N-API: pass error from execute callback in napi_create_async_work to main loop

Version: v8.4.0
Platform: Linux 4.13.0-43-generic Improve repo description #48~16.04.1-Ubuntu SMP Thu May 17 12:56:46 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
Subsystem: N-API

I can't find a way to pass error from simple async operation back to main loop.
Tests for async calls napi_throw_type_error straight from execute callback, which should run in thread pool. But napi_throw_type_error does not synchronize access to VM, which, AFAIK, is not allowed, by v8 at least.

node/test/addons-napi/test_async/test_async.cc

Lines 23 to 37 in a406a32

    
           void Execute(napi_env env, void* data) { 
        
           #if defined _WIN32 
        
             Sleep(1000); 
        
           #else 
        
             sleep(1); 
        
           #endif 
        
             carrier* c = static_cast<carrier*>(data); 
        
             if (c != &the_carrier) { 
        
               napi_throw_type_error(env, nullptr, "Wrong data parameter to Execute."); 
        
               return; 
        
             } 
        
             c->_output = c->_input * 2; 
        
           }

What is correct way to pass error back? I can make my own variant using data pointer, but something like Nan::AsyncWorker::SetErrorMessage would be nice.
Availability of napi_env in napi_async_execute_callback make things more confusing - it makes me think that I can call any N-API function.

I'd need more context to understand which, but I'm guessing you want either

You may want n-api: add API for asynchronous functions (simpler version) #17887 (In review)
node_api: add napi_fatal_exception #19337 (Already landed)

#17887 is great, subscribing.

I have two concerns. Both are about "Simple Asynchronous Operations" as in documentation, running single function in threadpool, parallel to JS thread.

With NAN one could write something like that

class Worker : public Nan::AsyncWorker {
 public:
  void Execute () {
    if (true /*error happened*/) { SetErrorMessage("Something bad happened"); }
  }
};

SetErrorMessage will save message in worker instance field, then libuv will call in JS thread AsyncExecuteComplete -> WorkComplete and it will call either HandleOKCallback or HandleErrorCallback, depending on saved message.

With N-API you have to do this by hand - define structure for worker context with error message, pass it as data pointer, save message there, handle it in complete callback. It is more flexible, but, still, extra work for (as I see it) default case of running async operation.

napi_async_execute_callback executes in thread from thread pool.
One mustn't access VM from other threads, at least in v8.
But napi_async_execute_callback receives napi_env as argument, and make me think I can use it to create new JS values, call functions or throw exceptions.

n-api: add API for asynchronous functions

I believe this has been resolved. Closing. Can reopen if necessary.

n-api: add API for asynchronous functions

Navigation Menu

Repository navigation

N-API: pass error from execute callback in napi_create_async_work to main loop #20964

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

	void Execute(napi_env env, void* data) {
	#if defined _WIN32
	Sleep(1000);
	#else
	sleep(1);
	#endif
	carrier* c = static_cast<carrier*>(data);

	if (c != &the_carrier) {
	napi_throw_type_error(env, nullptr, "Wrong data parameter to Execute.");
	return;
	}

	c->_output = c->_input * 2;
	}

N-API: pass error from execute callback in napi_create_async_work to main loop #20964

Description

Activity

mhdawson commented on May 25, 2018

mcheshkov commented on May 28, 2018

jasnell commented on Jun 19, 2020

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions