Calling n-api methods from own separate thread

[gryor]

• Node.js Version: v9.3.0
• OS: Arch Linux 64-bit, Kernel 4.14.6
• Scope (install, code, runtime, meta, other?): code
• Module (and version) (if relevant):

I'm trying to create a module that has an application compiled within.
The application itself needs own thread to allow node keep running simultaneously.
When the application calls n-api functions from its own thread, node will crash.
Probably a related issue is that the documentation states the environment variable must not be cached for later use. Then how could I create/get an environment for calls, which do not originate from node?

#
# Fatal error in ../deps/v8/src/isolate.h, line 536
# Debug check failed: (isolate) != nullptr.
#
(node:8606) Warning: N-API is an experimental feature and could change at any time.

Thread 7 "node" received signal SIGILL, Illegal instruction.
[Switching to Thread 0x7f1decf11700 (LWP 8615)]
v8::base::OS::Abort () at ../deps/v8/src/base/platform/platform-posix.cc:176
176         V8_IMMEDIATE_CRASH();
(gdb) bt full
#0  v8::base::OS::Abort () at ../deps/v8/src/base/platform/platform-posix.cc:176
No locals.
#1  0x00005627fd91b9a3 in V8_Fatal (file=0x5627fda7aee7 "../deps/v8/src/isolate.h", line=536, format=0x5627fdf08395 "Debug check failed: %s.")
    at ../deps/v8/src/base/logging.cc:138
        arguments = {{gp_offset = 32, fp_offset = 48, overflow_arg_area = 0x7f1decf10ab0, reg_save_area = 0x7f1decf109f0}}
#2  0x00005627fd91a938 in v8::base::(anonymous namespace)::DefaultDcheckHandler (file=0x5627fda7aee7 "../deps/v8/src/isolate.h", line=536,
    message=0x5627fda7af00 "(isolate) != nullptr") at ../deps/v8/src/base/logging.cc:56
No locals.
#3  0x00005627fd91b9cd in V8_Dcheck (file=0x5627fda7aee7 "../deps/v8/src/isolate.h", line=536, message=0x5627fda7af00 "(isolate) != nullptr")
    at ../deps/v8/src/base/logging.cc:142
No locals.
#4  0x00005627fc99ce41 in v8::internal::Isolate::Current () at ../deps/v8/src/isolate.h:536
        isolate = 0x0
#5  0x00005627fc9ae8f9 in v8::Utils::ReportApiFailure (location=0x5627fda7e63c "HandleScope::HandleScope",
    message=0x5627fda7e608 "Entering the V8 API without proper locking in place") at ../deps/v8/src/api.cc:405
        isolate = 0x7f1decf10b80
        callback = 0x5627fc9acb25 <v8::internal::ThreadManager::IsLockedByCurrentThread()+59>
#6  0x00005627fc99d769 in v8::Utils::ApiCheck (condition=false, location=0x5627fda7e63c "HandleScope::HandleScope",
    message=0x5627fda7e608 "Entering the V8 API without proper locking in place") at ../deps/v8/src/api.h:124
No locals.
#7  0x00005627fc9b10a8 in v8::HandleScope::Initialize (this=0x7f1de40923f0, isolate=0x5627ffb92350) at ../deps/v8/src/api.cc:1048
        internal_isolate = 0x5627ffb92350
        current = 0xffffffffffffff88
#8  0x00005627fc9b1035 in v8::HandleScope::HandleScope (this=0x7f1de40923f0, isolate=0x5627ffb92350) at ../deps/v8/src/api.cc:1037
No locals.
#9  0x00005627fd67138f in (anonymous namespace)::v8impl::HandleScopeWrapper::HandleScopeWrapper (this=0x7f1de40923f0, isolate=0x5627ffb92350)
    at ../src/node_api.cc:176
No locals.
#10 0x00005627fd67b6bd in napi_open_handle_scope (env=0x5627ffc2ce30, result=0x7f1decf10c68) at ../src/node_api.cc:2602
No locals.

int my_func(int id)
{
  int ret;
  napi_handle_scope scope;
  napi_value result;
  napi_value this;
  napi_value func;
  const int argc = 1;
  napi_value argv[argc];

  printf("id start %i\n", id);
  puts("trying to open scope");

  if (napi_ok != napi_open_handle_scope(env, &scope))
    napi_throw_error(env, 0, "Could not open a scope");

  puts("scope open");

  if (napi_ok != napi_get_reference_value(env, functions.this, &this))
    napi_throw_error(env, 0, "Could not get this");

  if (napi_ok != napi_get_reference_value(env, functions.id, &func))
    napi_throw_error(env, 0, "Could not get func");

  if (napi_ok != napi_create_int32(env, id, &argv[0]))
    napi_throw_error(env, 0, "Argument conversion error");

  if (napi_ok != napi_call_function(env, this, func, argc, argv, &result))
    napi_throw_error(env, 0, "Could not call javascript function");

  if (napi_ok != napi_get_value_int32(env, result, &ret))
    napi_throw_error(env, 0, "Could not retrieve the result");

  if (napi_ok != napi_close_handle_scope(env, scope))
    napi_throw_error(env, 0, "Could not close a scope");

  printf("id end %i %i\n", id, ret);

  return ret;
}

[bnoordhuis]

When the application calls n-api functions from its own thread, node will crash.

Yes, you can't do that. I'm fairly sure it's mentioned in the docs.

I believe there were plans to wrap uv_async_t to make it a little easier to make callbacks from other threads but a quick glance at the docs suggests it hasn't landed yet.

[bnoordhuis]

Found it: nodejs/node#17809 - still in progress.

[gireeshpunathil]

nodejs/node#17809 closed in lieu of nodejs/node#17887

[gireeshpunathil]

@wilhelmmatilainen - the master has the linked PR landed. Could you please check your code with that and let me know if your problem is resolved? thanks!

[gryor]

The issue is resolved with the new threadsafe functions.