{ Make this readable }

Wednesday, October 31, 2007

Loose metal-strap watch: DIY

Have you ever bought a metal-strap watch and found the strap to be too loose? Well, loose but not so loose that removing another link in the strap would solve it?

I had this problem recently and my new watch kept slipping down my wrist all the time. I couldn't remove any more links because it would make it very tight. So, I added a strip of "Mounting tape" to the inner side of the clasp - the part of the strap that touches the underside of the wrist and - problem solved! Just wait for the glue on the double side sticky tape to dry though.

And, I found those plastic topped push-pins to be very useful while removing those links. All you need a mallet or something similar to force the link-pins out. Here's some info - How to.

Sunday, October 21, 2007

Radio - Classic Rock

If you are a Classic Rock fan, you'll love this Station - KFRC. Of course, if you live in the Bay Area you probably already know - 106.9 FM. You can even listen online for free. I absolutely love the songs they play. Now I don't have to spend a small fortune on CDs.

Saturday, October 20, 2007

ClassLoader (ab)use

A weird piece of code it was and I had the misfortune of having to get around this very piece of code - a hand me down, from an old version of the product.

It was some kind of a store/map where the keys were Classes instead of Strings as keys, which you would've seen in most "regular" Maps. So, it automatically limited the range of keys one could use. New Classes had to be created and compiled and then used as keys, if required. I had to use this package because there a lot of business logic tied to this store and it couldn't be modified. There were a lot of versions that were already in production.

I needed to use the very same store but my keys were going to be dynamic. The only choices I had was to either compile new classes beforehand or generate new Classes on the fly in the JVM using BCEL or ASM or any of those scary Bytecode libraries. That was when I realized that there was a simpler solution. One that didn't really need an over-the-top solution. I chose to use (rather abuse) ClassLoaders.

I realized that I didn't really need the Key-Classes anywhere other than to store data into the map. So, I created an empty Class and then every time I needed a new Key-Class I would just load my fixed Class from a new ClassLoader. Since the same Class can be loaded into the JVM by multiple ClassLoaders, the Store/map would have no idea that they were all the same Classes but from different ClassLoaders. So, I created a small custom ClassLoader that would do this everytime a new Key was required.

I must mention that I was allowed to sub-Class this store.


This is what the "weird" old Store looks like:


public class AbsurdLegacyStore {
protected final Map<Class, Set<Object>> perTypeStore;

public AbsurdLegacyStore() {
this.perTypeStore = new HashMap<Class, Set<Object>>();
}

public Map<Class, Set<Object>> getPerTypeStore() {
return perTypeStore;
}

public void addToStoreAndDoWork(Employee e) {
Set<Object> set = perTypeStore.get(Employee.class);
if (set == null) {
set = new HashSet<Object>();
perTypeStore.put(Employee.class, set);
}

set.add(e);
}

public void addToStoreAndDoWork(Customer c) {
Set<Object> set = perTypeStore.get(Customer.class);
if (set == null) {
set = new HashSet<Object>();
perTypeStore.put(Customer.class, set);
}

set.add(c);
}

public void addToStoreAndDoWork(Supplier s) {
Set<Object> set = perTypeStore.get(Supplier.class);
if (set == null) {
set = new HashSet<Object>();
perTypeStore.put(Supplier.class, set);
}

set.add(s);
}
}


All the fixed key Classes:


public class Customer {
protected final String name;

public Customer(String name) {
this.name = name;
}

public String getName() {
return name;
}

@Override
public String toString() {
return name;
}
}



public class Employee {
protected final String name;

public Employee(String name) {
this.name = name;
}

public String getName() {
return name;
}

@Override
public String toString() {
return name;
}
}



public class Supplier {
protected final String name;

public Supplier(String name) {
this.name = name;
}

public String getName() {
return name;
}

@Override
public String toString() {
return name;
}
}



public class ChannelPartner {
protected final String name;

public ChannelPartner(String name) {
this.name = name;
}

@Override
public String toString() {
return name;
}
}


The "hacky" sub-Class of the old Store with its own custom ClassLoader:


public class HackyTypeBasedStore extends AbsurdLegacyStore {
protected Map<String, Class> dynamicSalesRegionTypes;

public HackyTypeBasedStoere() {
this.dynamicSalesRegionTypes = new HashMap<String, Class>();
}

public void registerNewSalesRegion(String salesRegionName) throws ClassNotFoundException {
if (dynamicSalesRegionTypes.containsKey(salesRegionName)) {
return;
}

ClassLoader customLoader = new CustomClassLoader();
Class dynamicType = customLoader.loadClass(SalesRegion.class.getName());
dynamicSalesRegionTypes.put(salesRegionName, dynamicType);
}

public void addToStoreAndDoWork(String salesRegionName, ChannelPartner partner) {
Class regionType = dynamicSalesRegionTypes.get(salesRegionName);

Set<Object> set = perTypeStore.get(regionType);
if (set == null) {
set = new HashSet<Object>();
perTypeStore.put(regionType, set);
}

set.add(partner);
}

public static void main(String[] args) throws ClassNotFoundException {
HackyTypeBasedStore store = new HackyTypeBasedStore();

String salesRegion1 = "Europe";
String salesRegion2 = "Americas";
String salesRegion3 = "Asia";

store.registerNewSalesRegion(salesRegion1);
store.registerNewSalesRegion(salesRegion2);
store.registerNewSalesRegion(salesRegion3);

