On 04/03/2013 12:25 AM, Mandy Chung wrote:
On 4/2/13 3:00 PM, Peter Levart wrote:
Hi Mandy,
There could be:
public class SM1 extends SecurityManager {
@Override
public void checkMemberAccess(Class<?> clazz, int which) {...
and:
public class SM2 extends SM1 { ... // no checkMemberAccess override
now if if you take SM2.class.getDeclaredMethod("checkMemberAccess",
...) it will throw NoSuchMethodException, but the method is
overriden in
SM1. So I think it's better to use what John suggested (although not
using getDeclaredMethod, but getMethod instead):
smgr.getClass().getMethod("checkMemberAccess",
...).getDeclaringClass() == SecurityManager.class
Are you concerned the overhead of an exception thrown that we should
avoid?
Hi Mandy,
No, I was not thinking of performance. Just the correctness.
Class.getDeclaredMethod(name, ...) only considers methods "declared"
by the class (not inherited from a superclass - directy or
indirectly). But you could have, like in example above, a hierarchy:
SM2 extends SM1 extends SecurityManager where SM1 overrides the method
in SecurityManager and SM2 doesn't. Now if you try
SM2.class.getDeclaredMethod(), you will get NoSuchMethodException, but
that does not mean the method is not overriden - it is in class SM1.
You could use getDeclaredMethod on the class and all superclasses
until reaching SecurityManager to find out if the method is overriden,
but it's fortunate that the method is public and so
Class.getMethod(name, ...) can be used which does exactly that and
already considers inheritance and overriding and returns the most
specific method in the hierarchy. Explicit search using
getDeclaredMethod() could skip searching the method in SecurityManager
class though, but:
- negative answer via exception is slow
- getMethod() only searches among public methods (which are separately
cached in special array) and can therefore be faster if there is
relatively large share of non-public methods declared in the class
being searched.
Here's a quick micro-benchmark for the common case (only one level of
subclassing the SecurityManager) and both variants (the method is
overriden in SecurityManager subclass or not):
##############################################################
# Java: 1.8.0-internal-peter_2013_01_16_13_44-b00
# VM: OpenJDK 64-Bit Server VM 25.0-b14 (mixed mode)
# OS: Linux 3.7.9-104.fc17.x86_64 (amd64)
# CPUs: 8 (virtual)
#
#-------------------------------------------------------------
# GetDeclaredMethodOverridenSearch: run duration: 3,000 ms
#
# Warm up:
# 1 threads, Tavg = 327.59 ns/op (σ = 0.00 ns/op) [ 327.59]
# 1 threads, Tavg = 326.06 ns/op (σ = 0.00 ns/op) [ 326.06]
# Measure:
1 threads, Tavg = 325.18 ns/op (σ = 0.00 ns/op) [ 325.18]
#
#-------------------------------------------------------------
# GetPublicMethodOverridenSearch: run duration: 3,000 ms
#
# Warm up:
# 1 threads, Tavg = 325.69 ns/op (σ = 0.00 ns/op) [ 325.69]
# 1 threads, Tavg = 329.67 ns/op (σ = 0.00 ns/op) [ 329.67]
# Measure:
1 threads, Tavg = 325.88 ns/op (σ = 0.00 ns/op) [ 325.88]
#
#-------------------------------------------------------------
# GetDeclaredMethodNotOverridenSearch: run duration: 3,000 ms
#
# Warm up:
# 1 threads, Tavg = 1,405.84 ns/op (σ = 0.00 ns/op) [ 1,405.84]
# 1 threads, Tavg = 1,371.14 ns/op (σ = 0.00 ns/op) [ 1,371.14]
# Measure:
1 threads, Tavg = 1,358.02 ns/op (σ = 0.00 ns/op) [ 1,358.02]
#
#-------------------------------------------------------------
# GetPublicMethodNotOverridenSearch: run duration: 3,000 ms
#
# Warm up:
# 1 threads, Tavg = 557.50 ns/op (σ = 0.00 ns/op) [ 557.50]
# 1 threads, Tavg = 553.05 ns/op (σ = 0.00 ns/op) [ 553.05]
# Measure:
1 threads, Tavg = 554.59 ns/op (σ = 0.00 ns/op) [ 554.59]
#
#-------------------------------------------------------------
# END.
##############################################################
Here's the source of the test:
public class MethodSearchTest extends TestRunner {
static final Class[] paramTypes = {Class.class, int.class};
static class SMOverriden extends SecurityManager {
@Override
public void checkMemberAccess(Class<?> clazz, int which) {
}
}
static class SMNotOverriden extends SecurityManager {
}
public static class GetDeclaredMethodOverridenSearch extends Test {
@Override
protected void doLoop(Loop loop, DevNull devNull1, DevNull devNull2,
DevNull devNull3, DevNull devNull4, DevNull devNull5) {
while (loop.nextIteration()) {
try {
SMOverriden.class.getDeclaredMethod("checkMemberAccess", paramTypes);
devNull1.yield(true);
}
catch (NoSuchMethodException e) {
devNull1.yield(false);
}
}
}
}
public static class GetPublicMethodOverridenSearch extends Test {
@Override
protected void doLoop(Loop loop, DevNull devNull1, DevNull devNull2,
DevNull devNull3, DevNull devNull4, DevNull devNull5) {
while (loop.nextIteration()) {
try {
devNull1.yield(SMOverriden.class.getMethod("checkMemberAccess",
paramTypes).getDeclaringClass() != SecurityManager.class);
}
catch (NoSuchMethodException e) {
throw new Error(e);
}
}
}
}
public static class GetDeclaredMethodNotOverridenSearch extends Test {
@Override
protected void doLoop(Loop loop, DevNull devNull1, DevNull devNull2,
DevNull devNull3, DevNull devNull4, DevNull devNull5) {
while (loop.nextIteration()) {
try {
SMNotOverriden.class.getDeclaredMethod("checkMemberAccess", paramTypes);
devNull1.yield(true);
}
catch (NoSuchMethodException e) {
devNull1.yield(false);
}
}
}
}
public static class GetPublicMethodNotOverridenSearch extends Test {
@Override
protected void doLoop(Loop loop, DevNull devNull1, DevNull devNull2,
DevNull devNull3, DevNull devNull4, DevNull devNull5) {
while (loop.nextIteration()) {
try {
devNull1.yield(SMNotOverriden.class.getMethod("checkMemberAccess",
paramTypes).getDeclaringClass() != SecurityManager.class);
}
catch (NoSuchMethodException e) {
throw new Error(e);
}
}
}
}
public static void main(String[] args) throws Exception {
startTests();
doTest(GetDeclaredMethodOverridenSearch.class, 3000L, 1, 1, 1);
doTest(GetPublicMethodOverridenSearch.class, 3000L, 1, 1, 1);
doTest(GetDeclaredMethodNotOverridenSearch.class, 3000L, 1, 1, 1);
doTest(GetPublicMethodNotOverridenSearch.class, 3000L, 1, 1, 1);
endTests();
}
}
Regards, Peter
Mandy
