RFR: 8277930: Add unsafe allocation event to jfr [v5]

[xpbob]

On Tue, 30 Nov 2021 11:34:12 GMT, Erik Gahlin <egahlin at openjdk.org> wrote:

> What about overhead (if JFR is disabled)?
> 
> This looks like it could be a hot path for some applications.

Thanks

**result:**
|jdk|cores|
|-|-|
|disable jfr(--disable-jvm-feature-jfr)|3.032 ± 0.059|
|remove unsafe event|2.938 ± 0.071|
|unsafe event|2.938 ± 0.065|

**env:**
os: mac os
mem:  16g 
cpu:2.6 GHz 6core Intel Core i7
framework:jmh



**testcode:**


@BenchmarkMode(Mode.Throughput)
@Warmup(iterations = 3)
@Measurement(iterations = 10, time = 5, timeUnit = TimeUnit.SECONDS)
@Threads(8)
@Fork(2)
@OutputTimeUnit(TimeUnit.MILLISECONDS)
public class UnsafeTest {

    @Benchmark
    public void mallocAndFree() throws Exception {
        Field field = Unsafe.class.getDeclaredField("theUnsafe");
        field.setAccessible(true);
        Unsafe unsafe = (Unsafe) field.get(null);
        for (int i = 0; i < 10000; i++) {
            long l = unsafe.allocateMemory(1000);
            unsafe.freeMemory(l);
        }
    }
}

-------------

PR: https://git.openjdk.java.net/jdk/pull/6591