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-# AsyncWorker
-
-`Napi::AsyncWorker` is an abstract class that you can subclass to remove many of
-the tedious tasks of moving data between the event loop and worker threads. This
-class internally handles all the details of creating and executing an asynchronous
-operation.
-
-Once created, execution is requested by calling `Napi::AsyncWorker::Queue`. When
-a thread is available for execution the `Napi::AsyncWorker::Execute` method will
-be invoked. Once `Napi::AsyncWorker::Execute` completes either
-`Napi::AsyncWorker::OnOK` or `Napi::AsyncWorker::OnError` will be invoked. Once
-the `Napi::AsyncWorker::OnOK` or `Napi::AsyncWorker::OnError` methods are
-complete the `Napi::AsyncWorker` instance is destructed.
-
-For the most basic use, only the `Napi::AsyncWorker::Execute` method must be
-implemented in a subclass.
-
-## Methods
-
-### Env
-
-Requests the environment in which the async worker has been initially created.
-
-```cpp
-Napi::Env Napi::AsyncWorker::Env() const;
-```
-
-Returns the environment in which the async worker has been created.
-
-### Queue
-
-Requests that the work be queued for execution.
-
-```cpp
-void Napi::AsyncWorker::Queue();
-```
-
-### Cancel
-
-Cancels queued work if it has not yet been started. If it has already started
-executing, it cannot be cancelled. If cancelled successfully neither
-`OnOK` nor `OnError` will be called.
-
-```cpp
-void Napi::AsyncWorker::Cancel();
-```
-
-### Receiver
-
-```cpp
-Napi::ObjectReference& Napi::AsyncWorker::Receiver();
-```
-
-Returns the persistent object reference of the receiver object set when the async
-worker was created.
-
-### Callback
-
-```cpp
-Napi::FunctionReference& Napi::AsyncWorker::Callback();
-```
-
-Returns the persistent function reference of the callback set when the async
-worker was created. The returned function reference will receive the results of
-the computation that happened in the `Napi::AsyncWorker::Execute` method, unless
-the default implementation of `Napi::AsyncWorker::OnOK` or
-`Napi::AsyncWorker::OnError` is overridden.
-
-### SuppressDestruct
-
-```cpp
-void Napi::AsyncWorker::SuppressDestruct();
-```
-
-Prevents the destruction of the `Napi::AsyncWorker` instance upon completion of
-the `Napi::AsyncWorker::OnOK` callback.
-
-### SetError
-
-Sets the error message for the error that happened during the execution. Setting
-an error message will cause the `Napi::AsyncWorker::OnError` method to be
-invoked instead of `Napi::AsyncWorker::OnOK` once the
-`Napi::AsyncWorker::Execute` method completes.
-
-```cpp
-void Napi::AsyncWorker::SetError(const std::string& error);
-```
-
-- `[in] error`: The reference to the string that represent the message of the error.
-
-### Execute
-
-This method is used to execute some tasks outside of the **event loop** on a libuv
-worker thread. Subclasses must implement this method and the method is run on
-a thread other than that running the main event loop. As the method is not
-running on the main event loop, it must avoid calling any methods from node-addon-api
-or running any code that might invoke JavaScript. Instead, once this method is
-complete any interaction through node-addon-api with JavaScript should be implemented
-in the `Napi::AsyncWorker::OnOK` method and `Napi::AsyncWorker::OnError` which run
-on the main thread and are invoked when the `Napi::AsyncWorker::Execute` method completes.
-
-```cpp
-virtual void Napi::AsyncWorker::Execute() = 0;
-```
-
-### OnOK
-
-This method is invoked when the computation in the `Execute` method ends.
-The default implementation runs the `Callback` optionally provided when the
-`AsyncWorker` class was created. The `Callback` will by default receive no
-arguments. The arguments to the `Callback` can be provided by overriding the
-`GetResult()` method.
-
-```cpp
-virtual void Napi::AsyncWorker::OnOK();
-```
-### GetResult
-
-This method returns the arguments passed to the `Callback` invoked by the default
-`OnOK()` implementation. The default implementation returns an empty vector,
-providing no arguments to the `Callback`.
-
-```cpp
-virtual std::vector<napi_value> Napi::AsyncWorker::GetResult(Napi::Env env);
-```
-
-### OnError
-
-This method is invoked after `Napi::AsyncWorker::Execute` completes if an error
-occurs while `Napi::AsyncWorker::Execute` is running and C++ exceptions are
-enabled or if an error was set through a call to `Napi::AsyncWorker::SetError`.
-The default implementation calls the `Callback` provided when the `Napi::AsyncWorker`
-class was created, passing in the error as the first parameter.
