src: implement AsyncProgressWorker

PR-URL: #529
Fixes: #473
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Gabriel Schulhof <gabriel.schulhof@intel.com>

doc/async_progress_worker.md

@@ -0,0 +1,344 @@
+# AsyncProgressWorker
+
+`Napi::AsyncProgressWorker` is an abstract class which implements `Napi::AsyncWorker`
+while extending `Napi::AsyncWorker` internally with `Napi::ThreadSafeFunction` for
+moving work progress reports from worker thread(s) to event loop threads.
+
+Like `Napi::AsyncWorker`, once created, execution is requested by calling
+`Napi::AsyncProgressWorker::Queue`. When a thread is available for execution
+the `Napi::AsyncProgressWorker::Execute` method will be invoked. During the
+execution, `Napi::AsyncProgressWorker::ExecutionProgress::Send` can be used to
+indicate execution process, which will eventually invoke `Napi::AsyncProgressWorker::OnProgress`
+on the JavaScript thread to safely call into JavaScript. Once `Napi::AsyncProgressWorker::Execute`
+completes either `Napi::AsyncProgressWorker::OnOK` or `Napi::AsyncProgressWorker::OnError`
+will be invoked. Once the `Napi::AsyncProgressWorker::OnOK` or `Napi::AsyncProgressWorker::OnError`
+methods are complete the `Napi::AsyncProgressWorker` instance is destructed.
+
+For the most basic use, only the `Napi::AsyncProgressWorker::Execute` and
+`Napi::AsyncProgressWorker::OnProgress` method must be implemented in a subclass.
+
+## Methods
+
+[`Napi::AsyncWorker`][] provides detailed descriptions for most methods.
+
+### 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::AsyncProgressWorker::OnOK` method and/or `Napi::AsyncProgressWorker::OnError`
+which run on the main thread and are invoked when the `Napi::AsyncProgressWorker::Execute`
+method completes.
+
+```cpp
+virtual void Napi::AsyncProgressWorker::Execute(const ExecutionProgress& progress) = 0;
+```
+
+### OnOK
+
+This method is invoked when the computation in the `Execute` method ends.
+The default implementation runs the `Callback` optionally provided when the
+`AsyncProgressWorker` class was created. The `Callback` will by default receive no
+arguments. Arguments to the callback can be provided by overriding the `GetResult()`
+method.
+
+```cpp
+virtual void Napi::AsyncProgressWorker::OnOK();
+```
+
+### OnProgress
+
+This method is invoked when the computation in the `Napi::AsyncProgressWorker::ExecutionProcess::Send`
+method was called during worker thread execution.
+
+```cpp
+virtual void Napi::AsyncProgressWorker::OnProgress(const T* data, size_t count)
+```
+
+### Constructor
+
+Creates a new `Napi::AsyncProgressWorker`.
+
+```cpp
+explicit Napi::AsyncProgressWorker(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::AsyncProgressWorker` instance which can later be queued for execution by
+calling `Napi::AsyncWork::Queue`.
+
+### Constructor
+
+Creates a new `Napi::AsyncProgressWorker`.
+
+```cpp
+explicit Napi::AsyncProgressWorker(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::AsyncProgressWorker` instance which can later be queued for execution by
+calling `Napi::AsyncWork::Queue`.
+
+### Constructor
+
+Creates a new `Napi::AsyncProgressWorker`.
+
+```cpp
+explicit Napi::AsyncProgressWorker(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::AsyncProgressWorker` instance which can later be queued for execution by
+calling `Napi::AsyncWork::Queue`.
+
+### Constructor
+
+Creates a new `Napi::AsyncProgressWorker`.
+
+```cpp
+explicit Napi::AsyncProgressWorker(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::AsyncProgressWorker` instance which can later be queued for execution by
+calling `Napi::AsyncWork::Queue`.
+
+### Constructor
+
+Creates a new `Napi::AsyncProgressWorker`.
+
+```cpp
+explicit Napi::AsyncProgressWorker(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::AsyncProgressWorker`.
+
+```cpp
+explicit Napi::AsyncProgressWorker(const Napi::Object& receiver, const Napi::Function& callback, const char* resource_name, const Napi::Object& resource);
+```
+
+- `[in] receiver`: The `this` object to be 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::AsyncProgressWorker`.
+
+```cpp
+explicit Napi::AsyncProgressWorker(Napi::Env env);
+```
+
+- `[in] env`: The environment in which to create the `Napi::AsyncProgressWorker`.
+
+Returns an `Napi::AsyncProgressWorker` instance which can later be queued for execution by calling
+`Napi::AsyncProgressWorker::Queue`.
+
+Available with `NAPI_VERSION` equal to or greater than 5.
+
+### Constructor
+
+Creates a new `Napi::AsyncProgressWorker`.
+
+```cpp
+explicit Napi::AsyncProgressWorker(Napi::Env env, const char* resource_name);
+```
+
+- `[in] env`: The environment in which to create the `Napi::AsyncProgressWorker`.
+- `[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::AsyncProgressWorker` instance which can later be queued for execution by
+calling `Napi::AsyncProgressWorker::Queue`.
+
+Available with `NAPI_VERSION` equal to or greater than 5.
