[lldb-dev] Listening for thread create/destroy events in python LLDB

Zachary Turner zturner at google.com
Sat Aug 1 15:21:01 PDT 2015

We get these notifications in the windows process plugin.  So if this is
something you need and you are using Windows, perhaps you could do as Jim
suggests by making the setting, but then only make it possible to turn the
setting on for platforms that support this.  Note that on Windows, you
don't need to interfere with the process to get these events, because the
OS gives the events to you, and when it gives them to you the process is
already stopped for a very short amount of time.  So this could "just work"
on Windows, meaning that the setting could be on by default (and then
perhaps off by default on other platforms)

On Sat, Aug 1, 2015 at 1:35 PM Jeffrey Tan <jeffrey.fudan at gmail.com> wrote:

> Came from a Windows world thought this is trivial to do. Thanks for the
> explanation.
> On Fri, Jul 31, 2015 at 4:34 PM, Jim Ingham <jingham at apple.com> wrote:
>> lldb doesn't attempt to generate thread creation & destruction events at
>> present.  If it did there would be a "threadCreated" event on the process,
>> but as you see there isn't...
>> There was some discussion about this a little while ago on the list.
>> IMHBSEO the debugger should interfere with the running of a program as
>> little as possible when the target is just running flat out.  So I wouldn't
>> want lldb to watch thread creation and destruction by default, since you
>> will end up starting and stopping the target much more often for
>> information that in general you don't want to see.
>> But it would be fine to add a setting that you could turn on in lldb to
>> try to catch thread create/destroy. For extra credit, you could flip this
>> on when somebody signs up for the thread creation events we would vend.
>> Anyway, IIUC gathering these events would be easy to do on Linux, since
>> you already have to be notified of new thread creation so you can attach to
>> them.
>> On OS X it would be trickier.  There is no kernel level notification of
>> thread creation or destruction.  You could get thread creation by breaking
>> on the couple of functions OS X always uses to start up new threads.
>> Getting destruction would be trickier since you'd have put a breakpoint in
>> the thread create function on the return from the thread body function.
>> That would probably be easy to tell by eyeballing the function's
>> disassembly, but might be harder to determine programmatically.
>> Feel free to file a bug or even better provide a patch if this is
>> something you really need.
>> Jim
>> > On Jul 31, 2015, at 3:13 PM, Jeffrey Tan <jeffrey.fudan at gmail.com>
>> wrote:
>> >
>> > How to receive thread create/destroy events from LLDB? I did not find a
>> broadcast bit from SBTarget or SBProcess or SBThread. I have enabled both
>> SBProcess.eBroadcastBitStateChanged and
>> SBTarget.eBroadcastBitBreakpointChanged, but still did not retrieve any
>> thread create/destroy event via SBThread.EventIsThreadEvent().
>> >
>> > I know I can query for all threads while process is paused but thread
>> can be create/destroy in run mode so it is important/useful for debugger
>> client to receive this kind of notification.
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