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package com.sun.ejb.containers.util;
import java.util.Map;
import java.util.HashMap;
import java.util.Set;
import java.util.HashSet;
import java.util.Iterator;
import java.lang.reflect.Method;
/**
* This is an optimized map for resolving java.lang.reflect.Method objects.
* Doing a method lookup, even on an unsynchronized Map, can be an
* expensive operation, in many cases taking multiple microseconds.
* In most situations this overhead is negligible, but it can be noticeable
* when performed in the common path of a local ejb invocation, where our
* goal is to be as fast as a raw java method call.
*
* A MethodMap must be created with an existing Map and is immutable after
* construction(except for clear()).
* It does not support the optional Map operations
* put, putAll, and remove. NOTE that these operations could
* be implemented but are not necessary at this point since the main use
* is for the container's method info, which is invariant after initialization.
*
* As this is a map for Method objects, null keys are not supported.
* This map is unsynchronized.
*/
public final class MethodMap extends HashMap {
// If bucket size is not specified by caller, this is the number
// of buckets per method that will be created.
private static final int DEFAULT_BUCKET_MULTIPLIER = 20;
private int numBuckets_;
// Sparse array of method info. Each element represents one method
// or is null. Array is hashed by a combination of the
// method name's hashcode and its parameter length. See
// getBucket() below for more details.
//
// Note that reference equality is not very useful on Method since
// it defines the equals() method and each call to Class.getMethods()
// returns new Method instances.
private MethodInfo[] methodInfo_;
public MethodMap(Map methodMap) {
super(methodMap);
numBuckets_ = methodMap.size() * DEFAULT_BUCKET_MULTIPLIER;
buildLookupTable(methodMap);
}
public MethodMap(Map methodMap, int numBuckets) {
super(methodMap);
if( numBuckets <= 0 ) {
throw new IllegalArgumentException
("Invalid value of numBuckets = " + numBuckets);
}
numBuckets_ = numBuckets;
buildLookupTable(methodMap);
}
public Object put(Object key, Object value) {
throw new UnsupportedOperationException();
}
public void putAll(Map t) {
throw new UnsupportedOperationException();
}
public Object remove(Object key) {
throw new UnsupportedOperationException();
}
public Object get(Object key) {
if( key instanceof Method ) {
Method m = (Method) key;
Class[] paramTypes = m.getParameterTypes();
return get(m, paramTypes.length);
}
return null;
}
public Object get(Method m, int numParams) {
if( methodInfo_ == null ) {
return null;
} else if( numParams < 0 ) {
throw new IllegalStateException
("invalid numParams = " + numParams);
}
Object value = null;
MethodInfo methodInfo = methodInfo_[getBucket(m, numParams)];
if( methodInfo != null) {
// Declaring classes must be the same for methods to be equal.
if(methodInfo.declaringClass == m.getDeclaringClass()) {
value = methodInfo.value;
}
}
return (value != null) ? value : super.get(m);
}
public void clear() {
if( methodInfo_ != null ) {
methodInfo_ = null;
super.clear();
}
}
private void buildLookupTable(Map methodMap) {
methodInfo_ = new MethodInfo[numBuckets_];
Set occupied = new HashSet();
for(Iterator iter = methodMap.entrySet().iterator(); iter.hasNext();) {
Map.Entry entry = (Map.Entry)iter.next();
Object nextObj = entry.getKey();
Method next = null;
if( nextObj == null ) {
throw new IllegalStateException("null keys not supported");
} else if( nextObj instanceof Method ) {
next = (Method) nextObj;
} else {
throw new IllegalStateException
("invalid key type = " + nextObj.getClass() +
" key must be of type java.lang.reflect.Method");
}
int bucket = getBucket(next);
if( !occupied.contains(bucket) ) {
MethodInfo methodInfo = new MethodInfo();
methodInfo.value = entry.getValue();
// cache declaring class so we can avoid the method call
// during lookup operation.
methodInfo.declaringClass = next.getDeclaringClass();
methodInfo_[bucket] = methodInfo;
occupied.add(bucket);
} else {
// there's a clash for this bucket, so null it out and
// defer to backing HashMap for results.
methodInfo_[bucket] = null;
}
}
}
private final int getBucket(Method m) {
// note : getParameterTypes is guaranteed to be 0-length array
// (as opposed to null) for a method with no arguments.
Class[] paramTypes = m.getParameterTypes();
return getBucket(m, paramTypes.length);
}
private final int getBucket(Method m, int numParams) {
String methodName = m.getName();
// The normal Method.hashCode() method makes 5 method calls
// and does not cache the result. Here, we use the method name's
// hashCode since String.hashCode() makes 0 method calls *and* caches
// the result. The tradeoff is that using only method name will
// not account for overloaded methods, so we also add the number of
// parameters to the calculation. In many cases, the caller
// already knows the number of parameters, so it can be passed in
// to the lookup. This gives up some encapsulation for
// speed. It will result in better performance because
// we can skip the call to m.getClass().getParameterTypes(),
// which results in multiple method calls and can involve some
// expensive copying depending of the types themselves.
// Of course, this still won't account for the case where methods
// are overloaded with the same number of parameters but different
// types. However, the cache miss penalty should be small enough
// in this case that it's a fair tradeoff. Adding anything else
// to the hashcode calculation will have too large an impact on the
// common case.
int hashCode = methodName.hashCode();
// account for negative hashcodes
hashCode = (hashCode >= 0) ? hashCode : (hashCode * -1);
hashCode = (hashCode > numParams) ?
(hashCode - numParams) : (hashCode + numParams);
return (hashCode % numBuckets_);
}
private static class MethodInfo {
public Class declaringClass;
public Object value;
}
}