ring buffer

Author: beston123

src/main/java/code/algorithm/search/BinarySearch.java

@@ -1,12 +1,10 @@
 package code.algorithm.search;
 
-import org.apache.commons.lang3.tuple.Pair;
-
 import java.util.Arrays;
 
 /**
  * 〈二分查找〉<p>
- * 〈功能详细描述〉
+ * 最坏时间复杂度：O(log n)
  *
  * @author zixiao
  * @date 2019/11/27

src/main/java/code/collection/ringbuffer/RingBuffer.java

@@ -0,0 +1,54 @@
+package code.collection.ringbuffer;
+
+/**
+ * 〈环形缓冲区〉<p>
+ * 〈功能详细描述〉
+ *
+ * @author zixiao
+ * @date 2019/12/23
+ */
+public class RingBuffer<E> {
+
+    private int bufferSize;
+
+    private Object[] entries;
+
+    private final int indexMask;
+
+    private final Sequencer sequencer;
+
+    public RingBuffer(int bufferSize) {
+        if (Integer.bitCount(bufferSize) != 1) {
+            this.bufferSize = get2Power(bufferSize);
+        } else {
+            this.bufferSize = bufferSize;
+        }
+        this.indexMask = bufferSize - 1;
+        this.entries = new Object[this.bufferSize];
+        this.sequencer = new Sequencer(this.bufferSize);
+    }
+
+    private int get2Power(int capacity) {
+        int n = capacity - 1;
+        n |= n >>> 1;
+        n |= n >>> 2;
+        n |= n >>> 4;
+        n |= n >>> 8;
+        n |= n >>> 16;
+        return n + 1;
+    }
+
+    public E get(long seq){
+        Long idx = seq & indexMask;
+        return (E)entries[idx.intValue()];
+    }
+
+    public long next() {
+        return sequencer.next();
+    }
+
+    public long next(int n) {
+        return sequencer.next(n);
+    }
+
+}

src/main/java/code/collection/ringbuffer/Sequencer.java

@@ -0,0 +1,50 @@
+package code.collection.ringbuffer;
+
+import java.util.concurrent.atomic.AtomicLong;
+
+/**
+ * 〈一句话功能简述〉<p>
+ * 〈功能详细描述〉
+ *
+ * @author zixiao
+ * @date 2019/12/23
+ */
+public class Sequencer {
+
+    protected final int bufferSize;
+
+    // 使用sequence代替，实现缓存行填充来消除伪共享
+    private final AtomicLong cursor = new AtomicLong(-1);
+
+    private final int[] availableBuffer;
+
+    private final int indexMask;
+
+    public Sequencer(int bufferSize) {
+        this.bufferSize = bufferSize;
+        if(Integer.bitCount(bufferSize) != 1){
+            throw new IllegalArgumentException("bufferSize must be a power of 2");
+        }
+        availableBuffer = new int[this.bufferSize];
+        indexMask = this.bufferSize - 1;
+    }
+
+    public long next(){
+        return next(1);
+    }
+
+    public long next(int n) {
+        long current = cursor.get();
+        long next;
+        do {
+            next = current + n;
+            // CAS申请n个位置
+            if (cursor.compareAndSet(current, next)) {
+                break;
+            }
+        } while (true);
+        return next;
+    }
+
+
+}