Multi-threaded 'fixed'

Question

I have a huge array that is being analyzed differently by two threads:

• Data is large- no copies allowed
• Threads must process concurrently
• Must disable bounds checking for maximum performance

Therefore, each thread looks something like this:

unsafe void Thread(UInt16[] data)
{
  fixed(UInt16* pData = data)
  {
    UInt16* pDataEnd = pData + data.Length;
    for(UInt16* pCur=pData; pCur != pDataEnd; pCur++)
    {
      // do stuff
    }
  }
}

Since there is no mutex (intentionally), I'm wondering if it's safe to use two fixed statements on the same data on parallel threads?? Presumably the second fixed should return the same pointer as the first, because memory is already pinned... and when the first completes, it won't really unpin memory because there is a second fixed() still active.. Has anyone tried this scenario?

Answer 1

Maybe instead of using fixed, you could use GCHandle.Alloc to pin the array:

// not inside your thread, but were you init your shared array
GCHandle handle = GCHandle.Alloc(anArray, GCHandleType.Pinned);
IntPtr intPtr = handle.AddrOfPinnedObject();


// your thread
void Worker(IntPtr pArray)
{
  unsafe
  {
     UInt16* ptr = (UInt16*) pArray.ToPointer();
      ....
  }
}