Multithreading problem

YellowFish · #1 22-Jul-2004, 05:58

I am running a multi threaded program, and it seems like the threads simply don't run.
Here is a short summary of my code (changed the names of classes and cut off unnecessary code):

these are files from Core.dll project

CPP / C++ / C Code:

// CCore.h
class CCore
{
public:
	CCore();
	~CCore();
// the Init receives pointers to 2 thread-safe queues
	void	Init(CSynQueue* pSendQ, CSynQueue* pRecvQ);
	void	Term();
private:
	HANDLE		m_hSendThreadHandle;
	HANDLE		m_hRecvThreadHandle;
	DWORD		m_pSendThreadID;
	DWORD		m_pRecvThreadID;
	CRITICAL_SECTION	m_CriticalSection;
	bool		m_bSendActive;
	bool		m_bRecvActive;

	void	StartThreads();
	void	EndThreads();
	void	Sender();
	void	Receiver();
	friend DWORD WINAPI	SendThreadFunc(void* Obj);
	friend DWORD WINAPI	RecvThreadFunc(void* Obj);
};


// CCore.cpp

// global functions - these functions are passed to CreateThread as the start
// address where each thread runs

DWORD WINAPI SendThreadFunc(void* Obj)
{
	printf("SENDER THREAD FUNC STARTED\n");
	((Cm104Core*)Obj)->Sender();
	ExitThread(0);
	return 0;
}


DWORD WINAPI RecvThreadFunc(void* Obj)
{
	printf("RECEIVER THREAD FUNC STARTED\n");
	((Cm104Core*)Obj)->Receiver();
	ExitThread(0);
	return 0;
}


void	CCore::Init(CSynQueue* pSendQ, CSynQueue* pRecvQ)
{
// do all sorts of stuff here
// then call:
StartThreads();
}

void CCore::StartThreads()
{
	m_bSendActive = m_bRecvActive = true;
	m_hSendThreadHandle = CreateThread(NULL, 0, SendThreadFunc, this, 0, &m_pSendThreadID);
	m_hRecvThreadHandle = CreateThread(NULL, 0, RecvThreadFunc, this, 0, &m_pRecvThreadID);
}



void CCore::EndThreads()
{
	m_bSendActive = m_bRecvActive = false;
}

void CCore::Sender()
{
while(m_bSendActive )
{
    // do something here
}
}

void CCore::Receiver()
{
while(m_bRecvActive )
{
    // do something here
}
}

in my exe project (lets call it myEXE.exe) i have this file:

CPP / C++ / C Code:

// main.cpp

class CCore* pCore = new CCore;
pCore->Init()
// etc

The problem is that the threads don't seem to run (i never get the line "SENDER THREAD FUNC STARTED" or "RECEIVER THREAD FUNC STARTED").
Any ideas?

YellowFish · #2 22-Jul-2004, 06:32

it seems like the threads exit right after they start, while debugging i get

Quote:

The thread 0x804 has exited with code 0 (0x0).
The thread 0x934 has exited with code 0 (0x0).

right after i call -
StartThreads();

RonBurk · #3 23-Jul-2004, 03:11

printf() would not be my first choice of an output debugging function for a thread created by CreateThread(). I would switch to OutputDebugString(). I would also make sure that main thread waits on the threads it creates to complete before exiting.

YellowFish · #4 25-Jul-2004, 05:11

Quote:

Originally Posted by RonBurk

I would also make sure that main thread waits on the threads it creates to complete before exiting.

That was my problem, Instead of doing something like

CPP / C++ / C Code:

while
{
getchar() ! = 'q';
}

or just a

CPP / C++ / C Code:

Sleep(MY_TIME)

after calling create threads,
I used a breakpoint, apparantly taht wasn't enough.
Thanx

dsmith · #5 25-Jul-2004, 08:00

I am using posix threads, but I think they are really similar to the windows threads that you are using. What I have noticed is that if I treat the main function as a thread as well (by calling pthread_exit) in main, it will wait for the other threads to finish.

Example:

CPP / C++ / C Code:

#include "pthread.h"

void* function1()
{
	sleep(1);
	printf("Function 1 called.\n");
	pthread_exit(NULL);
}

void* function2()
{
	sleep(2);
	printf("Function 2 called.\n");
	pthread_exit(NULL);
}


int main(){
	pthread_t	thread1;
	pthread_t	thread2;
	
	pthread_create(&thread1,0,function1,0);
	pthread_create(&thread2,0,function2,0);
	pthread_exit(NULL);
	return 0;
}

This will pause 1 second and print "Function 1 called", pause another second and print "Function 2 called", even though the flow control in main runs through to the end. I would be curious to see if the same is true with the windows threads that you are using.

YellowFish · #6 26-Jul-2004, 02:36

nice idea dsmith, just tryied it out and your idea works also in windows (using win API function - "ExitThread(0)" ).
chhers

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