I am trying to record the count of "Object.wait" method calls. Intercept "public final native void wait(long timeout)" is invalid with ByteBuddy. I did some tests:
test1、test2 print error: java.lang.IllegalStateException: Cannot call super (or default) method for public final void java.lang.Object.wait(long,int) throws java.lang.InterruptedException; java.lang.IllegalStateException: Cannot call super (or default) method for public final native void java.lang.Object.wait(long) throws java.lang.InterruptedException
test3 is invalid, print nothing.
test4 is success.
Here is my test code:
Javaagent:
final public class AgentBootstrap {
public static class TestAdvice {
@Advice.OnMethodEnter
public static void before(@Advice.Origin String methodIns) {
System.out.println("Byte-Buddy enter:" + methodIns);
}
@Advice.OnMethodExit
public static void after(@Advice.Origin String methodIns) {
System.out.println("Byte-Buddy after:" + methodIns);
}
}
public static void premain(String agentArgs, Instrumentation inst) throws Exception{
AgentBuilder agentBuilder = new AgentBuilder.Default()
.with(AgentBuilder.RedefinitionStrategy.RETRANSFORMATION)
.with(AgentBuilder.InitializationStrategy.NoOp.INSTANCE)
.with(AgentBuilder.TypeStrategy.Default.REBASE)
.enableNativeMethodPrefix("$$mynative_")
.with(AgentBuilder.Listener.StreamWriting.toSystemError().withErrorsOnly())
.with(AgentBuilder.InstallationListener.StreamWriting.toSystemError())
.ignore(nameStartsWith("net.bytebuddy."));
// test1(agentBuilder, inst);
// test2(agentBuilder, inst);
// test3(agentBuilder, inst);
// test4(agentBuilder, inst);
}
/**
* intercept method: public final native void wait(long timeout)
* print error: java.lang.IllegalStateException: Cannot call super (or default) method for public final native void java.lang.Object.wait(long) throws java.lang.InterruptedException
*/
private static void test1(AgentBuilder agentBuilder, Instrumentation inst) throws Exception {
agentBuilder.disableClassFormatChanges()
.type(is(Object.class))
.transform(new Transformer() {
@Override
public Builder<?> transform(Builder<?> builder, TypeDescription typeDescription, ClassLoader classLoader,JavaModule module) {
return builder.method(named("wait").and(takesArguments(1))).intercept(Advice.to(TestAdvice.class));
}
})
.installOn(inst);
inst.retransformClasses(Object.class);
}
/**
* intercept method: public final void wait(long timeout, int nanos)
* print error: java.lang.IllegalStateException: Cannot call super (or default) method for public final void java.lang.Object.wait(long,int) throws java.lang.InterruptedException
*/
private static void test2(AgentBuilder agentBuilder, Instrumentation inst) throws Exception {
agentBuilder.disableClassFormatChanges()
.type(is(Object.class))
.transform(new Transformer() {
@Override
public Builder<?> transform(Builder<?> builder, TypeDescription typeDescription, ClassLoader classLoader,JavaModule module) {
return builder.method(named("wait").and(takesArguments(2))).intercept(Advice.to(TestAdvice.class));
}
})
.installOn(inst);
inst.retransformClasses(Object.class);
}
/**
* intercept method: public final native void wait(long timeout)
* invalid, print nothing
*/
private static void test3(AgentBuilder agentBuilder, Instrumentation inst) throws Exception {
agentBuilder.disableClassFormatChanges()
.type(is(Object.class))
.transform(new Transformer() {
@Override
public Builder<?> transform(Builder<?> builder, TypeDescription typeDescription, ClassLoader classLoader,JavaModule module) {
return builder.visit(Advice.to(TestAdvice.class).on(named("wait").and(takesArguments(1))));
}
})
.installOn(inst);
inst.retransformClasses(Object.class);
}
/**
* intercept method: public final void wait(long timeout, int nanos)
* success
*/
private static void test4(AgentBuilder agentBuilder, Instrumentation inst) throws Exception {
agentBuilder.type(is(Object.class))
.transform(new Transformer() {
@Override
public Builder<?> transform(Builder<?> builder, TypeDescription typeDescription, ClassLoader classLoader,JavaModule module) {
return builder.visit(Advice.to(TestAdvice.class).on(named("wait").and(takesArguments(2))));
}
})
.installOn(inst);
}
}
Test:
public static void main(String[] args) throws Exception {
new Thread(() -> {
Object obj = new Object();
while (true){
try {
synchronized (obj) {
obj.wait(1000);
obj.wait(1000, 1);
}
}catch (Exception e) {
e.printStackTrace();
}
}
}).start();
}
:( Test4 code is for "public final void wait()" method, it works, but it doesn't work for "public final native void wait()" method. I want to know how to intercept "public final native void wait()" method.
Looking into this, there is actually a bug in Byte Buddy version 1.10.14. The rebased method must have the modifiers private final and not just private, otherwise, the JVM will not accept the rebased method.
The fix is already on master, if you build Byte Buddy yourself, you should be able to run your agent now. The next version 1.10.15 will contain this fix.
Do however note that the JVM does no longer support adding private (final) methods from version 13 on upwards. The old behavior can be reset using -XX:+AllowRedefinitionToAddDeleteMethods. This option is however deprecated and will no longer exist in a future version of the JVM. Without such a possibility to rename the native method, this behavior is no longer possible on the JVM, with or without Byte Buddy.
(For disclosure, I am the maintainer of Byte Buddy.)