Periodic Scriptlet

This example shows how to implement a process which is executed periodically based on the scriptlet processor gsn.processor.ScriptletProcessor. Thanks to the script, we can detect a data source which fails at producing data by periodically checking the time between the last StreamElement produced and the current time.

Virtual Sensor Description File

This virtual sensor gets its data from the MemoryMonitorVS and logs a warning message, when the last StreamElement inserted was more 10 seconds ago.

<virtual-sensor name="PeriodicScriptlet" priority="10">
    <processing-class>
        <class-name>gsn.processor.ScriptletProcessor</class-name>
        <init-params>
            <param name="persistant">true</param>
            <param name="scriptlet">
                <![CDATA[
                    // This script is executed every time we process a new StreamElement.
                    // We update the 'lastProcessedTime' variable.
                    lastProcessedTime = System.currentTimeMillis();
                ]]>
            </param>
            <param name="period">5000</param>
            <param name="scriplet-periodic">
                <![CDATA[
                    // This script is periodically executed, every 5 seconds (5000 ms set in the parameter above).
                    // We check the time difference between the current time and the last time a StreamElementhas been
                    // processed. If the time difference is greater than an offset (10000 ms set in the parameter below),
                    // we log a warning message.
                    
                    def timeDifferenceOffset = 10000;   // 10 sec

                    def currentTime = System.currentTimeMillis();

                    if ( ! isdef('lastProcessedTime')) {
                        lastProcessedTime = currentTime;
                    }
                    else {
                        def timeDifference = currentTime - lastProcessedTime;
                        if (timeDifference > timeDifferenceOffset) {
                            println 'Warning! No StreamElement have been processed for the last ' + timeDifference + ' ms.';
                        }
                        else {
                            println 'Ok! The last StreamElement has been processed ' + timeDifference + ' ms ago.';
                        }
                    }
                ]]>
            </param>
        </init-params>
        <output-structure>
            <field name="HEAP" type="double"/>
            <field name="NON_HEAP" type="double"/>
            <field name="PENDING_FINALIZATION_COUNT" type="double"/>
        </output-structure>
    </processing-class>
    <description>
        This Virtual Sensor demonstrates the use of the scriplet processor (gsn.processor.ScriptletProcessor) for detecting
        a data source which fails at producing data. It gets its data from the MemoryMonitorVS.
    </description>
    <addressing/>
    <storage history-size="1"/>
    <streams>
        <stream name="stream1">
            <source alias="source1" storage-size="1" sampling-rate="1">
                <address wrapper="local">
                    <predicate key="name">MemoryMonitorVS</predicate>
                </address>
                <query>select * from wrapper</query>
            </source>
            <query>select * from source1</query>
        </stream>
    </streams>
</virtual-sensor>