appEventCallback( SaEvtSubscriptionIdT subscriptionId,
                                              SaEvtEventHandleT eventHandle,
                                              SaSizeT eventDataSize)
    {
        SaAisErrorT  rc = SA_AIS_OK;

        ClPtrT  resTest = NULL;
        ClSizeT resSize;
        if (running == 0 || ha_state != SA_AMF_HA_ACTIVE)
        {
           return; 
        }
        clprintf(CL_LOG_SEV_INFO,"We've got an event to receive");

        resTest = clHeapAllocate(eventDataSize + 1);
        if (resTest == NULL)
        {
            logmsg(CL_LOG_ERROR, "%s\tFailed to allocate space for event\n, appname");
            return; 
        }
        *(((char *)resTest) + eventDataSize) = 0;
        resSize = eventDataSize;
        rc = saEvtEventDataGet(eventHandle, resTest, &resSize);
        if (rc != SA_AIS_OK)
        {
           logrc(CL_LOG_ERROR, "%s\t:Failed to get event data [0x%x]\n",
                    appname, rc);
        }

        clprintf(CL_LOG_SEV_INFO,"received event: %s\n", (char *)resTest);
        return;

    }

The event delivery callback function is named csa112Comp_appEventCallback. First it checks that the running variable is not zero and that the High Availability State is CL_AMS_HA_STATE_ACTIVE, otherwise it returns, dropping the event in the bit bucket. Next it checks whether our incoming data buffer needs to be deallocated. If there is a buffer, it deallocates it and then allocates enough data to receive the incoming event data. Then, we extract the data from the event into the newly allocated buffer using clEventDataGet. Finally, we print the event data we received using clprintf which is another member of Clovis' OS Abstraction Layer. As its name and usage suggest, it is the OSAL replacement for printf.

csa212 SA Forum Compliant Event Subscription

csa212 demonstrates the usage of SA Forum's Event Service. This sample application does not deviate functionally from csa112. The differences in code are due to using SA Forum data types (structures) and APIs , as presented in the following two tables. (Note we have not repeated data types and APIs covered previously.)

SA Forum Data Types with the SAFplus Platform equivalent
SA Forum Data Types OpenClovis Data Types
SaEvtHandleT ClEventInitHandleT
SaEvtChannelHandleT ClEventChannelHandleT
SaEvtCallbacksT ClEventCallbacksT
SA_EVT_CHANNEL_SUBSCRIBER CL_EVENT_CHANNEL_SUBSCRIBER
SA_EVT_CHANNEL_CREATE CL_EVENT_CHANNEL_CREATE
SA_TIME_END CL_RMD_TIMEOUT_FOREVER



SA Forum APIs with the SAFplus Platform equivalent
SA Forum APIs OpenClovis APIs
SaEvtInitialize ClEventInitialize
saEvtChannelOpen clEventChannelOpen
saEvtEventSubscribe clEventExtSubscribe
saEvtEventDataGet clEventDataGet
saEvtChannelClose clEventChannelClose
saEvtFinalize clEventFinalize

How to Run csa212 and What to Observe

  1. Start example csa212 in the same manner that we have started previous examples, with the SAFplus Platform Console.(Unlock csa212SGI0 instead of csa112SGI0 to run csa212). 
     # cd /root/asp/bin
 # ./asp_console


cli[Test]-> setc 1
cli[Test:SCNodeI0]-> setc cpm
cli[Test:SCNodeI0:CPM]-> amsLockAssignment sg csa212SGI0

    Looking at the log file for this example you should see the following.

    /root/asp/var/log/csa212CompI3Log.latest 
      Fri Oct  1 13:14:16.935 2010 (PayloadNodeI1.10366 : csa212CompEO.---.---.00001 :   INFO) Component [csa212CompI3] : PID [10366]. Initializing

  Fri Oct  1 13:14:16.935 2010 (PayloadNodeI1.10366 : csa212CompEO.---.---.00002 :   INFO)    IOC Address             : 0x4

  Fri Oct  1 13:14:16.935 2010 (PayloadNodeI1.10366 : csa212CompEO.---.---.00003 :   INFO)    IOC Port                : 0x80

  Fri Oct  1 13:15:31.389 2010 (PayloadNodeI1.10366 : csa212CompEO.---.---.00004 :   INFO) Component [csa212CompI3] : PID [10366]. CSI Set Received
  2. Now unlock the application with: 
    cli[Test:SCNodeI0:CPM]-> amsUnlock sg csa212SGI0

    At this point you should see the following in the log.

    /root/asp/var/log/csa212CompI3Log.latest 
     Fri Oct  1 13:15:31.389 2010 (PayloadNodeI1.10366 : csa212CompEO.---.---.00012 :   INFO) csa212: ACTIVE state requested; activating service

    Thats all there is to this example. What you are looking at in the log is the output of our event listener. It doesn't appear very interesting because we have not yet written an event publisher that will give the program something to output. We'll do that in the next example (csa213).

  3. At this point we can shut down our example in the usual fashion. 
    cli[Test:SCNodeI0:CPM]-> amsLockAssignment sg csa212SGI0
cli[Test:SCNodeI0:CPM]-> amsLockInstantiation sg csa212SGI0
cli[Test:SCNodeI0:CPM]-> end
cli[Test:SCNodeI0]-> end
cli[Test]-> bye

OpenClovis Note.pngWhen running model csa212 you will not see the output described for the the amsLockAssignment and amsUnlock commands.

Summary and References

We've seen how to create a basic event subscriber application using Clovis' event manager library. For further reading check the Clovis SAFplus Platform API reference guide, specifically the section on the event manager. Also, the header file: clEventExtApi.h should be helpful.

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