Hi Guy and Mikhail. I don't follow. I modified my example - see
below. You are suggesting that the locker exits the context when it
goes out of scope, but the context is fine in the 2nd scope (since I
believe the compile/run requires a context). Also, the error occurs
on the explicit Exit() - how can that happen if the Locker implicitly
enters the context?
erik
Persistent<Context> context;
{ Locker l; HandleScope handle_scope; context =
Persistent<Context>::New(Context::New()); context->Enter();}
{ Locker l; HandleScope handle_scope;
Script::Compile(String::New("1"))->Run(); context->Exit();
context.Dispose();}
On Feb 8, 2:44 pm, "Guy X. Smiley" <[email protected]> wrote:
> Hi Mikhail,
>
> I think isolates and threads are orthogonal concepts, but V8 kind of
> binds them together by requiring entry and exit - operations that put
> isolate-related information into thread-local storage.
>
> But that's neither here nor there. AFAICT the original poster's
> problem
> is caused by V8's special treatment of the default isolate, namely
> that
> locking/unlocking the default isolate implicitly triggers entry/exit.
> This
> actually makes perfect sense given V8's goal of accommodating multiple
> threading models; I just found it a bit less than obvious.
>
> On Feb 8, 5:00 pm, Mikhail Naganov <[email protected]> wrote:
>
>
>
>
>
>
>
> > Hi Guy,
>
> > Please note that isolates and threads are in fact orthogonal. An
> > isolate is a separate instance of a VM (VM state), as a thread is a
> > separate control flow. So actually you can have multiple isolates in
> > the same thread, as well as multiple threads working with the same
> > isolate. But isolates are not thread safe, so in the latter case you
> > need a locker to synchronize access from multiple threads. That's it.
>
> > On Wed, Feb 8, 2012 at 21:54, Guy X. Smiley <[email protected]> wrote:
>
> > > OK, here's how I understand it. Gurus, please correct me if I'm wrong.
>
> > > V8 supports three modes of operation - thread-oblivious, thread-safe,
> > > and
> > > multi-isolate (my terms). Thread-oblivious means you always use the
> > > default
> > > isolate and don't bother with locks. This is the default mode and is
> > > safe for
> > > single-threaded applications.
>
> > > By instantiating a locker, however, you're switching into thread-safe
> > > mode, and
> > > from that point on must always use a locker when accessing V8.
>
> > > But that's not enough. Presumably you're using thread-safe mode
> > > because your
> > > application is multi-threaded. To use V8 from a given thread, not only
> > > must you
> > > lock the relevant isolate, but the thread must also enter that
> > > isolate. This is
> > > the "assist" that thread-safe mode provides over full-blown multi-
> > > isolate mode;
> > > when you lock the default isolate, the current thread automatically
> > > enters
> > > it; when you unlock it, the current thread automatically exits it.
>
> > > So when your first locker goes out of scope, not only does it unlock
> > > the
> > > default isolate, but it also causes the thread to exit it, and that
> > > causes it
> > > to discard its record of the currently entered context.
>
> > > On Feb 7, 12:46 pm, cruisercoder <[email protected]> wrote:
> > >> The code below assets with the error "cannot exit non-entered context"
> > >> and occurs in v8 versions 3.1.8 and 3.6.2. Can anyone indicate why?
>
> > >> {
> > >> using namespace v8;
>
> > >> Persistent<Context> context;
>
> > >> {
> > >> Locker l;
> > >> HandleScope handle_scope;
> > >> context = Persistent<Context>::New(Context::New());
> > >> context->Enter();
> > >> }
>
> > >> {
> > >> Locker l;
> > >> context->Exit();
> > >> context.Dispose();
> > >> }
>
> > >> }
>
> > >> #
> > >> # Fatal error in v8::Context::Exit()
> > >> # Cannot exit non-entered context
> > >> #
>
> > > --
> > > v8-users mailing list
> > > [email protected]
> > >http://groups.google.com/group/v8-users-Hide quoted text -
>
> > - Show quoted text -
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