程序清单 12-1 基于信号量的有界缓存

Author: zhangquanli

src/main/java/chapter_12/code_01/SemaphoreBoundedBuffer.java

@@ -0,0 +1,62 @@
+package chapter_12.code_01;
+
+import net.jcip.annotations.GuardedBy;
+import net.jcip.annotations.ThreadSafe;
+
+import java.util.concurrent.Semaphore;
+
+/**
+ * 程序清单 12-1 基于信号量的有界缓存
+ */
+@ThreadSafe
+public class SemaphoreBoundedBuffer<E> {
+    private final Semaphore availableItems, availableSpaces;
+    @GuardedBy("this")
+    private final E[] items;
+    @GuardedBy("this")
+    private int putPosition = 0, takePosition = 0;
+
+    public SemaphoreBoundedBuffer(int capacity) {
+        if (capacity <= 0) {
+            throw new IllegalArgumentException();
+        }
+        availableItems = new Semaphore(0);
+        availableSpaces = new Semaphore(capacity);
+        items = (E[]) new Object[capacity];
+    }
+
+    public boolean isEmpty() {
+        return availableItems.availablePermits() == 0;
+    }
+
+    public boolean isFull() {
+        return availableSpaces.availablePermits() == 0;
+    }
+
+    public void put(E x) throws InterruptedException {
+        availableSpaces.acquire();
+        doInert(x);
+        availableItems.release();
+    }
+
+    public E take() throws InterruptedException {
+        availableItems.acquire();
+        E item = doExtract();
+        availableSpaces.release();
+        return item;
+    }
+
+    private synchronized void doInert(E x) {
+        int i = putPosition;
+        items[i] = x;
+        putPosition = (++i == items.length) ? 0 : i;
+    }
+
+    private synchronized E doExtract() {
+        int i = takePosition;
+        E x = items[i];
+        items[i] = null;
+        takePosition = (++i == items.length) ? 0 : i;
+        return x;
+    }
+}