AsyncAdd3ImplicitExample

This example illustrates implementing a complex asynchronous function using WsAsyncExecute.

The example implements an asynchronous function 'AddThree' which adds three integers together by building upon an existing Add function which can add two integers asynchronously.

AsyncAdd3Implicit.cpp

//------------------------------------------------------------
// Copyright (C) Microsoft.  All rights reserved.
//------------------------------------------------------------

#ifndef UNICODE
#define UNICODE
#endif

#include <windows.h>
#include <stdio.h>
#include <WebServices.h>

#pragma comment(lib, "WebServices.lib")

// Worker function that adds two numbers
HRESULT DoAdd(int a, int b, int* result, WS_ERROR* error)
{
    HRESULT hr;
    static const WS_STRING errorString = WS_STRING_VALUE(L"Negative numbers are not supported.");

    // To illustrate error handling, we won't support negative numbers
    if (a < 0 || b < 0)
    {
        // Add error information to error object  
        if (error != NULL)
        {
            WsAddErrorString(error, &errorString);
        }

        hr = E_NOTIMPL;
    }
    else
    {
        *result = a + b;
        hr = NOERROR;
    }

    return hr;
}

// A struct to maintain the in/out parameters to the Add function
struct AddParameters
{
    int a;
    int b;
    int* sumPointer;
    WS_ERROR* error;
    WS_ASYNC_CONTEXT asyncContext;
};

// A thread function that adds two numbers
DWORD WINAPI AdderThread(void* threadParameter)
{
    // Get the parameters for Add which were passed in CreateThread
    AddParameters* addParameters = (AddParameters*)threadParameter;

    // Do the addition
    HRESULT hr = DoAdd(
        addParameters->a, 
        addParameters->b, 
        addParameters->sumPointer, 
        addParameters->error);

    // Make a copy of the async context
    WS_ASYNC_CONTEXT asyncContext = addParameters->asyncContext;

    // Free the parameters
    HeapFree(GetProcessHeap(), 0, addParameters);

    // Notify the caller that the async operation is complete
    // Since we have a dedicated thread for the callback, we can invoke long
    (asyncContext.callback)(hr, WS_LONG_CALLBACK, asyncContext.callbackState);

    return 1;
}

// An example of a function that can be called asynchronously
HRESULT Add(int a, int b, int* sumPointer, const WS_ASYNC_CONTEXT* asyncContext, WS_ERROR* error)
{
    if (asyncContext == NULL)
    {
        // Invoked synchronously, so do the addition on calling thread
        return DoAdd(a, b, sumPointer, error);
    }
    else
    {
        // Invoked asynchronously

        // Decide whether to complete synchronously or asynchronously
        if (b == 0)
        {
            // Complete synchronously.  We have this case just as an illustration
            // that synchronous completion is possible when invoked asynchronously.
            return DoAdd(a, b, sumPointer, error);
        }
        else
        {
            // Complete asynchronously

            // Alloc space for in/out parameters
            AddParameters* addParameters;
            addParameters = (AddParameters*)HeapAlloc(GetProcessHeap(), 0, sizeof(AddParameters));
            if (addParameters == NULL)
            {
                return E_OUTOFMEMORY;
            }

            // Make a copy of in/out parameters
            addParameters->a = a;
            addParameters->b = b;
            addParameters->sumPointer = sumPointer;
            addParameters->error = error;
            addParameters->asyncContext = *asyncContext;

            // Create a thread which will do the work, passing parameters
            HANDLE threadHandle = CreateThread(NULL, 0, AdderThread, addParameters, 0, NULL);
            if (threadHandle == NULL)
            {
                // Free the parameters
                HeapFree(GetProcessHeap(), 0, addParameters);
                return HRESULT_FROM_WIN32(GetLastError());
            }

            // Close returned thread handle
            CloseHandle(threadHandle);

            // Indicate asynchronous completion
            return WS_S_ASYNC;
        }
    }
}

// Caller allocated state for use by AddThree.  In c++, this might be a class and
// the caller would be unaware of the internal details.
struct ADD_STATE
{
    WS_ASYNC_STATE asyncState;
    int a;
    int b;
    int c;
    int sum;
    int* result;
};

HRESULT CALLBACK Add1(HRESULT hr, WS_CALLBACK_MODEL callbackModel, void* state, WS_ASYNC_OPERATION* next, const WS_ASYNC_CONTEXT* asyncContext, WS_ERROR* error);

HRESULT CALLBACK Add2(HRESULT hr, WS_CALLBACK_MODEL callbackModel, void* state, WS_ASYNC_OPERATION* next, const WS_ASYNC_CONTEXT* asyncContext, WS_ERROR* error);

HRESULT CALLBACK Add3(HRESULT hr, WS_CALLBACK_MODEL callbackModel, void* state, WS_ASYNC_OPERATION* next, const WS_ASYNC_CONTEXT* asyncContext, WS_ERROR* error);

HRESULT CALLBACK Add1(HRESULT hr, WS_CALLBACK_MODEL callbackModel, void* state, WS_ASYNC_OPERATION* next, const WS_ASYNC_CONTEXT* asyncContext, WS_ERROR* error)
{
    UNREFERENCED_PARAMETER(callbackModel);

