[Lldb-commits] Performing ManualDWARFIndex::Index() async during ManualDWARFIndex::Preload()

[Lasse Folger via lldb-commits]

Hi lldb devs,

We experienced some issues when debugging large binaries.
The startup time of lldb for large binaries is long (tens of seconds).
One of the reasons is that the *ManualDWARFIndex::Index()* function is
executed synchronously and thus blocks during startup.
We would like to change this to an async task. Let me know if you have any
concerns.

I prepared a small patch to schedule the index creation async.

I would like to have feedback on three parts:

   1. In *ManualDWARFIndex::Preload() *I capture *this* of the
   *ManualDWARFIndex*. As far as I could tell this is not a problem since
   the index is not relocated or deleted. However, I'm not that familiar with
   the architecture. Are there cases when the object is relocated or deleted
   before lldb stops?
   2. I use the *Module *mutex for synchronization because I didn't want to
   introduce a mutex in *ManualDWARFIndex *or *DWARFIndex*. Do you think
   this locking granularity is fine or should I create a dedicated mutex for
   it? Furthermore, I looked through the implementation of ManualDWARFIndex::
   *Index()* and couldn't find any locking function in there. However, I
   might have missed something (or some of the underlying implementations
   change in the future) and there is a danger for a deadlock.
   3. *ManualDWARFIndex::Index()* creates a thread pool internally. This
   means if multiple calls to* ManualDWARFIndex::Index() *are executed at
   the same time, there might be more threads than cores. This might cause
   contention and decrease efficiency. (Thanks to Andy for pointing this out).

Please let me know what you think and if I should change something.


kind regards,
Lasse
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