Sleep Command is not working in sub threads - c++

Question

I'm trying to get my Main Program to start a thread that manages a section of my program... The thread that gets made creates a sub thread for each element of an array. The sub thread sets the array element to not available, delays by 10 seconds, and then sets the element to available. The main thread, however, continues normal execution until the array element is available.
However, it doesn't seem to apply a delay...
Please note the array is a global array.
What am I doing wrong?
The below code will outline what I want better then the explanation...
DWORD WINAPI SubThread(void* lpParam)
{
int i = (int)lpParam;
printf("Sub Thread Ran");
structureArray[i].available= false;
Sleep(10000);
structureArray[i].available = true;
return 0;
}
DWORD WINAPI MainThread(void * lpParam)
{
while(true)
{
for(int i = 0; i < structureArray.size(); i++)
{
if(structureArray[i].available)
{
CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)SubThread, (LPVOID)i, 0, NULL);
}
}
}
}

Answer 1

Your global variable is not thread safe, it seems.
Try using a thread safe collection or lock the access yourself (solution is windows specific, inferred from your WINAPI specifier):
class CriticalSection
{
public:
CriticalSection()
{ ::InitializeCriticalSection(&m_cs); }
~CriticalSection()
{ ::DeleteCriticalSection(&m_cs); }
void Enter()
{ ::EnterCriticalSection(&m_cs); }
void Leave()
{ ::LeaveCriticalSection(&m_cs); }
private:
// private to prevent copying
CriticalSection(const CriticalSection&);
CriticalSection& operator=(const CriticalSection&);
CRITICAL_SECTION m_cs;
};
class Lock
{
public:
Lock(CriticalSection& a_section): m_section(a_section)
{ m_section.Enter(); }
~Lock()
{ m_section.Leave(); }
private:
Lock(const CSLock&);
Lock& operator=(const CSLock&);
CriticalSection& m_section;
};
CriticalSection g_dontUseGlobalCS;
DWORD WINAPI SubThread(void* lpParam)
{
int i = (int)lpParam;
printf("Sub Thread runs for...");
Sleep(10000);
{ // use scope to destroy lock...
Lock(g_dontUseGlobalCS);
structureArray[i].available= true;
} // exactly here
// note: a new thread could already be running here
// for debugging purposes add this:
printf("10 seconds.");
return 0;
}
DWORD WINAPI MainThread(void * lpParam)
{
while(true)
{
for(int i = 0; i < structureArray.size(); i++)
{
Lock(g_dontUseGlobalCS);
if(structureArray[i].available)
{
// set the thread availability here
structureArray[i].available = false;
CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)SubThread, (LPVOID)i, 0, NULL);
}
}
}
}
I also moved the set of the availability flag to the creator thread. Usually you would use other mechanisms to realize what you are trying to do:
Look into windows synchronization functions or wiki