A C++ multi thread safe singleton example with source code has been posted

(Last Updated On: June 15, 2010)

Lock.h

//Example from http://www.relisoft.com/Win32/active.html
#if !defined _LOCK_H_
#define _LOCK_H_

#include “Mutex.h”

class Lock
{
public:
// Acquire the state of the semaphore
Lock ( Mutex & mutex )
: _mutex(mutex)
{
_mutex.Acquire();
}
// Release the state of the semaphore
~Lock ()
{
_mutex.Release();
}
private:
Mutex & _mutex;
};

#endif

Mutex.h

//Example from http://www.relisoft.com/Win32/active.html
#if !defined _MUTEX_H_
#define _MUTEX_H_

class Mutex
{
friend class Lock;
public:
Mutex () { InitializeCriticalSection (& _critSection); }
~Mutex () { DeleteCriticalSection (& _critSection); }
private:
void Acquire ()
{
EnterCriticalSection (& _critSection);
}
void Release ()
{
LeaveCriticalSection (& _critSection);
}

CRITICAL_SECTION _critSection;
};

#endif

Singleton.h

#include “Lock.h”
#include “Mutex.h”

class aSingletonClass
{
public:
//method to get Instance of class
static aSingletonClass *getInstance( void )
{
//Note that the class is only created when this method is called first time
if(!instance_)
instance_ = new aSingletonClass;
return instance_;
}
//method to delete Instance of class
static void deleteInstance( void )
{
if(instance_)
delete instance_;
instance_ = NULL; //important as this can create dead reference problems
}
void printSomething(char *name, int count)
{
Lock guard(mutex_);
std::cout << name << " loop " << count << std::endl; } private: //variable to store the instance of singleton static aSingletonClass *instance_; //default constructor should be private to prevent instantiation aSingletonClass() {}; //destructor should be made private so no one can delete this accidently ~aSingletonClass() {}; //We also need to prevent copy being created of the object aSingletonClass(const aSingletonClass&); Mutex mutex_; }; Thread.cpp //Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy //This shows example of Multithreading, thread sync, Mutex #include
#include #include
#include “Singleton.h”

using namespace std;

aSingletonClass* aSingletonClass::instance_ = NULL;

void Func1(void *);
void Func2(void *);

int main()
{
HANDLE hThreads[2];

aSingletonClass *someVar = NULL;
//Create Instance
someVar = aSingletonClass::getInstance();

//Create two threads and start them
hThreads[0] = (HANDLE)_beginthread(Func1, 0, NULL);
hThreads[1] = (HANDLE)_beginthread(Func2, 0, NULL);

//Makes sure that both the threads have finished before going further
WaitForMultipleObjects(2, hThreads, TRUE, INFINITE);

cout << "Main exit" << endl; return 0; } void Func1(void *P) { int Count; for (Count = 1; Count < 11; Count++) { aSingletonClass::getInstance()->printSomething(“Func1”, Count);
}
return;
}

void Func2(void *P)
{
int Count;

for (Count = 10; Count > 0; Count–)
{
aSingletonClass::getInstance()->printSomething(“Func2”, Count);
}
return;
}

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