ChannelPartner partnerABCD = new ChannelPartner("ABCD");
store.addToStoreAndDoWork(salesRegion1, partnerABCD);
store.addToStoreAndDoWork(salesRegion3, partnerABCD);

ChannelPartner partnerKLMN = new ChannelPartner("KLMN");
store.addToStoreAndDoWork(salesRegion2, partnerKLMN);
store.addToStoreAndDoWork(salesRegion3, partnerKLMN);

ChannelPartner partnerWXYZ = new ChannelPartner("WXYZ");
store.addToStoreAndDoWork(salesRegion2, partnerWXYZ);

// --------

Customer customer = new Customer("Customer-A");
store.addToStoreAndDoWork(customer);

Employee employee = new Employee("Employee-1");
store.addToStoreAndDoWork(employee);

Supplier supplier5 = new Supplier("Supplier-5");
store.addToStoreAndDoWork(supplier5);

Supplier supplier6 = new Supplier("Supplier-6");
store.addToStoreAndDoWork(supplier6);

// ---------

Map<Class, Set<Object>> wickedMap = store.getPerTypeStore();
for (Class key : wickedMap.keySet()) {
Set<Object> set = wickedMap.get(key);

System.out.println("Key: " + key.getName() + ", ClassLoader: " + key.getClassLoader());
System.out.println("Data: " + set);
System.out.println();
}
}

// --------

public static class CustomClassLoader extends URLClassLoader {
protected final String nameAsPath;

public CustomClassLoader() {
super(new URL[0]);

String name = SalesRegion.class.getName().replace('.', '/');
this.nameAsPath = "/" + name + ".class";
}

@Override
public Class<?> loadClass(String name) throws ClassNotFoundException {
if (name.equals(SalesRegion.class.getName()) == false) {
// Delegate to System ClassLoader.
return getParent().loadClass(name);
}

Class clazz = null;

try {
InputStream inputStream = SalesRegion.class.getResourceAsStream(nameAsPath);
if (inputStream == null) {
throw new NullPointerException("Could not find Class file");
}

ByteArrayOutputStream outputStream = new ByteArrayOutputStream();

byte[] buffer = new byte[512];
int c = 0;
while ((c = inputStream.read(buffer)) != -1) {
outputStream.write(buffer, 0, c);
}

byte[] classAsBytes = outputStream.toByteArray();

clazz = defineClass(name, classAsBytes, 0, classAsBytes.length);
}
catch (Exception e) {
throw new ClassNotFoundException(e.getMessage(), e);
}

return clazz;
}
}
}


The dummy Key that would be loaded by multiple ClassLoaders:


public interface SalesRegion {
}


Sample output:


Key: temp.demo.SalesRegion, ClassLoader: temp.demo.HackyTypeBasedStore$CustomClassLoader@c2ea3f
Data: [ABCD]

Key: temp.demo.Customer, ClassLoader: sun.misc.Launcher$AppClassLoader@fabe9
Data: [Customer-A]

Key: temp.demo.Supplier, ClassLoader: sun.misc.Launcher$AppClassLoader@fabe9
Data: [Supplier-6, Supplier-5]

Key: temp.demo.SalesRegion, ClassLoader: temp.demo.HackyTypeBasedStore$CustomClassLoader@1034bb5
Data: [KLMN, WXYZ]

Key: temp.demo.SalesRegion, ClassLoader: temp.demo.HackyTypeBasedStore$CustomClassLoader@b162d5
Data: [KLMN, ABCD]

Key: temp.demo.Employee, ClassLoader: sun.misc.Launcher$AppClassLoader@fabe9
Data: [Employee-1]

Wednesday, October 10, 2007

Expression Languages (OGNL and MVEL)

For those of you using Expression Languages in your programs to add that bit of pluggable logic fragments, I'm sure you've evaluated or probably even use OGNL. StreamCruncher uses OGNL 2.7+ to handle some of the messier parts of Expression evaluation and I've found it to be a huge time saver. What's even better is that the 2.7 version also converts the Expressions into dynamically generated Bytecode.

So, if you want to evaluate OGNL, here is a list of useful links. They are not easily locatable, so I thought this would also be a good place for me to bookmark them for future use.

Here's the old link - OGNL
The 2.7+ versions are handled by this guy Jesse - his Blog
The latest releases - on OpenSymphony

I also strongly suggest evaluating another very well done Expression Language - MVEL,which is written by Mike - his Blog

Saturday, October 06, 2007

StreamCruncher 2.2 Release Candidate

The 2.2 Release Candidate is now available. This has some important performance related changes over the 2.2 Beta version. Over the past few releases, I've spent a considerable amount of time working on parts of the Kernel to perform end-to-end processing without having to go the Database. This version performs Correlation Query processing and single Stream Query processing entirely in Memory. As a result, there are some things that don't work - like the "Order by" and "Group by" clauses. You might call it laziness, but there's only so much time I can spend on this, what with a day job and all.

Anyway, the performance has shot up to very respectable figures. The CorrelationPerfTest that I spoke about in my previous blog can now process a total of 168,000 Events per second on a single Processor, dual Core 1.8 GHz Centrino with 2 GB Memory. The Test has 3 Correlation Queries. Two of them correlate 3 Streams each and one Query correlates 2 Streams.

It's been a long journey. I'm so glad that SC can do this many Events per second now. I remember being quite worried a year and a half ago, when it could not do more than a few hundred events per second.