Product Version: NetBeans IDE Dev (Build 201512240002)
Java: 1.8.0_66; Java HotSpot(TM) 64-Bit Server VM 25.66-b17
Runtime: Java(TM) SE Runtime Environment 1.8.0_66-b17
System: Windows 10 version 10.0 running on amd64; Cp1252; en_CA (nb)
User directory: C:\Users\Gili\AppData\Roaming\NetBeans\dev
Cache directory: C:\Users\Gili\AppData\Local\NetBeans\Cache\dev

I have a strong suspicion that something is wrong with the implementation of conditional breakpoints. The following testcase demonstrates equivalent code running 10,000 times faster when toggling between conditional and non-conditional breakpoints even though the non-conditional breakpoint is still only getting invoked when the condition is true.

Testcase:

1. Create a Java application with the following code:

import java.time.Duration;
import java.time.Instant;
import java.util.Random;

public class ConditionalBreakpoints {

    public static void main(String[] args) {
        Random random = new Random(0);
        Instant start = Instant.now();
        for (int i = 0; i < 10_000; ++i) {
            int value = random.nextInt();
            if (value == 123456) {
                System.out.println("Set a non-conditional breakpoint here");
            }
            assert (value != 123456) : "Set a conditional breakpoint here";
        }
        System.out.println("Duration: " + Duration.between(start, Instant.now()));
    }
}

2. If you run this code you will notice that neither conditional is ever true (neither the println() nor assert never run); however, adding a debugging breakpoint increases the runtime of the application by over 10,000 times.
3. Set a conditional breakpoint on the second println() with condition "value == 123456".
4. Debug project (CTRL+F5). On my machine, runtime is 12 seconds.
5. Delete or disable the breakpoint from step 2. Add a non-conditional breakpoint on the first println().
6. Debug project (CTRL+F5). On my machine, runtime is 1ms.

As you can see, in both cases the breakpoints are only hit when the conditional is true.

Is it possible for Netbeans to implement conditional breakpoints in terms of non-conditional breakpoints as seen above? Perhaps you could rewrite method bytecode on-the-fly to add the conditional directly into the method (with a non-conditional breakpoint) instead of using JPDA if the latter is too slow?

What do you think?