防止特定线程上的断点 - LLDB

Question

I know how to create/modify a breakpoint to stop only on a specific thread using breakpoint modify <breakpoint-id> -T <thread-name> , but can I do it the other way around, preventing the breakpoint to stop on a specific thread?

I have a log thread that use the same function I'm trying to debug on other threads and it's annoying to have to let it continue every time it hits.

Answer 1

You can do this sort of thing using the lldb Python API and Python breakpoint callbacks. The callback returns a "should stop" value, ie if it returns True, you stop at the breakpoint, and False you continue.

So for instance:

(lldb) breakpoint command add -s python -o 'return frame.thread.name != "MyThread"'

is what you wanted. Note, in this example, I didn't provide a breakpoint ID. In lldb that means "act on the last set breakpoint". But you can also supply the breakpoint ID if the one you want to add the command to doesn't happen to be the last breakpoint you set. And if you want to add it to multiple breakpoints, you can specify a breakpoint ID list.

There's more on the API's and the callback format here:

https://lldb.llvm.org/python_api.html

https://lldb.llvm.org/use/python-reference.html#running-a-python-script-when-a-breakpoint-gets-hit

Note, however, that breakpoints with should-stop callbacks will force a stop every time the breakpoint is hit. lldb auto-continues pretty quickly, so for many applications this isn't a problem. But just getting from the stop over to the debugger and back is not cheap, so if your breakpoint is in a work loop and getting hit hundreds of thousands of times a second, this is going to slow down the run. If that ends up being a problem and you control your source code, tricks like the one Eljay suggested in the comments can be really handy.