src: implement AsyncProgressQueueWorker

PR-URL: nodejs/node-addon-api#585
Fixes: nodejs/node-addon-api#582
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Gabriel Schulhof <gabriel.schulhof@intel.com>

Author: John French

doc/async_progress_worker.md renamed to doc/async_worker_variants.md

@@ -272,12 +272,12 @@ 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 <napi.h>
 
 #include <chrono>
 #include <thread>
 
-use namespace Napi;
+using namespace Napi;
 
 class EchoWorker : public AsyncProgressWorker<uint32_t> {
     public:
@@ -323,7 +323,7 @@ The following code shows an example of how to create and use an `Napi::AsyncProg
 // Include EchoWorker class
 // ..
 
-use namespace Napi;
+using namespace Napi;
 
 Value Echo(const CallbackInfo& info) {
     // We need to validate the arguments here
@@ -341,4 +341,116 @@ 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.
 
+# AsyncProgressQueueWorker
+
+`Napi::AsyncProgressQueueWorker` acts exactly like `Napi::AsyncProgressWorker`
+except that each progress committed by `Napi::AsyncProgressQueueWorker::ExecutionProgress::Send`
+during `Napi::AsyncProgressQueueWorker::Execute` is guaranteed to be
+processed by `Napi::AsyncProgressQueueWorker::OnProgress` on the JavaScript
+thread in the order it was committed.
+
+For the most basic use, only the `Napi::AsyncProgressQueueWorker::Execute` and
+`Napi::AsyncProgressQueueWorker::OnProgress` method must be implemented in a subclass.
+
+# AsyncProgressQueueWorker::ExecutionProcess
+
+A bridge class created before the worker thread execution of `Napi::AsyncProgressQueueWorker::Execute`.
+
+## Methods
+
+### Send
+
+`Napi::AsyncProgressQueueWorker::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::AsyncProgressQueueWorker` so
+after the call to `Napi::AsyncProgressQueueWorker::ExecutionProcess::Send` the data can
+be safely released.
+
+`Napi::AsyncProgressQueueWorker::ExecutionProcess::Send` guarantees invocation
+of `Napi::AsyncProgressQueueWorker::OnProgress`, which means multiple `Send`
+call will result in the in-order invocation of `Napi::AsyncProgressQueueWorker::OnProgress`
+with each data item.
+
+```cpp
+void Napi::AsyncProgressQueueWorker::ExecutionProcess::Send(const T* data, size_t count) const;
+```
+
+## Example
+
+The code below shows a basic example of the `Napi::AsyncProgressQueueWorker` implementation:
+
+```cpp
+#include <napi.h>
+
+#include <chrono>
+#include <thread>
+
+using namespace Napi;
+
+class EchoWorker : public AsyncProgressQueueWorker<uint32_t> {
+    public:
+        EchoWorker(Function& callback, std::string& echo)
+        : AsyncProgressQueueWorker(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::AsyncProgressQueueWorker` base class will store
+persistently. When the work on the `Napi::AsyncProgressQueueWorker::Execute`
+method is done the `Napi::AsyncProgressQueueWorker::OnOk` method is called and
+the results are returned 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::AsyncProgressQueueWorker`.
+
+```cpp
+#include <napi.h>
+
+// Include EchoWorker class
+// ..
+
+using 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::AsyncProgressQueueWorker` 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::AsyncProgressQueueWorker::Queue`
+method that will queue the created worker for execution.
+
 [`Napi::AsyncWorker`]: ./async_worker.md