[Lldb-commits] [PATCH] Avoid querying thread stop info if the thread hasn't been running

[Jim Ingham]

> On Jun 18, 2015, at 3:11 PM, Jim Ingham <jingham at apple.com> wrote:
> 
> I thought about this for much the same reason just a little while ago.  Turns out OS X, it is possible for us to stop a process, and fetch all the exceptions, but have some thread exception that wasn't quite ready to be delivered to that thread.  The next time you let the task run, that exception will get delivered to the thread even though it is suspended.  So it isn't safe to assume that just because WE suspended a thread, it won't have an interesting stop reason, and we had to think of another way to get around this.
> 
> Our alternate was to add a "get all thread stop reasons" packet to our extended remote protocol so once you get the stop reply packet you can turn around and get all the remaining stop reasons in one blow.

Oh, yes, and Greg is currently implementing this.

Jim


>  
> 
> That seems to me a safer way of getting pretty much the same acceleration.
> 
> Jim
> 
>> On Jun 18, 2015, at 2:42 PM, Pavel Labath <labath at google.com> wrote:
>> 
>> Hi jingham, clayborg,
>> 
>> A step over operation on a single thread typically consists of several
>> start-stop cycles (stepping over breakpoints, etc.). Currently, LLDB queries
>> the debug server for thread stop info of all threads after each stop, even
>> though the the other threads have not been running (and hence, their stop info
>> should remain the same). This introduces significant delay if the application
>> has many threads (e.g. a typical android application has about 20 threads,
>> which results in about 80 redundant packets for each step operation). This
>> commit makes LLDB reuse the stop reason from the previous stop if the thread
>> hasn't been running, thereby reducing the stepping latency.
>> 
>> http://reviews.llvm.org/D10550
>> 
>> Files:
>> source/Target/Thread.cpp
>> 
>> Index: source/Target/Thread.cpp
>> ===================================================================
>> --- source/Target/Thread.cpp
>> +++ source/Target/Thread.cpp
>> @@ -427,6 +427,12 @@
>>    }
>>    else
>>    {
>> +        if (m_temporary_resume_state == eStateStopped || m_temporary_resume_state == eStateSuspended)
>> +        {
>> +            SetStopInfo(m_stop_info_sp); // This thread hasn't been running, so the stop info is still valid.
>> +            return m_stop_info_sp;
>> +        }
>> +
>>        if ((m_stop_info_stop_id == stop_id) ||   // Stop info is valid, just return what we have (even if empty)
>>            (m_stop_info_sp && m_stop_info_sp->IsValid()))  // Stop info is valid, just return what we have
>>        {
>> @@ -746,8 +752,9 @@
>> 
>>        // If the WillResume for the plan says we are faking a resume, then it will have set an appropriate stop info.
>>        // In that case, don't reset it here.
>> +        // Also, don't reset in case we're stopped or suspended, as the stop info will remain unchanged.
>> 
>> -        if (need_to_resume && resume_state != eStateSuspended)
>> +        if (need_to_resume && resume_state != eStateSuspended && resume_state != eStateStopped)
>>        {
>>            m_stop_info_sp.reset();
>>        }
>> 
>> EMAIL PREFERENCES
>> http://reviews.llvm.org/settings/panel/emailpreferences/
>> <D10550.27963.patch>
>