-
-```cpp
-virtual void Napi::AsyncWorker::OnError(const Napi::Error& e);
-```
-
-### Destroy
-
-This method is invoked when the instance must be deallocated. If
-`SuppressDestruct()` was not called then this method will be called after either
-`OnError()` or `OnOK()` complete. The default implementation of this method
-causes the instance to delete itself using the `delete` operator. The method is
-provided so as to ensure that instances allocated by means other than the `new`
-operator can be deallocated upon work completion.
-
-```cpp
-virtual void Napi::AsyncWorker::Destroy();
-```
-
-### Constructor
-
-Creates a new `Napi::AsyncWorker`.
-
-```cpp
-explicit Napi::AsyncWorker(const Napi::Function& callback);
-```
-
-- `[in] callback`: The function which will be called when an asynchronous
-operations ends. The given function is called from the main event loop thread.
-
-Returns a `Napi::AsyncWorker` instance which can later be queued for execution by calling
-`Queue`.
-
-### Constructor
-
-Creates a new `Napi::AsyncWorker`.
-
-```cpp
-explicit Napi::AsyncWorker(const Napi::Function& callback, const char* resource_name);
-```
-
-- `[in] callback`: The function which will be called when an asynchronous
-operations ends. The given function is called from the main event loop thread.
-- `[in] resource_name`: Null-terminated string that represents the
-identifier for the kind of resource that is being provided for diagnostic
-information exposed by the async_hooks API.
-
-Returns a `Napi::AsyncWorker` instance which can later be queued for execution by
-calling `Napi::AsyncWork::Queue`.
-
-### Constructor
-
-Creates a new `Napi::AsyncWorker`.
-
-```cpp
-explicit Napi::AsyncWorker(const Napi::Function& callback, const char* resource_name, const Napi::Object& resource);
-```
-
-- `[in] callback`: The function which will be called when an asynchronous
-operations ends. The given function is called from the main event loop thread.
-- `[in] resource_name`: Null-terminated string that represents the
-identifier for the kind of resource that is being provided for diagnostic
-information exposed by the async_hooks API.
-- `[in] resource`: Object associated with the asynchronous operation that
-will be passed to possible async_hooks.
-
-Returns a `Napi::AsyncWorker` instance which can later be queued for execution by
-calling `Napi::AsyncWork::Queue`.
-
-### Constructor
-
-Creates a new `Napi::AsyncWorker`.
-
-```cpp
-explicit Napi::AsyncWorker(const Napi::Object& receiver, const Napi::Function& callback);
-```
-
-- `[in] receiver`: The `this` object passed to the called function.
-- `[in] callback`: The function which will be called when an asynchronous
-operations ends. The given function is called from the main event loop thread.
-
-Returns a `Napi::AsyncWorker` instance which can later be queued for execution by
-calling `Napi::AsyncWork::Queue`.
-
-### Constructor
-
-Creates a new `Napi::AsyncWorker`.
-
-```cpp
-explicit Napi::AsyncWorker(const Napi::Object& receiver, const Napi::Function& callback, const char* resource_name);
-```
-
-- `[in] receiver`: The `this` object passed to the called function.
-- `[in] callback`: The function which will be called when an asynchronous
-operations ends. The given function is called from the main event loop thread.
-- `[in] resource_name`: Null-terminated string that represents the
-identifier for the kind of resource that is being provided for diagnostic
-information exposed by the async_hooks API.
-
-Returns a `Napi::AsyncWork` instance which can later be queued for execution by
-calling `Napi::AsyncWork::Queue`.
-
-### Constructor
-
-Creates a new `Napi::AsyncWorker`.
-
-```cpp
-explicit Napi::AsyncWorker(const Napi::Object& receiver, const Napi::Function& callback, const char* resource_name, const Napi::Object& resource);
-```
-
-- `[in] receiver`: The `this` object passed to the called function.
-- `[in] callback`: The function which will be called when an asynchronous
-operations ends. The given function is called from the main event loop thread.
-- `[in] resource_name`: Null-terminated string that represents the
-identifier for the kind of resource that is being provided for diagnostic
-information exposed by the async_hooks API.
-- `[in] resource`: Object associated with the asynchronous operation that
-will be passed to possible async_hooks.
-
-Returns a `Napi::AsyncWork` instance which can later be queued for execution by
-calling `Napi::AsyncWork::Queue`.
-
-
-### Constructor
-
-Creates a new `Napi::AsyncWorker`.
-
-```cpp
-explicit Napi::AsyncWorker(Napi::Env env);
-```
-
-- `[in] env`: The environment in which to create the `Napi::AsyncWorker`.
