A Java agent that rewrites bytecode to instrument allocation sites
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Latest commit 58d8473 Oct 25, 2018


The Allocation Instrumenter is a Java agent written using the java.lang.instrument API and ASM. Each allocation in your Java program is instrumented; a user-defined callback is invoked on each allocation.

How to get it

The latest release is available from Maven Central as:


Basic usage

In order to write your own allocation tracking code, you have to implement the Sampler interface and pass an instance of that to AllocationRecorder.addSampler():

AllocationRecorder.addSampler(new Sampler() {
  public void sampleAllocation(int count, String desc, Object newObj, long size) {
    System.out.println("I just allocated the object " + newObj +
      " of type " + desc + " whose size is " + size);
    if (count != -1) { System.out.println("It's an array of size " + count); }

You can also use the allocation instrumenter to instrument constructors of particular classes. You do this by instantiating a ConstructorCallback and passing it to ConstructorInstrumenter.instrumentClass():

try {
      Thread.class, new ConstructorCallback<Thread>() {
        @Override public void sample(Thread t) {
          System.out.println("Instantiating a thread");
} catch (UnmodifiableClassException e) {
  System.out.println("Class cannot be modified");

For more information on how to get or use the allocation instrumenter, see Getting Started.