Question: Embedding NodeJS to run many scripts

[Let0s]

• Node.js Version: various versions compiled from source code of "v8.x" and "master" branches
• OS: MS Windows 7
• Scope: Embedding

I want to embed NodeJS into an application. My idea is following:

• make fork of node with my additional files
• build modified library
• use it in my application

but I want to run any script at any time. For access to node I wrote following code:

#include <node_version.h>
#include <v8.h>
#include <uv.h>

#include <env.h>
#include <env-inl.h>
#include <node_internals.h>
#include <node_platform.h>
#include <libplatform\libplatform.h>

namespace embed {
  const int DEFAULT_THREAD_POOL_SIZE = 4;
  bool initialized = false;
  node::NodePlatform* v8_platform;

  class Finalizer {
  public:
    ~Finalizer() {
      Fini();
    }
  }finalizer;

  //initialization v8 - once per process
  void Init() {
    if (!initialized) {
#if NODE_MAJOR_VERSION == 8
      v8_platform = new node::NodePlatform(DEFAULT_THREAD_POOL_SIZE, uv_default_loop(), nullptr);
#elif NODE_MAJOR_VERSION > 8
      v8_platform = new node::NodePlatform(DEFAULT_THREAD_POOL_SIZE, nullptr);
#endif
#if NODE_MAJOR_VERSION > 8
      node::tracing::TraceEventHelper::SetTracingController(
        new v8::TracingController());
#endif
      v8::V8::InitializePlatform(v8_platform);
      v8::V8::Initialize();

      initialized = true;
    }
  }

  //finalization v8 - once per process
  void Fini()
  {
    if (initialized) {
      v8::V8::Dispose();
      v8::V8::ShutdownPlatform();
      //v8_platform->Shutdown();
      delete v8_platform;
      v8_platform = nullptr;
      initialized = false;
    }
  }

  //running script
  void Run(int argc, const char * argv[])
  {
    node::ArrayBufferAllocator allocator;
    v8::Isolate::CreateParams params;
    params.array_buffer_allocator = &allocator;
    auto isolate = v8::Isolate::New(params);
    {
      v8::Locker locker(isolate);
      v8::Isolate::Scope isolate_scope(isolate);
      v8::HandleScope h_scope(isolate);

      v8::Local<v8::Context> context = v8::Context::New(isolate);
      v8::Context::Scope context_scope(context);
      node::IsolateData * isolate_data;
#if NODE_MAJOR_VERSION == 8
      isolate_data = node::CreateIsolateData(isolate, uv_default_loop());
#elif NODE_MAJOR_VERSION > 8
      isolate_data = node::CreateIsolateData(iso, uv_default_loop(), v8_platform);
#endif
      int exec_argc;
      const char ** exec_argv;
      node::Init(&argc, argv, &exec_argc, &exec_argv);
      auto env = node::CreateEnvironment(isolate_data,
        context,
        argc,
        argv,
        exec_argc,
        exec_argv);
      node::LoadEnvironment(env);
      node::FreeEnvironment(env);
      node::FreeIsolateData(isolate_data);
    }
    isolate->Dispose();
  }
}

All works fine (without errors) and I can call Run function many times when i want (of course, after calling Init function). But i don't like, that I must create v8::Isolate and node::Environment for every script. I tried to make one isolate for all scripts, but when I create second environment with the same isolate I get an error. I think, that one isolate and one environment for all scripts will be better way than code above. Is there a way to "reload" node::Environment with new argv? If no, is it possible to make this feature?

[bnoordhuis]

but when I create second environment with the same isolate I get an error

What error?

[Let0s]

related to this line. I think environment tries to add existing callback

[bnoordhuis]

Sorry, been a while. I suspect it's caused by the built-in performance counters or ETW support. I filed nodejs/node#18074, help welcome.

[Let0s]

It's not exactly what I wanted. The best way for me is create one isolate and one environment and just "reload" environment with new arguments for every script. But I think it's hard to realize my thoughts, isn't it?

[bnoordhuis]

Correct.

[Let0s]

I found one more bug realted to this theme.
As i described above, I use Run function for every script. But on node, builded from branches v9.x and master it runs one time. Second run doesn't work. In this line it loops and name parameter have value "natives". It caused by more than one call of node::Init function. On code from v8.x branch it works fine.
Simplest way to reproduce is:

1. Get source code of node's v9.x or master branch
2. Duplicate line with Init function call (link to line)
3. Build node exe and run it.

[Let0s]

If it can help:
OS: MS Windows 7 x64 (nodejs also x64)
My thoughts: when I call Init second time, it register modules again and make circular structure, where last node module's property nm_link links to first node module (or to another node module but not to nullptr). And nodejs try to find natives in infinite loop.

[gireeshpunathil]

@Let0s - is this still outstanding?

[Let0s]

@gireeshpunathil Yes, I think second part (with many calls Init function) is still important for embedders, because I think, that node::Init call is the only external way to pass arguments to nodejs (e.g path to script or its code).
If there is (or will be) another way, then this problem is not so important.

[gireeshpunathil]

linking with nodejs/node#19377 in expectation that it is the most relevant one.

I guess the key question that is outstanding is:

Is there a way to "reload" node::Environment with new argv?

/cc @addaleax who has been leading the embedder's use cases.

[Let0s]

Yes, this is the key question.

[gireeshpunathil]

@Let0s - multi-thread based execution environment is being proposed through nodejs/node#20876 . You can find source that was refactored, as well as few APIs added in that PR - specifically in

• src/env.cc
• src/node.cc
• src/node_platform.cc

that helps in re-entrance through a new Environment.