Thread: Multithreading

I am making an application wherein on clicking a button, a thread is created if its not already created. If the thread is already created then the current instance of the thread is deleted and the new instance of the thread is created. Now my problem is that i am not able to check if the thread is already active and how to kill that thread from the main thread.

something of my own...
For windows there's the WaitForSingleObject function..
for linux.. I asked that question like.. 4 days ago, and CodePlug told me to use the pthread_cleanup_push... which basicly I emulated...
This code is incomplete.. only serves as example.
First there's the header then the body

Code:

#ifdef WIN32
	#include<windows.h>
	
	typedef DWORD THREADRETTYPE;
	typedef DWORD pthread_t;

	typedef struct _THREAD_ATTRS{
		int n_refs;
		pthread_t thread_id;
		HANDLE hwthread;
		DWORD  (WINAPI *func)(void*);
	} THREAD_ATTRS;

#else
	#include <pthread.h>
	#define WINAPI

	typedef struct _THREAD_ATTRS{
		int n_refs;
		pthread_t thread_id;
		void* (*func)(void*);
		bool ended;
	} THREAD_ATTRS;

	typedef void* THREADRETTYPE;

#endif

typedef THREADRETTYPE  (WINAPI *THREADCALLBACKFUNC)(void*);
class Thread{
private:
#ifndef WIN32	
	friend void* pthread_entry_func(void*);
#endif
	THREAD_ATTRS *attrs;
public:
	Thread(THREADCALLBACKFUNC = NULL);
	Thread(const Thread&);
	~Thread();

	Thread& operator=(const Thread&);

	pthread_t id();
	bool run(void *args);
	bool isRunning();
	bool hasExited();
	bool waitExit(THREADRETTYPE* retval=NULL);
	bool terminate();

};

and the cpp you need

Code:

#ifndef WIN32
struct pthread_args{
	Thread *thread;
	void *args;
	void *(*f)(void*);
};

void* pthread_entry_func(void* args){
	pthread_args* p = (pthread_args*)args;
	
	Thread& t = *p->thread;
	THREADCALLBACKFUNC f = p->f;
	void *params = p->args;
	
	delete p;
	
	if(t.attrs) t.attrs->ended=false;
	void *res=NULL;
	try{
		res = f(params);
	}catch(...){
		if(t.attrs)	t.attrs->ended=true;
		throw;
	}
	if(t.attrs)	t.attrs->ended=true;	
	return res;
}

#endif

bool Thread::run(void *args){
	assert(attrs != NULL);
	if(isRunning() || attrs->func == NULL )
		return false;
#ifdef WIN32
	attrs->hwthread = CreateThread(NULL,0,attrs->func,args,0,&attrs->thread_id);
	return attrs->hwthread!=NULL;
#else
	pthread_args *p = new pthread_args;
	p->thread=this;	
	p->f=attrs->func;	
	p->args=args;	
	
	return pthread_create(&attrs->thread_id,NULL,pthread_entry_func,p) == 0;
#endif
}

bool Thread::hasExited(){
	if(attrs == NULL) return true;
#ifdef WIN32
	bool res = WaitForSingleObject(attrs->hwthread,0) == WAIT_OBJECT_0;
#else
	bool res = attrs->ended;
#endif
	if(res)
		clean_THREAD_ATTRS(attrs);
	return res;
}

bool Thread::terminate(){
#ifdef WIN32
	bool ret = TerminateThread(attrs->hwthread,1)==TRUE;
#else
	bool ret = pthread_cancel(attrs->thread_id)==0;
#endif
	clean_THREAD_ATTRS(attrs);
	return ret;
}

Originally Posted by Salem

Which version of "threads" are you using for which OS and Compiler?

I am using MFC threads in Windows XP and Visual Studio 6.0

I am using MFC threads in Windows XP and Visual Studio 6.0

Worker threads or user interface threads? Anyway, you'll probably will use some state variable that will tell whether the thread has initialized or has exited. It'll have to be protected by using CSingleLock and a CCriticalSection. I don't know, hoiwever, if you actually need to be destroying your thread and then recreating it. You might just want to switch the direction of the processing going on in this thread.

The proper way to check if a thread is running is to call one of the wait functions using the thread handle. If the thread handle is "signaled", then it is running.

Here's a thread object you can use in your MFC apps. It's much betting than CWinThread.

http://cboard.cprogramming.com/showthread.php?t=66229

gg