Does Anyone Understand Semaphores?

[reliv1908]

I have a project in my C++ class that I've been having some trouble with. I don't fully understand semaphores, and this particular problem revolves around semaphores. The given code is:

// project4.cpp : main project file.

#include "stdafx.h"

using namespace System;
using namespace System::Threading;

ref class PrintTasks
{
private:
	static Semaphore ^canPrintA = gcnew Semaphore(1, 1);
	static Semaphore ^canPrintB = gcnew Semaphore(0, 1);
	static Semaphore ^canPrintC = gcnew Semaphore(0, 1);

public: static bool runFlag = true;

public:
	void PrintA(Object^ name) {
	    while (runFlag) {
                        canPrintA->WaitOne();
			Console::Write("{0}\n", "A");
                        canPrintB->Release();
		}
	}

	void PrintB(Object^ name) {
	    while (runFlag) {
                        canPrintB->WaitOne();
			Console::Write("{0}\n", "B");
                        canPrintC->Release();
		}
	}

	void PrintC(Object^ name) {
	    while (runFlag) {
                        canPrintC->WaitOne();
			Console::Write("{0}\n", "C");
                        canPrintA->Release();
		}
	}
};

int main(array<System::String ^> ^args)
{

	PrintTasks ^tasks = gcnew PrintTasks();

	// First Method
	Thread ^thread1 = gcnew Thread ( gcnew ParameterizedThreadStart( tasks, &PrintTasks::PrintA ) );
	Thread ^thread2 = gcnew Thread ( gcnew ParameterizedThreadStart( tasks, &PrintTasks::PrintB ) );
	Thread ^thread3 = gcnew Thread ( gcnew ParameterizedThreadStart( tasks, &PrintTasks::PrintC ) );

	thread1->Start("printA");
	thread2->Start("printB");
	thread3->Start("printC");

	Thread::Sleep(50);

	PrintTasks::runFlag=false;

	thread3->Abort();
	thread2->Abort();
	thread1->Abort();

	return 0;
}

I have written it so that this will continuously print A on one line, B on the next, C on the next, A, B, C, and so on. The goal is to write ONLY semaphore-related statements (no control structure, no added print statements, no nothing) to print AAA on one line, BB on the next, and C on the next, for the pattern AAA, BB, C, AAA, BB, C, AAA, BB, C. Any suggestions on how to make the A part print three times and the B part twice, by only adding/deleting/editing semaphore stuff?

[reliv1908]

I got it.

[kev82]

I don't recognise the language (C++/CLI?) but to get AAA on one line, you're surely going to have to modify a print statement, because you only have one print statement with an `A`, and from my understanding, it prints a newline after every `A'.

[Azagaros]

The code presented isn't c++. Is it c#? Thread ^thread isn't c++, it looks like a object pascal hybrid. C++ would look like Thread *thread = new Thread( constructor params); .

[1yR4jE8b]

It's C++/CLI --- not generally accepted on this forum. Not many people know it, or care to learn it because it is not standard at all.