+
+### Constructor
+
+Creates a new `Napi::AsyncProgressWorker`.
+
+```cpp
+explicit Napi::AsyncProgressWorker(Napi::Env env, const char* resource_name, const Napi::Object& resource);
+```
+
+- `[in] env`: The environment in which to create the `Napi::AsyncProgressWorker`.
+- `[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::AsyncProgressWorker` instance which can later be queued for execution by
+calling `Napi::AsyncProgressWorker::Queue`.
+
+Available with `NAPI_VERSION` equal to or greater than 5.
+
+### Destructor
+
+Deletes the created work object that is used to execute logic asynchronously and
+release the internal `Napi::ThreadSafeFunction`, which will be aborted to prevent
+unexpected upcoming thread safe calls.
+
+```cpp
+virtual Napi::AsyncProgressWorker::~AsyncProgressWorker();
+```
+
+# AsyncProgressWorker::ExecutionProcess
+
+A bridge class created before the worker thread execution of `Napi::AsyncProgressWorker::Execute`.
+
+## Methods
+
+### Send
+
+`Napi::AsyncProgressWorker::ExecutionProcess::Send` takes two arguments, a pointer
+to a generic type of data, and a `size_t` to indicate how many items the pointer is
+pointing to.
+
+The data pointed to will be copied to internal slots of `Napi::AsyncProgressWorker` so
+after the call to `Napi::AsyncProgressWorker::ExecutionProcess::Send` the data can
+be safely released.
+
+Note that `Napi::AsyncProgressWorker::ExecutionProcess::Send` merely guarantees
+**eventual** invocation of `Napi::AsyncProgressWorker::OnProgress`, which means
+multiple send might be coalesced into single invocation of `Napi::AsyncProgressWorker::OnProgress`
+with latest data.
+
+```cpp
+void Napi::AsyncProgressWorker::ExecutionProcess::Send(const T* data, size_t count) const;
+```
+
+## Example
+
+The first step to use the `Napi::AsyncProgressWorker` class is to create a new class that
+inherits from it and implement the `Napi::AsyncProgressWorker::Execute` abstract method.
+Typically input to the worker will be saved within the class' fields generally
+passed in through its constructor.
+
+During the worker thread execution, the first argument of `Napi::AsyncProgressWorker::Execute`
+can be used to report the progress of the execution.
+
+When the `Napi::AsyncProgressWorker::Execute` method completes without errors the
+`Napi::AsyncProgressWorker::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::AsyncProgressWorker` ensures that all the code in the `Napi::AsyncProgressWorker::Execute`
+function runs in the background out of the **event loop** thread and at the end
+the `Napi::AsyncProgressWorker::OnOK` or `Napi::AsyncProgressWorker::OnError` function will be
+called and are executed as part of the event loop.
+
+The code below shows a basic example of the `Napi::AsyncProgressWorker` implementation:
+
+```cpp
+#include<napi.h>
+
+#include <chrono>
+#include <thread>
+
+use namespace Napi;
+
+class EchoWorker : public AsyncProgressWorker<uint32_t> {
+    public:
+        EchoWorker(Function& callback, std::string& echo)
+        : AsyncProgressWorker(callback), echo(echo) {}
+
+        ~EchoWorker() {}
+    // This code will be executed on the worker thread
+    void Execute(const ExecutionProgress& progress) {
+        // Need to simulate cpu heavy task
+        for (uint32_t i = 0; i < 100; ++i) {
+          progress.Send(&i, 1)
+          std::this_thread::sleep_for(std::chrono::seconds(1));
+        }
+    }
+
+    void OnOK() {
+        HandleScope scope(Env());
+        Callback().Call({Env().Null(), String::New(Env(), echo)});
+    }
+
+    void OnProgress(const uint32_t* data, size_t /* count */) {
+        HandleScope scope(Env());
+        Callback().Call({Env().Null(), Env().Null(), Number::New(Env(), *data)});
+    }
+
+    private:
+        std::string echo;
+};
+```
+
+The `EchoWorker`'s constructor calls the base class' constructor to pass in the
+callback that the `Napi::AsyncProgressWorker` base class will store persistently. When
+the work on the `Napi::AsyncProgressWorker::Execute` method is done the
+`Napi::AsyncProgressWorker::OnOk` method is called and the results are return back to
+JavaScript when the stored callback is invoked with its associated environment.
+
+The following code shows an example of how to create and use an `Napi::AsyncProgressWorker`
+
+```cpp
+#include <napi.h>
+
+// Include EchoWorker class
+// ..
+
+use namespace Napi;
+
+Value Echo(const CallbackInfo& info) {
+    // We 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();
+}
+```
+
+The implementation of a `Napi::AsyncProgressWorker` can be used by creating a
+new instance and passing to its constructor the callback to execute when the
+asynchronous task ends and other data needed for the computation. Once created,
+the only other action needed is to call the `Napi::AsyncProgressWorker::Queue`
+method that will queue the created worker for execution.
+
+[`Napi::AsyncWorker`]: ./async_worker.md