napi_thread_safe_promise

NAPI-Thread-Safe-Promise

• NAPI-Thread-Safe-Promise
  • Introduction
  • Usage
    • Exception handling
  • Examples
    • Async Promise Example (with macro)
    • Async Promise Example (without using macro)
    • JavaScript code for the code examples above
  • Contribution
  • License

Introduction

NOTE: This package assumes understanding of N-API

To be used in conjunction with the N-API module to call C++ code from JavaScript.

Allows the user to call thread safe promise functions such (resolve, reject) in the C++ code and return a promise to the javascript code.

Usage

1. Install the package using node package manager:

npm install napi_thread_safe_promise

1. Reference this package's include directory in binding.gyp:

'include_dirs': ["<!@(node -p \"require('napi_thread_safe_promise').include\")"],

1. Include the header in your code:

#include "promiseWrapper.h"

Note: Currently latest node version has bugs with regards to gyp so use the latest stable version (should be v14.15.3 as of now)

Exception handling

To have the ability for exceptions add the following to binding.gyp:

'cflags!': [ '-fno-exceptions' ],
'cflags_cc!': [ '-fno-exceptions' ],
'xcode_settings': {
  'GCC_ENABLE_CPP_EXCEPTIONS': 'YES',
  'CLANG_CXX_LIBRARY': 'libc++',
  'MACOSX_DEPLOYMENT_TARGET': '10.7',
},
'msvs_settings': {
  'VCCLCompilerTool': { 'ExceptionHandling': 1 },
},
'conditions': [
  ['OS=="win"', { 'defines': [ '_HAS_EXCEPTIONS=1' ] }]
]

Examples

Async Promise Example (with macro)

Napi::Promise promiseFuncJS(const CallbackInfo& info)
{
  // macro takes in info variable as input
  return PROMISE(info, {
      // now we can write our code here with access to the resolve and reject functions

      // we can now take in resolve and reject function to our threaded function because they are thread safe
      // note other variables we declared here may not be thread safe (ex. info variable is not thread safe) 
      std::thread([resolve, reject]() {
          // we can pass strings to our resolve and reject functions
          resolve("test");

          // note secondary calls to resolve or reject will have no effect
           resolve("test123");
      }).detach();

  });
}

Note: if we wish to pass json data to our resolve function we just pass in the json string to the function and parse it in the javascript code

We can use a library like https://github.com/nlohmann/json and use the dump function to accomplish this

Async Promise Example (without using macro)

Napi::Promise promiseFuncJS(const CallbackInfo& info) {
  return promiseFuncWrapper(info.Env(),
      
      [&info](resolveFunc resolve, rejectFunc reject) { // anonymous function passed to thread safe resolve and reject functions

        // here we can write our threaded code

          std::string arg1 = info[0].As<Napi::String>();
          std::thread([resolve, reject, arg1]() {
            reject(arg1);
          }).detach();
      }
  );
}

JavaScript code for the code examples above

promiseFuncJS(test)
  .then(output => {
    console.log(output);
  })
  .catch(err => {
    console.error(err);
  });

Contribution

For contribution to this package, create a pull request and the maintainer will look into it.

License

NAPI-Thread-Safe-Promise is licensed under BSD-3-Clause.