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C++ Programming : Threads

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What are threads?

Simple explanation of threads is - when u open any application such as Internet Explorer, a process is created. For IE it is IExplorer.exe, but in reality, a process is divided into multiple units of process, such units are called threads. When u open Windows Task Manager ,u will see how many threads are running for each process. Right now for IE, i can see 17 threads.

It is important for C/C++ programmer to know what threads are and how they work. Following a C++ class for creating and terminating threads.

 

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//thread.h

#include <windows.h>

#include <process.h>

#include <assert.h>

//Class CThread

class CThread

{

public:

CThread( int nPriority = THREAD_PRIORITY_NORMAL );

bool WaitUntilTerminate( DWORD dwMilliSec = INFINITE );

bool Start();

bool Pause();

bool IsRunning();

bool IsTerminated();

bool IsSuspend();

void SetPriority( int nLevel );

int GetPriority();

void Terminate();

public:

virtual void OnInitInstance(){}//main initialization code

virtual void OnRunning() = 0;

virtual DWORD OnExitInstance() { return 0;}//clean up

static unsigned __stdcall ThreadProc( LPVOID param );

virtual ~CThread(){

::CloseHandle( m_hEvent );

}

public:

HANDLE m_hThread, m_hEvent;

int m_nPriority;

unsigned long m_dwThreadID;

bool m_bTerminate, m_bSuspend, m_bIsRunning;

 

};

 

//Implementation

CThread::CThread( int nPriority )

{

m_nPriority = nPriority;

m_hThread = NULL;

m_dwThreadID = 0;

m_bTerminate = true;

m_bSuspend = true;

m_bIsRunning = false;

m_hEvent = ::CreateEvent( NULL, FALSE, FALSE, NULL );

}

bool CThread::WaitUntilTerminate( DWORD dwMilliSec )

{

if( m_dwThreadID == 0 ) return false;

if( ::WaitForSingleObject( m_hThread, dwMilliSec ) == WAIT_TIMEOUT ){

return false;

}

m_bIsRunning = false;

m_bTerminate = true;

return true;

}

 

bool CThread::Start()

{

if( m_bTerminate ){

m_hThread = (HANDLE)CreateThread( NULL, 0, (unsigned long ( __stdcall*)(void*))ThreadProc, (void*)this,0, &m_dwThreadID );

if( m_hThread == 0 ){

return false;

}

else {

::SetEvent( m_hEvent );

m_bIsRunning = true;

return true;

}

}

return true;

}

bool CThread::Pause()

{

if( m_bTerminate ) return false;

if( m_bSuspend ) return true;

DWORD nRet = ::SuspendThread(m_hThread);

if(nRet == 0xFFFFFFFF) return false;

m_bSuspend = true;

return true;

}

bool CThread::IsRunning()

{

return m_bIsRunning;

}

 

bool CThread::IsTerminated()

{

return m_bTerminate;

}

 

 

bool CThread::IsSuspend()

{

return m_bSuspend;

}

 

void CThread::SetPriority( int nLevel )

{

SetThreadPriority( m_hThread, nLevel );

}

 

int CThread::GetPriority()

{

return GetThreadPriority( m_hThread );

}

void CThread::Terminate()

{

DWORD dwExitCode;

::GetExitCodeThread( m_hThread, &dwExitCode );

if( dwExitCode == STILL_ACTIVE ){

::TerminateThread( m_hThread, dwExitCode );

::CloseHandle( m_hThread);

m_hThread = NULL;

}

m_bTerminate = true;

m_bIsRunning = false;

 

}

unsigned __stdcall CThread::ThreadProc( LPVOID param )

{

CThread* pThread = reinterpret_cast<CThread*>(param);

pThread->SetPriority( pThread->m_nPriority );

pThread->m_bIsRunning = true;

::SetEvent( pThread->m_hEvent );

pThread->OnInitInstance();

pThread->OnRunning();

return pThread->OnExitInstance();

 

}

 

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