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A Per-Thread Singleton Class

May 2002/A Per-Thread Singleton Class/Listing 1

Listing 1: Per-thread Singleton class implementation

#include <windows.h>
#include <iostream.h>

// This class ensures that the thread specific instance gets 
// deleted as each thread exits.
class ThreadSingletonDestroyer

// This class implements the functionality needed for a thread
// specific Singleton class.
class ThreadSingleton
    static ThreadSingleton* GetObject();
    DWORD GetThreadID()
        return m_ThreadID;

    ThreadSingleton(DWORD threadID)
        m_ThreadID = threadID;

    static DWORD m_ThreadIndex;
    DWORD  m_ThreadID;
    static void DestroyObject();

    friend ThreadSingletonDestroyer;

DWORD ThreadSingleton :: m_ThreadIndex = -1;

ThreadSingletonDestroyer :: ~ThreadSingletonDestroyer()
    // Just call the function DestroyObject.
    ThreadSingleton :: DestroyObject();

void ThreadSingleton :: DestroyObject()
    // If the thread Index is not even initialized yet, it 
    // means there have been no object created for this class 
    // yet, just return.
    if(-1 == m_ThreadIndex)

    ThreadSingleton *obj = NULL;

    // If there is an object at the TLS index, delete it, 
    // otherwise just return.
    obj = (ThreadSingleton*)TlsGetValue(m_ThreadIndex);

    if(NULL != obj)
        delete obj;

ThreadSingleton* ThreadSingleton :: GetObject()
    ThreadSingleton *retVal = NULL;

    // This "if" block needs to be protected by a 
    // CRITICAL_SECTION, left out for sake of clarity.
    if(-1 == m_ThreadIndex)
        m_ThreadIndex = TlsAlloc();
        if(-1 == m_ThreadIndex)
            cout << "Error while calling TlsAlloc\n";
            return NULL;

    // Try to get an object at the TLS index, but if we can't 
    // then create one and put in the TLS location.
    retVal = (ThreadSingleton*)TlsGetValue(m_ThreadIndex);

    if(NULL == retVal)
        retVal = new ThreadSingleton(GetCurrentThreadId());
        TlsSetValue(m_ThreadIndex, retVal);

    return retVal;

// This is the thread function, this function is called to 
// execute the thread created in "main".
DWORD WINAPI ThreadMain(void*)
    // This object's destructor will destroy the thread 
    // specific singleton instance, upon the thread's exit.
    ThreadSingletonDestroyer tsDestroyer;

    ThreadSingleton *obj = ThreadSingleton :: GetObject();

    cout <<"The thread ID is = " << obj->GetThreadID() << endl;

    return 0;

int main()
    ThreadSingletonDestroyer tsDestroyer;
    DWORD dwThreadID;

    ThreadSingleton *obj = ThreadSingleton :: GetObject();

    // Print the thread ID.
    cout <<"The thread ID is = " << obj->GetThreadID() << endl;

    HANDLE handle = CreateThread(NULL, 0, ThreadMain, NULL, 0, 

    if(NULL == handle)
        cout << "Error while creating a thread!\n";
        return -1;

    (void)WaitForSingleObject(handle, INFINITE);

    return 0;
— End of Listing —

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