IntelliJ IDEA slows down entire computer when a breakpoint is hit

Question

I am using IntelliJ IDEA 12.1.6 on (64-bit) Windows 7 Enterprise (I've also seen this same problem with IDEA 11, though not as often). I am running it under Java 7 (1.7.45).

When I run a program in the IDE, under the debugger (local debugging), everything is fine until I hit a breakpoint (these are plain old on-a-specific-line breakpoints, not method breakpoints or exception breakpoints). Once the breakpoint is hit, virtually all the time (though not always) my entire machine slows to a near halt. All keyboard operations (not just in IDEA) slow way down (they eventually do get processed so the events are buffered, not lost). Same for window operations (drag, minimize, raise, lower). Once the program resumes from the breakpoint everything goes completely back to normal until the next time a breakpoint is hit.

This is obviously really annoying as it makes debugging essentially impossible.

I've had Task Manager up and don't see anything strange. The CPU is not pegged, memory isn't maxed out, etc. My hard drive light isn't on.

Any ideas on what's going on and (more importantly) how to fix it?

Answer 1

It's hard to say what the problem is, but here are some things that might help:

• Invalidate caches as described here --though be aware of the consequences.
• Make sure you have only enabled those plugins you are actually using or likely to use.
• Try to find if all breakpoints have the same problem or if, for example, you only have issues with Java breakpoints but not JavaScript ones. If that happens, it could give you a clue.

Answer 2

Well, it looks like my specific problem is IE-related.

The program I am debugging is the server-side of a webapp. (Sadly it is IE-only due to some weird stuff in the Ajax it is using -- I'm not responsible for that).

I have been setting my breakpoints, running the server under the debugger, and then doing stuff with the webapp in IE, which ultimately causes breakpoints to be hit. When a breakpoint is hit and I am single-stepping, everything remains OK if I do not use the keyboard at all. If I click on the various single-step icons or select the single-step actions via mouse from IDEA's "Run" menu everything keeps working. But the moment I use F8 to single-step, or hit a key in any other problem (like in a mail program) the freeze happens.

It finally occurred to me (shame on me) to run IE on another computer while running the server in the IDEA debugger on my main computer. When I do that, everything is fine and I can use the keyboard in any application, as much as I want to, and the freeze does not happen.

So the problem seems to be IE causing weirdness when it has sent a request and is waiting for a response from the server. Still, there does seem to be some interaction with IDEA because when I run IE on a separate computer and hit a breakpoint on my computer, I can use the keyboard all I want on the computer where I am running IE without any problems at all.