/// <summary>
/// Collects the elements in quadrant that pass the intersection test.
/// </summary>
/// <param name="lockedQuadrant">A quadrant on which the current thread
/// holds a shared lock.</param>
/// <param name="intersectionTest">An predicate P such that if a
/// rectangle B contains a rectangle A, then P(A) implies P(B).</param>
/// <param name="output">The output collection where to place the elements.</param>
void CollectElementsInQuadrantThatAreInRegion(Quadrant lockedQuadrant,
Predicate <Rect> intersectionTest, ICollection <IElement> output)
{
Debug.Assert(lockedQuadrant.Lock.ThreadOwnsSharedLock);
if (lockedQuadrant.IsLeaf)
{
foreach (var datum in lockedQuadrant.Data)
{
Rect datumRect = new Rect(datum.Coordinates.Longitude, datum.Coordinates.Latitude, 0, 0);
if (intersectionTest(datumRect))
{
output.Add(datum);
}
}
lockedQuadrant.Lock.ExitSharedLock();
}
else
{
// Lock all children. Do this before releasing the lock
// on the parent to prevent the parent from performing a join.
for (int childIdx = 0; childIdx < 4; ++childIdx)
{
lockedQuadrant.GetChild(childIdx).Lock.EnterSharedLock();
}
// Exit the lock on the parent before recursion to avoid
// holding a shared lock on every quadrant all the way down.
lockedQuadrant.Lock.ExitSharedLock();
// Check each child.
for (int childIdx = 0; childIdx < 4; ++childIdx)
{
Quadrant child = lockedQuadrant.GetChild(childIdx);
if (intersectionTest(child.Bounds))
{
CollectElementsInQuadrantThatAreInRegion(child, intersectionTest, output);
}
else
{
child.Lock.ExitSharedLock();
}
}
}
}
void SubdivideWithoutLocking(Quadrant quadrant)
{
if (quadrant.SubdivisionLevel >= maxSubdivisionLevel)
{
return;
}
if (quadrant.Data.Count <= maxLeafCapacity)
{
return;
}
if (!quadrant.TrySubdivide())
{
return;
}
for (int childIdx = 0; childIdx < 4; ++childIdx)
{
Quadrant child = quadrant.GetChild(childIdx);
foreach (var datum in child.Data)
{
elementsToNodes[datum] = child;
}
if (child.Data.Count > maxLeafCapacity)
{
SubdivideWithoutLocking(child);
}
}
}
/// <summary>
/// Gets the depth of the tree rooted at this quadrant. For efficiency,
/// this performs no locking. Because of this, the return value should be
/// regarded as an approximation.
/// </summary>
int GetApproximateLargestSubdivisionLevel(Quadrant quadrant)
{
if (quadrant.IsLeaf)
{
return(0);
}
int maxLevel = 1;
for (int childIdx = 0; childIdx < 4; ++childIdx)
{
try
{
int childLevel = 1 + GetApproximateLargestSubdivisionLevel(quadrant.GetChild(childIdx));
if (childLevel > maxLevel)
{
maxLevel = childLevel;
}
}
catch (ApplicationException)
{
// This can happen if the quadrant becomes a leaf due to
// a join operation (since we didn't lock it).
break;
}
}
return(maxLevel);
}
