A Lesson in Multithreaded Bugs

Listing 3: interlok.hpp — C++ wrapper for interlocked variables

#ifndef INTERLOCK_HPP
#define INTERLOCK_HPP

#define STRICT
#define WIN32_LEAN_AND_MEAN
#if !defined(_INC_WINDOWS) && !defined(__WINDOWS_H)
#   include <windows.h>
#endif

class Interlock {

public:

    // Possible results of operations
    enum Results { Negative=-1, Zero=0, Positive=1 };

    // Initialise with starting value
    inline Interlock(LONG start=0);

    // Return current value
    inline operator const LONG() const;

    // Pre-increment value
    inline const Results operator ++();

    // Pre-decrement value
    inline const Results operator --();

private:

    // Can't copy Interlocks!
    Interlock(const Interlock &);

    // Can't assign Interlocks!
    Interlock &operator =(const Interlock &);

    // Current value
    LONG value;

}; // Interlock

inline Interlock::Interlock(LONG start) :
                  value(start) {
} // Interlock::Interlock(start)

inline Interlock::operator const LONG() const {
    return value;
} // Interlock::operator LONG

inline const Interlock::Results Interlock::operator ++() {
    LONG result = InterlockedIncrement(&value);
    if (result<0) return Negative;
    if (result>0) return Positive;
    return Zero;
} // Interlock::operator ++

inline const Interlock::Results Interlock::operator --() {
    LONG result = InterlockedDecrement(&value);
    if (result<0) return Negative;
    if (result>0) return Positive;
    return Zero;
} // Interlock::operator --

#endif // INTERLOCK_HPP
//End of File