异步函数示例
此示例演示了如何实现和调用异步函数。
该示例由以下部分组成：
- Add 函数，它将以同步或异步方式添加两个数字。 它创建一个线程作为异步案例的实现详细信息。
- CallAddSync 函数同步调用 Add 函数。
- CallAddAsync 函数异步调用 Add 函数。
AsyncModel.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")
// Print out rich error info
void PrintError(HRESULT errorCode, WS_ERROR* error)
{
wprintf(L"Failure: errorCode=0x%lx\n", errorCode);
if (errorCode == E_INVALIDARG || errorCode == WS_E_INVALID_OPERATION)
{
// Correct use of the APIs should never generate these errors
wprintf(L"The error was due to an invalid use of an API. This is likely due to a bug in the program.\n");
DebugBreak();
}
HRESULT hr = NOERROR;
if (error != NULL)
{
ULONG errorCount;
hr = WsGetErrorProperty(error, WS_ERROR_PROPERTY_STRING_COUNT, &errorCount, sizeof(errorCount));
if (FAILED(hr))
{
goto Exit;
}
for (ULONG i = 0; i < errorCount; i++)
{
WS_STRING string;
hr = WsGetErrorString(error, i, &string);
if (FAILED(hr))
{
goto Exit;
}
wprintf(L"%.*s\n", string.length, string.chars);
}
}
Exit:
if (FAILED(hr))
{
wprintf(L"Could not get error string (errorCode=0x%lx)\n", hr);
}
}
//
// Async implementation
//
// 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;
}
}
}
//
// Sync caller
//
void CallAddSync(int a, int b)
{
HRESULT hr;
WS_ERROR* error = NULL;
// Create an error object for storing rich error information
hr = WsCreateError(
NULL,
0,
&error);
if (FAILED(hr))
{
goto Exit;
}
int sum;
hr = Add(a, b, &sum, NULL, error);
if (FAILED(hr))
{
goto Exit;
}
wprintf(L"%d\n", sum);
Exit:
if (FAILED(hr))
{
// Print out the error
PrintError(hr, error);
}
fflush(
stdout);
if (error != NULL)
{
WsFreeError(error);
}
}
//
// Async caller
//
// Used to store state used to synchronize between callback and main thread
struct AddCompletion
{
HANDLE eventHandle;
HRESULT errorCode;
};
// WS_ASYNC_CALLBACK that is called when add completes asynchronously
void CALLBACK OnAddComplete(HRESULT hr, WS_CALLBACK_MODEL callbackModel, void* callbackState)
{
UNREFERENCED_PARAMETER(callbackModel);
// Get the callback state
AddCompletion* addCompletion = (AddCompletion*)callbackState;
// Store the HRESULT
addCompletion->errorCode = hr;
// Since we just set an event, we are ok with a callbackModel of WS_SHORT_CALLBACK or WS_LONG_CALLBACK
// Signal main thread that the operation is complete
SetEvent(addCompletion->eventHandle);
}
void CallAddAsync(int a, int b)
{
HRESULT hr;
WS_ERROR* error = NULL;
HANDLE eventHandle = NULL;
int* sumPointer = NULL;
// Create an error object for storing rich error information
hr = WsCreateError(
NULL,
0,
&error);
if (FAILED(hr))
{
goto Exit;
}
// Create an event handle that will be signaled in callback
eventHandle = CreateEvent(NULL, FALSE, FALSE, NULL);
if (eventHandle == NULL)
{
hr = HRESULT_FROM_WIN32(GetLastError());
goto Exit;
}
// Store information used by the callback when add completes
AddCompletion addCompletion;
addCompletion.eventHandle = eventHandle;
// Allocate space to store return value
sumPointer = (int*)HeapAlloc(GetProcessHeap(), 0, sizeof(int));
if (sumPointer == NULL)
{
hr = E_OUTOFMEMORY;
goto Exit;
}
// Specify the callback to call if function completes synchronously
// along with the state to pass to the callback (AddCompletion structure)
WS_ASYNC_CONTEXT asyncContext;
asyncContext.callback = OnAddComplete;
asyncContext.callbackState = &addCompletion;
// Call the function asynchronously
hr = Add(a, b, sumPointer, &asyncContext, error);
// Zero out asyncContext to illustrate that async function should have copied it
ZeroMemory(&asyncContext, sizeof(asyncContext));
if (hr == WS_S_ASYNC)
{
// Function completed asynchronously
// Wait for callback to signal completion
if (WaitForSingleObject(eventHandle, INFINITE) != WAIT_OBJECT_0)
{
hr = HRESULT_FROM_WIN32(GetLastError());
goto Exit;
}
// Get error code that was stored by callback
hr = addCompletion.errorCode;
}
wprintf(L"%d\n", *sumPointer);
Exit:
if (FAILED(hr))
{
// Print out the error
PrintError(hr, error);
}
fflush(
stdout);
if (eventHandle != NULL)
{
CloseHandle(eventHandle);
}
if (sumPointer != NULL)
{
// Free value
HeapFree(GetProcessHeap(), 0, sumPointer);
}
if (error != NULL)
{
WsFreeError(error);
}
}
// Main entry point
int __cdecl wmain(int argc, __in_ecount(argc) wchar_t **argv)
{
UNREFERENCED_PARAMETER(argc);
UNREFERENCED_PARAMETER(argv);
CallAddSync(0, 0);
CallAddSync(1, 2);
CallAddAsync(0, 0);
CallAddAsync(1, 2);
return 0;
}