/// <summary>
/// Merge clocks
/// </summary>
public VectorClock Merge(VectorClock clock)
{
int i = 0;
int j = 0;
var versions = Versions.ToArray();
var clockVersions = clock.Versions.ToArray();
var newClockVersions = List.empty <ClockEntry>();
while (i < versions.Length && j < clockVersions.Length)
{
var v1 = versions[i];
var v2 = clockVersions[j];
if (v1.NodeId == v2.NodeId)
{
var nc = new ClockEntry(v1.NodeId, (int)Math.Max(v1.Version, v2.Version));
newClockVersions = newClockVersions.Add(nc);
i++;
j++;
}
else if (v1.NodeId < v2.NodeId)
{
newClockVersions = newClockVersions.Add(v1);
i++;
}
else
{
newClockVersions = newClockVersions.Add(v2);
j++;
}
}
// Okay now there may be leftovers on one or the other list remaining
for (int k = i; k < versions.Length; k++)
{
newClockVersions = newClockVersions.Add(versions[k]);
}
for (int k = j; k < clockVersions.Length; k++)
{
newClockVersions = newClockVersions.Add(clockVersions[k]);
}
return(new VectorClock(newClockVersions));
}
/// <summary>
/// <para>
/// Is this reflexive, antisymetic, and transitive? Compare two VectorClocks,
/// the outcomes will be one of the following:
/// </para>
/// <para>
/// * 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).
/// </para>
/// <para>
/// * Clock 1 is /concurrent/ to clock 2 if there exists an i, j such that
/// c1(i) < c2(i) and c1(j) > c2(j)
/// </para>
/// <para>
/// * Clock 1 is /after/ clock 2 otherwise
/// </para>
/// </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);
}
}
