Question

i have a simple C program that uses CRITICAL_SECTION.
for some reason it seem to enter the CRITICAL_SECTION again and again and not really execute the code inside, causing the threads to deadlocked.
i cannot seem to find the reason for this.

here is the code:

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

#define N 100000000

CRITICAL_SECTION cs;

static DWORD WINAPI safe_increment(void *param)
{
   volatile long* x = (volatile long*)param;
   for(int i=0;i<N;++i)
      EnterCriticalSection(&cs);
      ++(*x);
      LeaveCriticalSection(&cs);
   return 0;
}

void main()
{
   InitializeCriticalSection(&cs);

  volatile long x = 0;

  HANDLE h[2];
  DWORD thread_id;

   int x = 0;

   h[0] = CreateThread(NULL,0,safe_increment,(void*)&x,0,&thread_id);
   h[1] = CreateThread(NULL,0,safe_increment,(void*)&x,0,&thread_id);
   WaitForMultipleObjects(2,h,TRUE,INFINITE);
   CloseHandle(h[0]);
   CloseHandle(h[1]);

   DeleteCriticalSection(&cs);

   std::cout << "Result of safe increment: " << x << "\n";
}

thank you!

Roy.

Answer 1

Mistake in for loop. Should be:

for(int i=0;i<N;++i)
{ // <---
      EnterCriticalSection(&cs);
      ++(*x);
      LeaveCriticalSection(&cs);
} // <---

No braces so the for loop only executed EnterCriticalSection() and nothing else. The first thread that acquired the critical section never released it: deadlock.