/// <summary>
/// Is this Reflexive, AntiSymetic, and Transitive? Compare two VectorClocks,
/// the outcomes will be one of the following: -- Clock 1 is BEFORE clock 2
/// if there exists an i such that c1(i) <= c(2) and there does not exist a j
/// such that c1(j) > c2(j). -- Clock 1 is CONCURRANT to clock 2 if there
/// exists an i, j such that c1(i) < c2(i) and c1(j) > c2(j) -- Clock 1 is
/// AFTER clock 2 otherwise
/// </summary>
/// <param name="v1">The first VectorClock</param>
/// <param name="v2">The second VectorClock</param>
/// <returns>Whether the change occured before, after or concurrently</returns>
public static Occured Compare(VectorClock v1, VectorClock v2)
{
if (v1 == null || v2 == null)
throw new ArgumentException("Can't compare null vector clocks!");
// We do two checks: v1 <= v2 and v2 <= v1 if both are true then
bool v1Bigger = false;
bool v2Bigger = false;
int p1 = 0;
int p2 = 0;
while (p1 < v1.versions.Count && p2 < v2.versions.Count)
{
ClockEntry ver1 = v1.versions[p1];
ClockEntry ver2 = v2.versions[p2];
if (ver1.NodeId == ver2.NodeId)
{
if (ver1.Version > ver2.Version)
v1Bigger = true;
else if (ver2.Version > ver1.Version)
v2Bigger = true;
p1++;
p2++;
}
else if (ver1.NodeId > ver2.NodeId)
{
// since ver1 is bigger that means it is missing a version that ver2 has
v2Bigger = true;
p2++;
}
else
{
// this means ver2 is bigger which means it is missing a version ver1 has
v1Bigger = true;
p1++;
}
}
// Check for left overs
if (p1 < v1.versions.Count)
v1Bigger = true;
else if (p2 < v2.versions.Count)
v2Bigger = true;
// This is the case where they are equal, return BEFORE arbitrarily
if (!v1Bigger && !v2Bigger)
return Occured.Before;
// This is the case where v1 is a successor clock to v2
else if (v1Bigger && !v2Bigger)
return Occured.After;
// This is the case where v2 is a successor clock to v1
else if (!v1Bigger && v2Bigger)
return Occured.Before;
// This is the case where both clocks are parallel to one another
else
return Occured.Concurrently;
}
public VectorClock Merge(VectorClock clock)
{
VectorClock newClock = new VectorClock();
int i = 0;
int j = 0;
while (i < this.versions.Count && j < clock.versions.Count)
{
ClockEntry v1 = this.versions[i];
ClockEntry v2 = clock.versions[j];
if (v1.NodeId == v2.NodeId)
{
newClock.versions.Add(new ClockEntry(v1.NodeId,
(short)Math.Max(v1.Version,
v2.Version)));
i++;
j++;
}
else if (v1.NodeId < v2.NodeId)
{
newClock.versions.Add(v1.Clone());
i++;
}
else
{
newClock.versions.Add(v2.Clone());
j++;
}
}
// Okay now there may be leftovers on one or the other list remaining
for (int k = i; k < this.versions.Count; k++)
newClock.versions.Add(this.versions[k].Clone());
for (int k = j; k < clock.versions.Count; k++)
newClock.versions.Add(clock.versions[k].Clone());
return newClock;
}
