[LinkedIn] Implement a thread safe hashtable-优快云博客

本文介绍了一个使用LinkedList实现的线程安全HashMap，通过在每个实例级别获取锁来确保多个线程不能同时访问同一实例上的put/get操作。

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/*
 * before entering into synchronized method or block thread needs to acquire the lock
 * Here different thread cannot access "put" / "get" from the same instance of hashmap at the same time
 * The lock is obtained at the object level, meaning if t1 is using put(), t2 cannot use get() simultaneously
 */

public ThreadSafeHashMap() {
   items = (LinkedList<Cell<K, V>>[]) new LinkedList[cap];
 }

 public int hashCode(K key) {
   return key.toString().length() % items.length;
 }

 public synchronized void put(K key, V value) {
   int x = hashCode(key);
   if (items[x] == null) {
     items[x] = new LinkedList<Cell<K, V>>();
   }
   LinkedList<Cell<K, V>> list = items[x];
   for (Cell<K, V> c : list) {
     if (c.equals(key)) {
       list.remove(c);
       break;
     }
   }
   Cell<K, V> cell = new Cell<K, V>(key, value);
   list.add(cell);
 }


public synchronized V get(K key) {
   int x = hashCode(key);
   if (items[x] == null) {
     return null;
   }
   LinkedList<Cell<K, V>> list = items[x];
   for (Cell<K, V> c : list) {
     if (c.equals(key)) {
       return c.getValue();
     }
   }
   return null;
 }
}