Win32 Read/Write Lock Using Only Critical Sections

Question

I have to implement a read/write lock in C++ using the Win32 api as part of a project at work. All of the existing solutions use kernel objects (semaphores and mutexes) tha

Answer 1

Look my implementation here:

https://github.com/coolsoftware/LockLib

VRWLock is a C++ class that implements single writer - multiple readers logic.

Look also test project TestLock.sln.

UPD. Below is the simple code for reader and writer:

LONG gCounter = 0;

// reader

for (;;) //loop
{
  LONG n = InterlockedIncrement(&gCounter); 
  // n = value of gCounter after increment
  if (n <= MAX_READERS) break; // writer does not write anything - we can read
  InterlockedDecrement(&gCounter);
}
// read data here
InterlockedDecrement(&gCounter); // release reader

// writer

for (;;) //loop
{
  LONG n = InterlockedCompareExchange(&gCounter, (MAX_READERS+1), 0); 
  // n = value of gCounter before attempt to replace it by MAX_READERS+1 in InterlockedCompareExchange
  // if gCounter was 0 - no readers/writers and in gCounter will be MAX_READERS+1
  // if gCounter was not 0 - gCounter stays unchanged
  if (n == 0) break;
}
// write data here
InterlockedExchangeAdd(&gCounter, -(MAX_READERS+1)); // release writer

VRWLock class supports spin count and thread-specific reference count that allows to release locks of terminated threads.