Create v8::HandleScope outside the while loop of RunShell().

Create v8::HandleScope outside the while loop of RunShell().

We don't need to create it every single time we pass through the loop.

R=mnaganov@chromium.org

Signed-off-by: Thiago Farina <tfarina@chromium.org>;

[Vitaly Repeshko, 2011-09-03 20:00:47]

This way all the handles created in the loop will stay alive forever. This is
not something we want.


Thanks,
Vitaly

[tfarina, 2011-09-04 01:58:03]

On 2011/09/03 20:00:47, Vitaly Repeshko wrote:
> This way all the handles created in the loop will stay alive forever. This is
> not something we want.
> 
Yeah? Why they aren't destroyed with the handle_scope in the end of the
function?

So, src/d8.cc - Shell:RunShell() is wrong?

[William Hesse, 2011-09-05 07:36:42]

On 2011/09/04 01:58:03, tfarina wrote:
> On 2011/09/03 20:00:47, Vitaly Repeshko wrote:
> > This way all the handles created in the loop will stay alive forever. This
is
> > not something we want.
> > 
> Yeah? Why they aren't destroyed with the handle_scope in the end of the
> function?
> 
> So, src/d8.cc - Shell:RunShell() is wrong?

I think "forever", in this context, means as long as the while loop is running,
which could be a long time.

[tfarina, 2011-09-05 13:28:36]

On 2011/09/05 07:36:42, William Hesse wrote:
> On 2011/09/04 01:58:03, tfarina wrote:
> > On 2011/09/03 20:00:47, Vitaly Repeshko wrote:
> > > This way all the handles created in the loop will stay alive forever. This
> is
> > > not something we want.
> > > 
> > Yeah? Why they aren't destroyed with the handle_scope in the end of the
> > function?
> > 
> > So, src/d8.cc - Shell:RunShell() is wrong?
> 
> I think "forever", in this context, means as long as the while loop is
running,
> which could be a long time.

In d8 it looks like this (src/d8.cc:885-891):

static const int kBufferSize = 256;
while (true) {
  char buffer[kBufferSize];
  printf("%s", Shell::kPrompt);
  if (fgets(buffer, kBufferSize, stdin) == NULL) break;
  ExecuteString(String::New(buffer), name, true, true);
}

The HandleScope is at line 867. Keeping inside the while loop is for better
garbage collection?

[William Hesse, 2011-09-06 09:08:55]

Yes, the inner handlescope is for better GC.  Not just the input string, but any
other handles created while running that string, that aren't in a nested scope
of their own, will be kept around indefinitely if the scope isn't destroyed at
each iteration.  HandleScopes are cheap to create and destroy.

[tfarina, 2011-09-06 13:57:33]

On 2011/09/06 09:08:55, William Hesse wrote:
> Yes, the inner handlescope is for better GC.  Not just the input string, but
any
> other handles created while running that string, that aren't in a nested scope
> of their own, will be kept around indefinitely if the scope isn't destroyed at
> each iteration.  HandleScopes are cheap to create and destroy.

It seems Yangguo stolen my patch, http://codereview.chromium.org/7779032 :(

Since I end up spotting the problem in d8 I was going to fix it.