-
-Returns an `Napi::AsyncWorker` instance which can later be queued for execution by calling
-`Napi::AsyncWorker::Queue`.
-
-### Constructor
-
-Creates a new `Napi::AsyncWorker`.
-
-```cpp
-explicit Napi::AsyncWorker(Napi::Env env, const char* resource_name);
-```
-
-- `[in] env`: The environment in which to create the `Napi::AsyncWorker`.
-- `[in] resource_name`: Null-terminated string that represents the
-identifier for the kind of resource that is being provided for diagnostic
-information exposed by the async_hooks API.
-
-Returns a `Napi::AsyncWorker` instance which can later be queued for execution by
-calling `Napi::AsyncWorker::Queue`.
-
-### Constructor
-
-Creates a new `Napi::AsyncWorker`.
-
-```cpp
-explicit Napi::AsyncWorker(Napi::Env env, const char* resource_name, const Napi::Object& resource);
-```
-
-- `[in] env`: The environment in which to create the `Napi::AsyncWorker`.
-- `[in] resource_name`: Null-terminated string that represents the
-identifier for the kind of resource that is being provided for diagnostic
-information exposed by the async_hooks API.
-- `[in] resource`: Object associated with the asynchronous operation that
-will be passed to possible async_hooks.
-
-Returns a `Napi::AsyncWorker` instance which can later be queued for execution by
-calling `Napi::AsyncWorker::Queue`.
-
-### Destructor
-
-Deletes the created work object that is used to execute logic asynchronously.
-
-```cpp
-virtual Napi::AsyncWorker::~AsyncWorker();
-```
-
-## Operator
-
-```cpp
-Napi::AsyncWorker::operator napi_async_work() const;
-```
-
-Returns the N-API napi_async_work wrapped by the `Napi::AsyncWorker` object. This
-can be used to mix usage of the C N-API and node-addon-api.
-
-## Example
-
-The first step to use the `Napi::AsyncWorker` class is to create a new class that
-inherits from it and implement the `Napi::AsyncWorker::Execute` abstract method.
-Typically input to your worker will be saved within class' fields generally
-passed in through its constructor.
-
-When the `Napi::AsyncWorker::Execute` method completes without errors the
-`Napi::AsyncWorker::OnOK` function callback will be invoked. In this function the
-results of the computation will be reassembled and returned back to the initial
-JavaScript context.
-
-`Napi::AsyncWorker` ensures that all the code in the `Napi::AsyncWorker::Execute`
-function runs in the background out of the **event loop** thread and at the end
-the `Napi::AsyncWorker::OnOK` or `Napi::AsyncWorker::OnError` function will be
-called and are executed as part of the event loop.
-
-The code below shows a basic example of `Napi::AsyncWorker` the implementation:
-
-```cpp
-#include<napi.h>
-
-#include <chrono>
-#include <thread>
-
-use namespace Napi;
-
-class EchoWorker : public AsyncWorker {
- public:
- EchoWorker(Function& callback, std::string& echo)
- : AsyncWorker(callback), echo(echo) {}
-
- ~EchoWorker() {}
- // This code will be executed on the worker thread
- void Execute() {
- // Need to simulate cpu heavy task
- std::this_thread::sleep_for(std::chrono::seconds(1));
- }
-
- void OnOK() {
- HandleScope scope(Env());
- Callback().Call({Env().Null(), String::New(Env(), echo)});
- }
-
- private:
- std::string echo;
-};
-```
-
-The `EchoWorker`'s contructor calls the base class' constructor to pass in the
-callback that the `Napi::AsyncWorker` base class will store persistently. When
-the work on the `Napi::AsyncWorker::Execute` method is done the
-`Napi::AsyncWorker::OnOk` method is called and the results return back to
-JavaScript invoking the stored callback with its associated environment.
-
-The following code shows an example of how to create and use an `Napi::AsyncWorker`.
-
-```cpp
-#include<napi.h>
-
-// Include EchoWorker class
-// ..
-
-use namespace Napi;
-
-Value Echo(const CallbackInfo& info) {
- // You need to validate the arguments here.
- Function cb = info[1].As<Function>();
- std::string in = info[0].As<String>();
- EchoWorker* wk = new EchoWorker(cb, in);
- wk->Queue();
- return info.Env().Undefined();
-```
-
-Using the implementation of a `Napi::AsyncWorker` is straight forward. You only
-need to create a new instance and pass to its constructor the callback you want to
-execute when your asynchronous task ends and other data you need for your
-computation. Once created the only other action you have to do is to call the
-`Napi::AsyncWorker::Queue` method that will queue the created worker for execution.