I am trying to solve the dining philosophers problem.
In my case, every philosopher should eat 1,000,000 times. The problem is that it seems like only "1" and is "3" finished eating. I am using threads with critical section lock, here is my code:
CRITICAL_SECTION ghCARITICALSection1;
CRITICAL_SECTION ghCARITICALSection2;
CRITICAL_SECTION ghCARITICALSection3;
CRITICAL_SECTION ghCARITICALSection4;
CRITICAL_SECTION ghCARITICALSection5;
DWORD WINAPI func(int* phiphilosopher)
{
if (1 == *phiphilosopher && TryEnterCriticalSection(&ghCARITICALSection1) && TryEnterCriticalSection(&ghCARITICALSection2))
{
std::cout << "1 is eating...\n";
for (int i = 0; i < 1000000; i++)
{
i = i;
}
LeaveCriticalSection(&ghCARITICALSection1);
LeaveCriticalSection(&ghCARITICALSection2);
}
if (2 == *phiphilosopher && TryEnterCriticalSection(&ghCARITICALSection2) && TryEnterCriticalSection(&ghCARITICALSection3))
{
std::cout << "2 is eating...\n";
for (int i = 0; i < 1000000; i++)
{
}
LeaveCriticalSection(&ghCARITICALSection2);
LeaveCriticalSection(&ghCARITICALSection3);
}
if (3 == *phiphilosopher && TryEnterCriticalSection(&ghCARITICALSection3) && TryEnterCriticalSection(&ghCARITICALSection4))
{
std::cout << "3 is eating...\n";
for (int i = 0; i < 1000000; i++)
{
}
LeaveCriticalSection(&ghCARITICALSection3);
LeaveCriticalSection(&ghCARITICALSection4);
}
//...also for 4,5
return 0;
}
int philosopher1 = 1;
int* philosopher1ptr = &philosopher1;
int philosopher2 = 2;
int* philosopher2ptr = &philosopher2;
//...Also for philosopher 3,4,5
InitializeCriticalSection(&ghCARITICALSection1);
InitializeCriticalSection(&ghCARITICALSection2);
//...aslo for ghCARITICALSection 3,4,5
HANDLE WINAPI th1 = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)func, philosopher1ptr, 0, NULL);
HANDLE WINAPI th2 = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)func, philosopher2ptr, 0, NULL);
////...aslo for th3,4,5
WaitForSingleObject(th1, INFINITE);
WaitForSingleObject(th2, INFINITE);
//...also for th3,4,5
Think about the logic here
if (TryEnterCriticalSection(&a) && TryEnterCriticalSection(&b)) {
// . . .
LeaveCriticalSection(&a);
LeaveCriticalSection(&b);
}
What happens if TryEnterCriticalSection(&a)
succeeds and TryEnterCriticalSection(&b)
fails; the CS a
remains in entered state forever.
It should look something like
if (TryEnterCriticalSection(&a)) {
if (TryEnterCriticalSection(&b)) {
// . . .
LeaveCriticalSection(&b);
}
LeaveCriticalSection(&a);
}