add design

design/blocking_queue.java

@@ -0,0 +1,28 @@
+public class BlockingQueueImpl<T> implements BlockingQueue<T>
+{
+  private final Queue<T> q = new LinkedList<T>();
+  private final int maxSize;
+  private final Object mutex = new Object();
+
+  public BlockingQueueImpl(int maxSize) {
+    if (maxSize <= 0)
+      throw new IllegalArgumentException("maxSize=" + maxSize);
+    this.maxSize = maxSize;
+  }
+
+  public T take() throws InterruptedException {
+    synchronized (mutex) {
+      while (q.isEmpty()) mutex.wait();
+      mutex.notifyAll(); // Wake up threads waiting to put (or take)
+      return q.remove();
+    }
+  }
+
+  public void put(T obj) throws InterruptedException {
+    synchronized (mutex) {
+      while (q.size() >= maxSize) mutex.wait();
+      mutex.notifyAll(); // Wake up threads waiting to take (or put)
+      q.add(obj);
+    }
+  }
+}

design/requests.c

@@ -0,0 +1,47 @@
+#include <time.h>
+#include <sys/time.h>
+long now() {
+    struct timeval time;
+    gettimeofday(&time, NULL);
+    return (time.tv_sec * 1000000 + time.tv_usec);
+}
+
+class HitCounter {
+private:
+    deque<pair<long, int>> hits;
+    long last_count = 0;
+    const int second = 1000000;
+    const int minute = 60 * second;
+    const int hour = 60 * minute;
+
+    void prune() {
+        auto old = upper_bound(hits.begin(), hits.end(), make_pair(now() - 1 * hour, -1));
+        if (old != hits.end()) {
+            hits.erase(hits.begin(), old);
+        }
+    }
+
+public:
+    void hit() {
+        hits.push_back(make_pair(now(), ++last_count));
+        prune();
+    }
+
+    long hitsInLastSecond() {
+        auto before = lower_bound(hits.begin(), hits.end(), make_pair(now() - 1 * second, -1));
+        if (before == hits.end()) { return 0; }
+        return last_count - before->second + 1;
+    }
+
+    long hitsInLastMinute() {
+        auto before = lower_bound(hits.begin(), hits.end(), make_pair(now() - 1 * minute, -1));
+        if (before == hits.end()) { return 0; }
+        return last_count - before->second + 1;
+    }
+
+    long hitsInLastHour() {
+        auto before = lower_bound(hits.begin(), hits.end(), make_pair(now() - 1 * hour, -1));
+        if (before == hits.end()) { return 0; }
+        return last_count - before->second + 1;
+    }
+};

design/singleton.c

@@ -0,0 +1,29 @@
+// Example for singleton pattern
+// class definition
+class MySingleton {
+private:
+// Private Constructor
+    MySingleton();
+// Stop the compiler generating methods of copy the object
+    MySingleton(const MySingleton &copy);    // Not Implemented
+    MySingleton &operator=(const MySingleton &copy);    // Not Implemented
+    static MySingleton *m_pInstance;
+public:
+    static MySingleton *getSharedInstance() {
+        if (!m_pInstance) {
+            m_pInstance = new MySingleton;
+        }
+        return m_pInstance;
+    }
+};
+
+// in the source file
+MySingleton *MySingleton::m_pInstance = NULL;
+
+注意，本例中的实现方式针对非多线程的情况。如果有过个线程想要同时调用getSharedInstance函数，则需要用mutex保护下列代码：
+        pthread_mutex_lock(&mutex);
+        if (!m_pInstance) {
+            m_pInstance = new MySingleton;
+        }
+        pthread_mutex_unlock(&mutex);
+