c++ 知识点 ： 线程相关
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1、线程开始事件、线程结束事件、WaitForMultipleObjects 控制线程
假如线程是无限循环的，需要从线程外部控制线程结束
//用于线程管理的两事件
//HANDLE CreateEventA(
// LPSECURITY_ATTRIBUTES lpEventAttributes,
// BOOL bManualReset,
// BOOL bInitialState,
// LPCSTR lpName
// );
// create a "loopback capture has started" event
HANDLE hStartedEvent = CreateEvent(NULL, FALSE, FALSE, NULL);
if (NULL == hStartedEvent) {
printf("CreateEvent failed: last error is %u\n", GetLastError());
return -__LINE__;
}
// create a "stop capturing now" event
HANDLE hStopEvent = CreateEvent(NULL, FALSE, FALSE, NULL);
if (NULL == hStopEvent) {
printf("CreateEvent failed: last error is %u\n", GetLastError());
CloseHandle(hStartedEvent);
return -__LINE__;
}
AI助手创建线程
将事件作为参数传入线程
// create arguments for loopback capture thread
LoopbackCaptureThreadFunctionArguments threadArgs;
threadArgs.hr = E_UNEXPECTED; // thread will overwrite this
threadArgs.pMMDevice = prefs.m_pMMDevice;
threadArgs.bInt16 = prefs.m_bInt16;
threadArgs.hStartedEvent = hStartedEvent; //将这两个事件作为参数，传入线程
threadArgs.hStopEvent = hStopEvent; //
threadArgs.nFrames = 0;
threadArgs.bMono = prefs.m_bMono;
threadArgs.iSampleRateDivisor = prefs.m_iSampleRateDivisor;
AI助手 //创建线程
HANDLE hThread = CreateThread(
NULL, 0,
LoopbackCaptureThreadFunction, &threadArgs,
0, NULL
);
if (NULL == hThread) {
printf("CreateThread failed: last error is %u\n", GetLastError());
CloseHandle(hStopEvent);
CloseHandle(hStartedEvent);
return -__LINE__;
}
AI助手线程内部处理：预处理过程、无限循环过程
hr = pAudioClient->Start();
if (FAILED(hr)) {
printf("IAudioClient::Start failed: hr = 0x%08x\n", hr);
AvRevertMmThreadCharacteristics(hTask);
pAudioCaptureClient->Release();
CloseHandle(hWakeUp);
pAudioClient->Release();
return hr;
}
//预处理结束，通知主线程，此时主线程使用WaitForMultipleObjects 等待
SetEvent(hStartedEvent);
// loopback capture loop
HANDLE waitArray[2] = { hStopEvent, hWakeUp };
DWORD dwWaitResult;
//循环阶段
bool bDone = false;
for (UINT32 nPasses = 0; !bDone; nPasses++)
AI助手主线程序依赖于调用该函数来分析出当前状态
DWORD WaitForMultipleObjects(
DWORD nCount, // 句柄的数量 最大值为MAXIMUM_WAIT_OBJECTS（64）
CONST HANDLE* lpHandles, //句柄数组的指针
BOOL fWaitAll, //等待所有事件有信号，还是只要一个有信号就返回
DWORD dwMilliseconds //超时时间 超时后向执行。 如果为INFINITE 永不超时。如果没有信号量就会在这死等。
);
AI助手This function indicates a value when either one of the specified objects is in the signaling state, or the timeout interval reaches its timeout limit.
当WaitForMultipleObjects()等到多个内核对象的时候，
如果它的bWaitAll 参数设置为false
其返回值
等于 WAIT_OBJECT_0 + lpHandles数组的序号（从0开始计数）
如果，多个都有内核被同时触发，有信号，则返回其中序号最小的那个。
判断： 主线程 判断 子线程 是否预处理成功
//等待事件开始，或者线程结束
// wait for either capture to start or the thread to end
HANDLE waitArray[2] = { hStartedEvent, hThread };
DWORD dwWaitResult;
dwWaitResult = WaitForMultipleObjects(
ARRAYSIZE(waitArray), waitArray,
FALSE, INFINITE
);
//线程结束了，但此时hStartedEvent还没有信号，说明线程在初始化阶段 失败了
if (WAIT_OBJECT_0 + 1 == dwWaitResult) {
printf("Thread aborted before starting to loopback capture: hr = 0x%08x\n", threadArgs.hr);
CloseHandle(hStartedEvent);
CloseHandle(hThread);
CloseHandle(hStopEvent);
return -__LINE__;
}
//未预期的错误
if (WAIT_OBJECT_0 != dwWaitResult) {
printf("Unexpected WaitForMultipleObjects return value %u", dwWaitResult);
CloseHandle(hStartedEvent);
CloseHandle(hThread);
CloseHandle(hStopEvent);
return -__LINE__;
}
//线程初始化成功，关闭开始事件，线程执行无限循环阶段
CloseHandle(hStartedEvent);
AI助手结束： 主线程结束子线程
将结束事件设置为有信号
SetEvent(hStopEvent);
子线程在循环过程中，要判断结束事件是否有信号，有则结束
HANDLE waitArray[2] = { hStopEvent, hWakeUp };
//子线程在循环过程中判断
dwWaitResult = WaitForMultipleObjects(
ARRAYSIZE(waitArray), waitArray,
FALSE, INFINITE
);
//主线程将结束事件设置为有信号，子线程循环过程中判断 若有信号，则结束循环
if (WAIT_OBJECT_0 == dwWaitResult) {
printf("Received stop event after %u passes and %u frames\n", nPasses, *pnFrames);
bDone = true;
continue; // exits loop
}
AI助手2 结束进程
在某些情况下，在某些特定场景下（如未完成的任务或异常中断时），常规处理流程未能完成当前任务。此时可通过强行终止进程的操作来完成当前任务的处理。
BOOL KillProcessFromPidT(int nPid)
{
DWORD dwProcessID = nPid;
HANDLE hProcess = ::OpenProcess(PROCESS_TERMINATE, FALSE, dwProcessID);
::TerminateProcess(hProcess, 0);
CloseHandle(hProcess);
return true;
}
AI助手 int nPid = _getpid();
KillProcessFromPidT(nPid);
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