[Lldb-commits] [PATCH] Implements a HostThread class.

[Zachary Turner]

Come to think of it I actually like my "alternate" method more than the way
I've done it, because it means I don't need to duplicate handles in the
assignment / copy-constructor of HostThreadWindows, because the only thing
that will get copied is the shared_ptr.


On Thu, Sep 4, 2014 at 6:18 PM, Zachary Turner <zturner at google.com> wrote:

>
>
>
> On Thu, Sep 4, 2014 at 6:06 PM, <jingham at apple.com> wrote:
>
>>
>> > On Sep 4, 2014, at 5:57 PM, Zachary Turner <zturner at google.com> wrote:
>> >
>> > Regarding point #1: I'm still not sold on this.  Exposing only the
>> HostThreadBase really complicates some things.  Some of the issues escape
>> my mind right now, but one in particular stands out.  There are a couple of
>> places where threads are copied.  I don't remember the exact file off the
>> top of my head, but something about making a copy of a thread in case the
>> thread is shutting down and nulls itself out.  With a pointer or reference
>> to a base class, this can't be done without a virtual Clone() method, which
>> is really kind of gross.
>>
>> I would like to see what is hard.  You are using a generic factory to
>> make the HostThreads, your ThreadRunner, and then you are calling generic
>> methods on them.  Maybe I'm too stuck on this, but it seems like we should
>> keep host specific stuff out of generic lldb functionality, and enforce
>> that with the compiler, not with buildbots on the lacking host failing
>> sometime later on...  That just seems ugly to me.
>
>
> It's not that it's hard, I guess it's just a difference of opinion on
> what's the most ugly.  Consider the following block of code which uses raw
> lldb:thread_t's.
>
> lldb::thread_t backup = m_thread;
> ...
> m_thread = backup;
>
> With my patch, that becomes the following:
>
> HostThread backup = m_thread;
> ...
> m_thread = backup;
>
> With the base class method, that becomes the following:
>
> HostThreadBaseSP backup = m_thread->Clone();
> ...
> m_thread = backup->Clone();
>
> These look similar, but behind the scenes it's ugly.  You now need a pure
> virtual Clone() method on HostThreadBase (trivial to implement of course,
> but it's just code pollution).  You need to store by pointer instead of by
> value, which means you have to worry about null-checks as well.
>
> There is the issue you mention which is that only a buildbot will tell you
> if you use a platform-specific method, but my argument is just that this is
> strictly better than before, because before *nobody* would tell you when
> you used a platform-specific method.  It would just be a no-op.
>
> That said, I have another idea in case you're still opposed to the way
> I've done it.  Basically, just have HostThread.  Nothing derives from it.
>  Its only member is a shared_ptr<HostNativeThread>.  HostNativeThread does
> have subclasses just as the current HostThreadBase does.  The methods of
> HostThread just forward their calls to HostNativeThread, but also
> HostThread provides a method called GetNativeThread() which returns
> HostNativeThread automatically cast to the most-derived type.
>
> This way, in generic code, as long as you don't write
> thread.GetNativeThread(), you're guaranteed to only be using generic
> methods.
>
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