Hide BlockHound's own frame from the Error

[bsideup]

Since we instrument the blocking methods, we add more frames to the stack of the thrown exception. We could artificially remove them from the created java.lang.Error instance to not confuse the users with something they do not expect.

Before:

java.lang.Error: Blocking call! java.lang.Thread.sleep
	at reactor.blockhound.BlockHound$Builder.lambda$new$0(BlockHound.java:196)
	at reactor.blockhound.BlockHound$Builder.lambda$install$6(BlockHound.java:338)
	at reactor.blockhound.BlockHoundRuntime.checkBlocking(BlockHoundRuntime.java:46)
	at java.base/java.lang.Thread.sleep(Thread.java)
	at com.example.StrackTraceTest.lambda$shouldHideInternalFrames$0(StrackTraceTest.java:41)

After:

java.lang.Error: Blocking call! java.lang.Thread.sleep
	at java.base/java.lang.Thread.sleep(Thread.java)
	at com.example.StrackTraceTest.lambda$shouldHideInternalFrames$0(StrackTraceTest.java:41)

[simonbasle]

this doesn't change the size of the stackTrace array, leading to duplicated stacktrace elements 💥

verified with strings:

String[] array = new String[] { "A", "B", "C", "D" };
System.arraycopy(array, 2, array, 0, 2);

System.out.println(array.length);
for (String s : array) {
	System.out.println(s);
}

prints 4 C D C D

you can probably use Arrays.copyOfRange, or emulate its core behavior which might perform slightly better (no .class manipulation and no Array.newInstance):

System.arraycopy(original, from, copy, 0, Math.min(original.length - from, newLength));

[bsideup]

Wow! Great catch 🤦‍♂

Fixing... 😅

[bsideup]

Fixed. Thanks a lot for spotting it! 👍