如何在 Java 中分析阻塞代码——测量执行时间而不是 CPU 时间

Question

I am trying to profile that is often blocking in either database and rest calls. The code is not cpu bound. The following sample junit methods should illustrate the issue:

@RepeatedTest(10)
void fast() throws InterruptedException {
    Thread.sleep(100);
}

@RepeatedTest(10)
void slow() throws InterruptedException {
    // imagine a slow database or rest call or any other blocking code
    Thread.sleep(1000);
}

I am using IntelliJ and Java Flight Recorder. I expect that method fast is reported as using about 10% of execution time and method slow is using about 90% of execution time. But they are not reported at all because they don't eat CPU time.

How can I profile the real execution time that includes waiting time in blocking code instead of CPU time only?

Answer 1

You need a profiler that understands the semantics of JDBC and HTTP calls. For example, with JProfiler, the profiling agent captures a synthetic Net I/O thread state that is included when the thread status selector is set to "All states".

Disclaimer: My company develops JProfiler

Answer 2

Async profiler is an excellent, free, and very lightweight tool for JVM profiling. In typical settings, it indeed measures on-CPU time but it has an option to do "Wall-clock" profiling: https://github.com/jvm-profiling-tools/async-profiler#wall-clock-profiling

You can experiment with that and see if that gives you better results.