Terminating a script mid-execution?

[Danny Dorfman]

Hello guys,

I searched through the group, but couldn't find any responses on this subject.

I'd like to run a script, and terminate it from C++ code, by the decision of a callback function.

I tried using TerminateExectuion(isolate), but the program crashes.

Here is a small sample. I assign values to the "specific" object using JavaScript.

Whenever the "alfa" field is set to "666", I'd like the script to terminate.

-----------------------------------------------------------------------------------------------------------------------------------------------------------------

  1 #include <v8.h>

  2 #include <stdio.h>

  3 using namespace v8;

  4 

  5 void SetAlfa(Local<String> property, Local<Value> value, const PropertyCallbackInfo<void>& info)

  6 {

  7     String::Utf8Value property_str(property);

  8     String::Utf8Value value_str(value);

  9     printf("SetAlfa: about to set %s=%s\n", *property_str, *value_str);

 10     Handle<Value> show_stopper = String::NewFromUtf8(info.GetIsolate(),"666");

 11     if (value->Equals(show_stopper))

 12     {

 13         printf("SetAlfa: STOPPING!\n");

 14         V8::TerminateExecution(info.GetIsolate());

 15     }

 16 }

 17 

 18 void RunIt(Isolate *isolate, const char *script_text)

 19 {

 20     printf("RunIt: about to run \"%s\"\n", script_text);

 21     Handle<String> source = String::NewFromUtf8(isolate,script_text);

 22     Handle<Script> script = Script::Compile(source);

 23     Handle<Value> result = script->Run();

 24     String::Utf8Value ascii(result);

 25     printf("RunIt: returned \"%s\"\n", *ascii);

 26 }

 27 

 28 

 29 int main(int argc, char* argv[])

 30 {

 31     Isolate* isolate = Isolate::GetCurrent();

 32     HandleScope handle_scope(isolate);

 33     Handle<Context> context = Context::New(isolate);

 34     Context::Scope context_scope(context);

 35     Handle<String> alfa_str = String::NewFromUtf8(isolate,"alfa");

 36     Handle<String> specific_str = String::NewFromUtf8(isolate,"specific");

 37 

 38     Handle<Object> specific_obj = Object::New(isolate);

 39     specific_obj->SetAccessor(alfa_str, NULL, SetAlfa);

 40     context->Global()->Set(specific_str, specific_obj);

 41 

 42     RunIt(isolate,"specific.alfa=123");

 43     RunIt(isolate,"specific.alfa=666; specific.alfa=999");

 44 

 45     return 0;

 46 }

-----------------------------------------------------------------------------------------------------------------------------------------------------------------

The output I get is:

-----------------------------------------------------------------------------------------------------------------------------------------------------------------

RunIt: about to run "specific.alfa=123"

SetAlfa: about to set alfa=123

RunIt: returned "123"

RunIt: about to run "specific.alfa=666; specific.alfa=999"

SetAlfa: about to set alfa=666

SetAlfa: STOPPING!

SetAlfa: about to set alfa=(null)

#

# Fatal error in ../src/api.cc, line 2899

# CHECK(!(isolate)->external_caught_exception()) failed

#

==== C stack trace ===============================

 1: V8_Fatal

 2: v8::Value::Equals(v8::Handle<v8::Value>) const

 3: SetAlfa(v8::Local<v8::String>, v8::Local<v8::Value>, v8::PropertyCallbackInfo<void> const&)

 4: v8::internal::PropertyCallbackArguments::Call(void (*)(v8::Local<v8::String>, v8::Local<v8::Value>, v8::PropertyCallbackInfo<void> const&), v8::Local<v8::String>, v8::Local<v8::Value>)

 5: v8::internal::JSObject::SetPropertyWithCallback(v8::internal::Handle<v8::internal::JSObject>, v8::internal::Handle<v8::internal::Object>, v8::internal::Handle<v8::internal::Name>, v8::internal::Handle<v8::internal::Object>, v8::internal::Handle<v8::internal::JSObject>, v8::internal::StrictModeFlag)

 6: v8::internal::JSObject::SetPropertyForResult(v8::internal::Handle<v8::internal::JSObject>, v8::internal::LookupResult*, v8::internal::Handle<v8::internal::Name>, v8::internal::Handle<v8::internal::Object>, PropertyAttributes, v8::internal::StrictModeFlag, v8::internal::JSReceiver::StoreFromKeyed)

 7: v8::internal::JSReceiver::SetProperty(v8::internal::Handle<v8::internal::JSReceiver>, v8::internal::LookupResult*, v8::internal::Handle<v8::internal::Name>, v8::internal::Handle<v8::internal::Object>, PropertyAttributes, v8::internal::StrictModeFlag, v8::internal::JSReceiver::StoreFromKeyed)

 8: v8::internal::JSReceiver::SetProperty(v8::internal::Handle<v8::internal::JSReceiver>, v8::internal::Handle<v8::internal::Name>, v8::internal::Handle<v8::internal::Object>, PropertyAttributes, v8::internal::StrictModeFlag, v8::internal::JSReceiver::StoreFromKeyed)

 9: v8::internal::StoreIC::Store(v8::internal::Handle<v8::internal::Object>, v8::internal::Handle<v8::internal::String>, v8::internal::Handle<v8::internal::Object>, v8::internal::JSReceiver::StoreFromKeyed)

10: ??

11: v8::internal::StoreIC_Miss(int, v8::internal::Object**, v8::internal::Isolate*)

12: ??

-----------------------------------------------------------------------------------------------------------------------------------------------------------------

                                              

Can anyone tell, what I'm doing wrong here?

Thanks in advance,

Danny

[Ben Noordhuis]

V8::TerminateExecution() doesn't terminate execution right away. It
sets a 'is terminating' flag that is checked in the generated code in
function prologues and at loop edges.

The effect of the flag is that of a pending exception and that means
it's no longer allowed to call into the VM (which many V8 API
functions do, like Value::Equals().)

Try adding a V8::IsExecutionTerminating() guard at the top of your
SetAlfa() function.

[Danny Dorfman]

Hello Ben,

I already tried that, but  V8::IsExecutionTerminating() returned false.

I don't know if it's a bug or a feature.

[Ben Noordhuis]

On Sun, Jun 22, 2014 at 8:36 AM, Danny Dorfman <wilder...@gmail.com> wrote:
> I already tried that, but V8::IsExecutionTerminating() returned false.
> I don't know if it's a bug or a feature.

I just remembered something from our code base: termination doesn't go
into effect until you enter the VM again. In our project, we force
that by executing a no-op script, see below. HTH.

void ExitFunction(const v8::FunctionCallbackInfo<v8::Value>& info) {
v8::Isolate* isolate = info.GetIsolate();
v8::HandleScope handle_scope(isolate);
// Sets a thread-local flag that is checked by the JS function prologue.
v8::V8::TerminateExecution(isolate);
// Which means it's not in effect yet.
CHECK_EQ(false, v8::V8::IsExecutionTerminating(isolate));
// Now force the termination exception by entering the VM.
v8::Local<v8::String> script_source = v8::String::NewFromUtf8(isolate, "0");
v8::TryCatch try_catch;
v8::Script::Compile(script_source)->Run();
CHECK_EQ(true, try_catch.HasCaught());
CHECK_EQ(true, try_catch.HasTerminated());
CHECK_EQ(true, v8::V8::IsExecutionTerminating(isolate));
}

[Danny Dorfman]

This is much much better. Thank you for the tip!