getNumScriptsOnStack

 import java.math.*;

 // Get Number of Scripts (running and max)
 BigDecimal numRunningScripts = new BigDecimal(session.getNumScriptsOnStack());
 BigDecimal maxAllowedScripts = new BigDecimal(session.getMaxScriptsOnStack());

 // Calculate percentage used
 BigDecimal percentageUsedBD = numRunningScripts.divide(maxAllowedScripts, 2, BigDecimal.ROUND_HALF_UP);

 double percentageUsed = percentageUsedBD.doubleValue();

 if (percentageUsed < 90)
 {
     session.log(percentageUsed.toString() + "% of max scripts used");
 }
 else
 {
     session.logWarn("90% max scripts threshold has been reached.");
 }