[Bleeding] Change Vec3DPool to a stack based pool

Avoid overhead of using an ArrayList and resizing it. Also allows for reuse
of objects in the pool during the same tick by explicitly releasing them
back to the pool. This allows for much better cache performance as well
as reduced cache footprint.

src/main/java/net/minecraft/server/Vec3D.java

@@ -6,6 +6,7 @@ public class Vec3D {
     public double a;
     public double b;
     public double c;
+    public Vec3D next; // CraftBukkit
 
     public static Vec3D a(double d0, double d1, double d2) {
         return new Vec3D(d0, d1, d2);

src/main/java/net/minecraft/server/Vec3DPool.java

@@ -7,7 +7,16 @@ public class Vec3DPool {
 
     private final int a;
     private final int b;
-    private final List c = new ArrayList();
+    // CraftBukkit start
+    // private final List c = new ArrayList();
+    private Vec3D freelist = null;
+    private Vec3D alloclist = null;
+    private Vec3D freelisthead = null;
+    private Vec3D alloclisthead = null;
+    private int total_size = 0;
+    private int hit;
+    private int miss;
+    // CraftBukkit end
     private int d = 0;
     private int e = 0;
     private int f = 0;
@@ -17,36 +26,72 @@ public class Vec3DPool {
         this.b = j;
     }
 
-    public Vec3D create(double d0, double d1, double d2) {
+    public final Vec3D create(double d0, double d1, double d2) { // CraftBukkit - add final
         if (this.f == 0) return new Vec3D(d0, d1, d2); // CraftBukkit - don't pool objects indefinitely if thread doesn't adhere to contract
         Vec3D vec3d;
 
-        if (this.d >= this.c.size()) {
+        if (this.freelist == null) { // CraftBukkit
             vec3d = new Vec3D(d0, d1, d2);
-            this.c.add(vec3d);
+            this.total_size++; // CraftBukkit
         } else {
-            vec3d = (Vec3D) this.c.get(this.d);
+            // CraftBukkit start
+            vec3d = this.freelist;
+            this.freelist = vec3d.next;
+            // CraftBukkit end
             vec3d.b(d0, d1, d2);
         }
 
+        // CraftBukkit start
+        if (this.alloclist == null) {
+            this.alloclisthead = vec3d;
+        }
+        vec3d.next = this.alloclist; // add to allocated list
+        this.alloclist = vec3d;
+        // CraftBukkit end
         ++this.d;
         return vec3d;
     }
     
+    // CraftBukkit start - offer back vector (can save LOTS of unneeded bloat) - works about 90% of the time
+    public void release(Vec3D v) {
+        if (this.alloclist == v) {
+            this.alloclist = v.next; // Pop off alloc list
+            // Push on to free list
+            if (this.freelist == null) this.freelisthead = v;
+            v.next = this.freelist;
+            this.freelist = v;
+            this.d--;
+        }
+    }
+    // CraftBukkit end
+
     public void a() {
         if (this.d > this.e) {
             this.e = this.d;
         }
 
         // CraftBukkit start - intelligent cache
+        // Take any allocated blocks and put them on free list
+        if (this.alloclist != null) {
+            if (this.freelist == null) {
+                this.freelist = this.alloclist;
+                this.freelisthead = this.alloclisthead;
+            }
+            else {
+                this.alloclisthead.next = this.freelist;
+                this.freelist = this.alloclist;
+                this.freelisthead = this.alloclisthead;
+            }
+            this.alloclist = null;
+        }
         if ((this.f++ & 0xff) == 0) {
-            int newSize = this.c.size() - (this.c.size() >> 3);
+            int newSize = total_size - (total_size >> 3);
             if (newSize > this.e) { // newSize will be 87.5%, but if we were not in that range, we clear some of the cache
-                for (int i = this.c.size() - 1; i > newSize; i--) { // Work down from size() to prevent insane array copies
-                    this.c.remove(i);
+                for (int i = total_size; i > newSize; i--) {
+                    freelist = freelist.next;
                 }
+                total_size = newSize;
             }
-
             this.e = 0;
             // this.f = 0; // We do not reset to zero; it doubles for a flag
         }

src/main/java/net/minecraft/server/World.java

@@ -742,9 +742,11 @@ public abstract class World implements IBlockAccess {
                         MovingObjectPosition movingobjectposition1 = block1.a(this, l, i1, j1, vec3d, vec3d1);
 
                         if (movingobjectposition1 != null) {
+                            Vec3D.a().release(vec3d2); // CraftBukkit
                             return movingobjectposition1;
                         }
                     }
+                    Vec3D.a().release(vec3d2); // CraftBukkit
                 }
 
                 return null;
@@ -1446,6 +1448,7 @@ public abstract class World implements IBlockAccess {
                 entity.motY += vec3d.b * d1;
                 entity.motZ += vec3d.c * d1;
             }
+            Vec3D.a().release(vec3d); // CraftBukkit - pop it - we're done
 
             return flag;
         }
@@ -1526,6 +1529,7 @@ public abstract class World implements IBlockAccess {
         int i = 0;
         int j = 0;
 
+        Vec3D vec3d2 = Vec3D.a().create(0, 0, 0); // CraftBukkit
         for (float f = 0.0F; f <= 1.0F; f = (float) ((double) f + d0)) {
             for (float f1 = 0.0F; f1 <= 1.0F; f1 = (float) ((double) f1 + d1)) {
                 for (float f2 = 0.0F; f2 <= 1.0F; f2 = (float) ((double) f2 + d2)) {
@@ -1533,7 +1537,7 @@ public abstract class World implements IBlockAccess {
                     double d4 = axisalignedbb.b + (axisalignedbb.e - axisalignedbb.b) * (double) f1;
                     double d5 = axisalignedbb.c + (axisalignedbb.f - axisalignedbb.c) * (double) f2;
 
-                    if (this.a(Vec3D.a().create(d3, d4, d5), vec3d) == null) {
+                    if (this.a(vec3d2.b(d3, d4, d5), vec3d) == null) { // CraftBukkit
                         ++i;
                     }
 
@@ -1541,6 +1545,7 @@ public abstract class World implements IBlockAccess {
                 }
             }
         }
+        Vec3D.a().release(vec3d2); // CraftBukkit
 
         return (float) i / (float) j;
     }