add some tools

src/Shared/HandyControl_Shared/Tools/Pool/IPool!1.cs

@@ -0,0 +1,9 @@
+namespace HandyControl.Tools
+{
+    public interface IPool<T>
+    {
+        T Acquire();
+
+        bool Release(T instance);
+    }
+}

src/Shared/HandyControl_Shared/Tools/Pool/SimplePool!1.cs

@@ -0,0 +1,64 @@
+//adapted from https://android.googlesource.com/platform/frameworks/base/+/master/core/java/android/util/Pools.java
+
+using System;
+
+namespace HandyControl.Tools
+{
+    public class SimplePool<T> : IPool<T>
+    {
+        private readonly object[] _pool;
+
+        private int _poolSize;
+
+        public SimplePool(int maxPoolSize)
+        {
+            if (maxPoolSize <= 0)
+            {
+                throw new ArgumentException("The max pool size must be > 0");
+            }
+            _pool = new object[maxPoolSize];
+        }
+
+        public virtual T Acquire()
+        {
+            if (_poolSize > 0)
+            {
+                var lastPooledIndex = _poolSize - 1;
+                var instance = (T)_pool[lastPooledIndex];
+                _pool[lastPooledIndex] = null;
+                _poolSize--;
+                return instance;
+            }
+            return default;
+        }
+
+        public virtual bool Release(T instance)
+        {
+            if (IsInPool(instance))
+            {
+                throw new Exception("Already in the pool!");
+            }
+
+            if (_poolSize < _pool.Length)
+            {
+                _pool[_poolSize] = instance;
+                _poolSize++;
+                return true;
+            }
+
+            return false;
+        }
+
+        private bool IsInPool(T instance)
+        {
+            for (var i = 0; i < _poolSize; i++)
+            {
+                if (Equals(_pool[i], instance))
+                {
+                    return true;
+                }
+            }
+            return false;
+        }
+    }
+}

src/Shared/HandyControl_Shared/Tools/Pool/SynchronizedPool!1.cs

@@ -0,0 +1,27 @@
+namespace HandyControl.Tools
+{
+    public class SynchronizedPool<T> : SimplePool<T>
+    {
+        private readonly object _lockObj = new object();
+
+        public SynchronizedPool(int maxPoolSize) : base(maxPoolSize)
+        {
+            
+        }
+
+        public override T Acquire()
+        {
+            lock (_lockObj)
+            {
+                return base.Acquire();
+            }
+        }
+
+        public override bool Release(T element)
+        {
+            lock (_lockObj) {
+                return base.Release(element);
+            }
+        }
+    }
+}