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WebRTC學習之八：函數的異步執行

來源：程序員人生發布時間：2017-02-21 08:30:08 閱讀次數：4784次

WebRTC在asyncinvoker.h和asyncivoker.cpp中實現了函數的異步履行。asyncinvoker.h的注釋中給出了1個小例子，本文的學習就是從這個例子開始的。但是這個例子和單元測試代碼都只演示了如何讓1個函數在子線程中履行，以下所示。

myclass.h

#include "webrtc/base/asyncinvoker.h"
#include <iostream>
#include <memory>

class MyClass 
{

public:
	MyClass();
	void OneTask(rtc::Thread *thread, int x);

	void AnotherAsyncTask(int x);
	
private:
	std::unique_ptr<rtc::AsyncInvoker> invoker;
};

myclass.cpp

#include "myclass.h"
MyClass::MyClass()
{
	invoker.reset(new rtc::AsyncInvoker());
	std::cout << "Main Thread ID:" << rtc::Thread::Current()->GetId() << std::endl;
}

void MyClass::OneTask(rtc::Thread *thread, int x)
{
	invoker->AsyncInvoke<void>(RTC_FROM_HERE, thread, rtc::Bind(&MyClass::AnotherAsyncTask, (MyClass*)this, x));
}
void MyClass::AnotherAsyncTask(int x)
{
	std::cout << "Worker Thread ID:" << rtc::Thread::Current()->GetId() << std::endl;
	std::cout << "Input Value Is:" << x << std::endl;
}

main.cpp

#include "myclass.h"
int main()
{
	std::unique_ptr<rtc::Thread> myThread = rtc::Thread::Create();
	myThread->Start();
	MyClass *myClass = new MyClass;
	myClass->OneTask(myThread.get(), 10);

	Sleep(10000);

    return 0;
}

打印結果

從上圖輸出的線程ID可以看出，函數AnotherAsyncTask是在子線程中履行的。

但是如何在子線程中調用1個函數，并讓該函數中主線程中履行呢，可以將上述代碼稍作更改，以下所示。

myclass.h

#include "webrtc/base/asyncinvoker.h"
#include <iostream>
#include <memory>

class MyClass 
{

public:
	MyClass();
	void OneTask(rtc::Thread *thread, int x);

	void AnotherAsyncTask(int x);
	
	void myFunction(int x);
	
private:
	std::unique_ptr<rtc::AsyncInvoker> invoker;
	rtc::Thread *mainThread;
};

myclass.cpp

#include "myclass.h"
MyClass::MyClass()
{
	invoker.reset(new rtc::AsyncInvoker());
	std::cout << "Main Thread ID:" << rtc::Thread::Current()->GetId() << std::endl;
	mainThread = rtc::Thread::Current();
}

void MyClass::OneTask(rtc::Thread *thread, int x)
{
	invoker->AsyncInvoke<void>(RTC_FROM_HERE, thread, rtc::Bind(&MyClass::AnotherAsyncTask, (MyClass*)this, x));
}
void MyClass::AnotherAsyncTask(int x)
{
	std::cout << "Worker Thread ID:" << rtc::Thread::Current()->GetId() << std::endl;
	std::cout << "Input Value Is:" << x << std::endl;

	invoker->AsyncInvoke<void>(RTC_FROM_HERE, mainThread, rtc::Bind(&MyClass::myFunction, (MyClass*)this, x));
}

void MyClass::myFunction(int x)
{
	std::cout << "myFunction Thread ID:" << rtc::Thread::Current()->GetId() << std::endl;
	std::cout << "myFunction Value Is:" << x << std::endl;
}

main.cpp

#include "myclass.h"
int main()
{
	std::unique_ptr<rtc::Thread> myThread = rtc::Thread::Create();
	myThread->Start();
	MyClass *myClass = new MyClass;
	myClass->OneTask(myThread.get(), 10);
	
	Sleep(10000);

    return 0;
}

函數AnotherAsyncTask中的invoker->AsyncInvoke<void>(RTC_FROM_HERE, mainThread, rtc::Bind(&MyClass::myFunction, (MyClass*)this, x));是想在mainThread中履行myFunction，但是myFunction并未履行，打印結果仍然和上圖相同。

這里需要將main.cpp稍作修改，添加代碼實現線程的消息循環，新的main.cpp以下所示。

#include "myclass.h"
int main()
{
	std::unique_ptr<rtc::Thread> myThread = rtc::Thread::Create();
	myThread->Start();
	MyClass *myClass = new MyClass;
	myClass->OneTask(myThread.get(), 10);
	
	while (true)
	{
		rtc::Thread::Current()->ProcessMessages(0);
		rtc::Thread::Current()->SleepMs(1);
	}

    return 0;
}

打印結果以下圖所示。