Java unit testing: how to measure memory footprint for method call

Question

Assuming I have a class that does some heavy processing, operating with several collections. What I want to do is to make sure that such operation can\'t lead to out-of-memo

Answer 1

I can think of several options:

• Finding out how much memory your method requires via a microbenchmark (i.e. jmh).
• Building allocation strategies based on heuristic estimation. There are several open source solutions implementing class size estimation i.e. ClassSize. A much easier way could be utilizing a cache which frees rarely used objects (i.e. Guava's Cache). As mentioned by @EnnoShioji, Guava's cache has memory-based eviction policies.

You can also write your own benchmark test which counts memory. The idea is to

1. Have a single thread running.
2. Create a new array to store your objects to allocate. So these objects won't be collected during GC run.
3. System.gc(), memoryBefore = runtime.totalMemory() - runtime.freeMemory()
4. Allocate your objects. Put them into the array.
5. System.gc(), memoryAfter = runtime.totalMemory() - runtime.freeMemory()

This is a technique I used in my lightweight micro-benchmark tool which is capable of measuring memory allocation with byte-precision.