    ADD_STATE* addState = (ADD_STATE*)state;
    if (FAILED(hr))
    {
        return hr;
    }
    // Set up the next function execute after Add completes
    next->function = Add2;
    return Add(addState->a, addState->b, &addState->sum, asyncContext, error);
}

HRESULT CALLBACK Add2(HRESULT hr, WS_CALLBACK_MODEL callbackModel, void* state, WS_ASYNC_OPERATION* next, const WS_ASYNC_CONTEXT* asyncContext, WS_ERROR* error)
{
    UNREFERENCED_PARAMETER(callbackModel);

    ADD_STATE* addState = (ADD_STATE*)state;
    if (FAILED(hr))
    {
        return hr;
    }
    // Set up the next function execute after Add completes
    next->function = Add3;
    return Add(addState->sum, addState->c, &addState->sum, asyncContext, error);
}

HRESULT CALLBACK Add3(HRESULT hr, WS_CALLBACK_MODEL callbackModel, void* state, WS_ASYNC_OPERATION* next, const WS_ASYNC_CONTEXT* asyncContext, WS_ERROR* error)
{
    UNREFERENCED_PARAMETER(callbackModel);
    UNREFERENCED_PARAMETER(next);
    UNREFERENCED_PARAMETER(asyncContext);
    UNREFERENCED_PARAMETER(error);

    ADD_STATE* addState = (ADD_STATE*)state;
    if (FAILED(hr))
    {
        return hr;
    }
    // The operation succeeded, set the out parameter
    *addState->result = addState->sum;
    // No more functions to execute, so don't set next->function, and WsAsyncExecute will terminate.
    return NOERROR;
}

HRESULT CALLBACK AddThree(ADD_STATE* addState, int a, int b, int c, int* result, const WS_ASYNC_CONTEXT* asyncContext, WS_ERROR* error)
{
    // Set up the state for the operation
    addState->a = a;
    addState->b = b;
    addState->c = c;
    addState->sum = 0;
    addState->result = result;
    // Start the operation at Add1
    return WsAsyncExecute(&addState->asyncState, Add1, WS_SHORT_CALLBACK, addState, asyncContext, error);
}

void CALLBACK AddThreeComplete(HRESULT hr, WS_CALLBACK_MODEL callbackModel, void* state)
{
    UNREFERENCED_PARAMETER(hr);
    UNREFERENCED_PARAMETER(callbackModel);

    HANDLE handle = (HANDLE)state;
    SetEvent(handle);
}

// Main entry point
int __cdecl wmain(int argc, __in_ecount(argc) wchar_t **argv)
{
    UNREFERENCED_PARAMETER(argc);
    UNREFERENCED_PARAMETER(argv);
    
    HRESULT hr = NOERROR;
    
    // Some numbers to add asynchronously
    // Add has the behavior that if the second parameter is 0, it will perform synchronously
    int ints[] = 
    { 
        1, 0, 0, // First add sync,  second add sync
        2, 1, 0, // First add async, second add sync
        3, 0, 2, // First add sync,  second add async
        4, 3, 2, // First add async, second add async
    };
    
    // Set up the event that will get signaled each time AddThree is complete
    HANDLE handle = CreateEvent(NULL, FALSE, FALSE, NULL);
    if (handle == NULL)
    {
        goto Exit;
    }
    
    // Set up the callback to use when performing the addition asynchronously
    WS_ASYNC_CONTEXT addThreeComplete;
    addThreeComplete.callback = AddThreeComplete;
    addThreeComplete.callbackState = handle;
    
    // Declare private data for AddThree
    ADD_STATE addState;
    
    // Perform the additions synchronously and asynchronously
    for (ULONG loop = 0; loop < 2; loop++)
    {
        // Add sets of integers that will cause different execution behavior when added asynchronously
        for (ULONG i = 0; i < sizeof(ints) / sizeof(int); i += 3)
        {
            wprintf(L"Adding %d,%d,%d %s...\n", ints[i], ints[i + 1], ints[i + 2], (loop == 0 ? L"synchronously" : L"asynchronously"));
    
            // Set up how the function will be called
            WS_ASYNC_CONTEXT* asyncContext;
            if (loop == 0)
            {
                // Perform the addition synchronously
                asyncContext = NULL;
            }
            else
            {
                // Perform the addition asynchronously
                asyncContext = &addThreeComplete;
            }
    
            // Perform the addition
            int sum;
            hr = AddThree(&addState, ints[i], ints[i + 1], ints[i + 2], &sum, asyncContext, NULL);
    
            if (hr == WS_S_ASYNC)
            {
                // If the operation is being performed asynchronously, then wait for it to complete
                WaitForSingleObject(handle, INFINITE);
            }
            if (SUCCEEDED(hr))
            {
                wprintf(L"Result: %d\n", sum);
            }
            else
            {
                wprintf(L"AddThree failed.\n");
            }
        }
    }
    Exit:
    if (handle != NULL)
    {
        CloseHandle(handle);
    }
    fflush(stdout);
    return SUCCEEDED(hr) ? 0 : -1;
}