我正在尝试使用NAPI创建节点模块。我必须创建一个返回诺言的异步函数。我不希望testasynfunction会阻止NodeJS事件循环。do_something_asynchronous是一个同步函数。
napi_deferred do_something_synchronous(napi_env env,napi_deferred deferred){
printf("\n3) Function called");
//napi_deferred deferred;
napi_value undefined;
napi_status status;
// Create a value with which to conclude the deferred.
status = napi_get_undefined(env, &undefined);
if (status != napi_ok) return NULL;
sleep(5);
// Resolve or reject the promise associated with the deferred depending on
// whether the asynchronous action succeeded.
if (false) {
printf("\n5) Success\nXXXXXXX");
status = napi_resolve_deferred(env, deferred, undefined);
} else {
printf("\nReject");
status = napi_reject_deferred(env, deferred, undefined);
}
if (status != napi_ok) return NULL;
// At this point the deferred has been freed, so we should assign NULL to it.
deferred = NULL;
}
//Function will be called from the js
napi_value testasynfunction(napi_env env, napi_callback_info info){
printf("XXXXX Hello \n");
napi_deferred deferred;
napi_value promise;
napi_status status;
// Create the promise.
status = napi_create_promise(env, &deferred, &promise);
if (status != napi_ok) return NULL;
printf("\n1) Calling function to do something");
do_something_synchronous(env,deferred);
//std::async(do_something_asynchronous,env,deferred);
printf("\n2) Returning Promise");
return promise;
}
napi_property_descriptor testasync = DECLARE_NAPI_METHOD("testasyn", testasynfunction);
status = napi_define_properties(env, exports, 1, &testasync);
assert(status == napi_ok);
NAPI_MODULE(NODE_GYP_MODULE_NAME, Init)
问题：1）我如何才能异步运行do_something_synchronous，以便nodejs事件循环不会被阻塞并返回诺言？
以下代码段是此异步操作的关键组件。该napi_create_async_work（）函数分配工作对象，我们可以指定工人处理函数，比如在我们的例子ExecuteMyPromise1（）（长时间运行或处理繁重的任务可以用它来部署）。此函数将作为工作池线程的队列，并且将与node.js主事件循环线程并行地异步执行。
到目前为止，一切看起来都还不错，当ExecuteMyPromise1函数计划直接从工作线程与JavaScript层交换结果时，问题就会出现。通常，只能从本机插件的主线程调用任何JavaScript操作。然后，为了进行结果交换，我们必须使用另一个将从主线程调用的本机函数。这就是为什么我们使用CompleteMyPromise1函数处理程序（如果还通过此函数完成的任何最终清理活动）的原因。当异步逻辑完成或取消时，将从主事件循环线程中调用此本地函数。
// The function called by javascript to get a promise returned.
napi_value MyPromise1(napi_env env, napi_callback_info info)
{
// -- -- -- --
// -- -- -- --
// Create a promise object.
status = napi_create_promise(env, &promDataEx->deferred, &promise);
if (status != napi_ok)
{
napi_throw_error(env, NULL, "Unable to create promise.");
}
// -- -- -- --
// -- -- -- --
{
// Create the async function.
napi_value resource_name;
napi_create_string_utf8(env, "MyPromise1", -1, &resource_name);
napi_create_async_work(env, NULL, resource_name,
ExecuteMyPromise1, CompleteMyPromise1,
promDataEx, &promDataEx->work);
napi_queue_async_work(env, promDataEx->work);
}
return promise;
}
// Execute the asynchronous work.
void ExecuteMyPromise1(napi_env env, void *data)
{
prom_data_ex_t *promDataEx = (prom_data_ex_t *)data;
// Calculate prime count
promDataEx->PrimeCount = CPrimeCount( promDataEx->x, promDataEx->y );
// Set the status as asynchronous_action is success
promDataEx->asynchronous_action_status = 0;
//sleep(3);
}
// Handle the completion of the asynchronous work.
void CompleteMyPromise1(napi_env env, napi_status status, void *data)
{
napi_value rcValue;
prom_data_ex_t *promDataEx = (prom_data_ex_t *)data;
napi_create_int32(env, promDataEx->PrimeCount, &rcValue);
// Resolve or reject the promise associated with the deferred depending on
// whether the asynchronous action succeeded.
if ( promDataEx->asynchronous_action_status == 0) // Success
{
status = napi_resolve_deferred(env, promDataEx->deferred, rcValue);
}
else
{
napi_value undefined;
status = napi_get_undefined(env, &undefined);
status = napi_reject_deferred(env, promDataEx->deferred, undefined );
}
if (status != napi_ok)
{
napi_throw_error(env, NULL, "Unable to create promise result.");
}
napi_delete_async_work(env, promDataEx->work);
free(promDataEx);
}
这里是完整的示例代码https://github.com/msatyan/MyNodeC/blob/master/src/mync1/MyPromise1.cpp
JavaScrip调用是TestPromiseWithAsync（）https://github.com/msatyan/MyNodeC/blob/master/test/TestExtensions.js
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