issue-44801 EnsureCapacity Apis For List Stack Queue

src/libraries/System.Collections/ref/System.Collections.cs

@@ -324,6 +324,7 @@ public void Clear() { }
         public void CopyTo(int index, T[] array, int arrayIndex, int count) { }
         public void CopyTo(T[] array) { }
         public void CopyTo(T[] array, int arrayIndex) { }
+        public int EnsureCapacity(int capacity) { throw null; }
         public bool Exists(System.Predicate<T> match) { throw null; }
         public T? Find(System.Predicate<T> match) { throw null; }
         public System.Collections.Generic.List<T> FindAll(System.Predicate<T> match) { throw null; }
@@ -443,6 +444,7 @@ void System.Collections.ICollection.CopyTo(System.Array array, int index) { }
         System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() { throw null; }
         public T[] ToArray() { throw null; }
         public void TrimExcess() { }
+        public int EnsureCapacity(int capacity) { throw null; }
         public bool TryDequeue([System.Diagnostics.CodeAnalysis.MaybeNullWhenAttribute(false)] out T result) { throw null; }
         public bool TryPeek([System.Diagnostics.CodeAnalysis.MaybeNullWhenAttribute(false)] out T result) { throw null; }
         public partial struct Enumerator : System.Collections.Generic.IEnumerator<T>, System.Collections.IEnumerator, System.IDisposable
@@ -699,6 +701,7 @@ public void Push(T item) { }
         System.Collections.Generic.IEnumerator<T> System.Collections.Generic.IEnumerable<T>.GetEnumerator() { throw null; }
         void System.Collections.ICollection.CopyTo(System.Array array, int arrayIndex) { }
         System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() { throw null; }
+        public int EnsureCapacity(int capacity) { throw null; }
         public T[] ToArray() { throw null; }
         public void TrimExcess() { }
         public bool TryPeek([System.Diagnostics.CodeAnalysis.MaybeNullWhenAttribute(false)] out T result) { throw null; }

src/libraries/System.Collections/src/System/Collections/Generic/Queue.cs

@@ -31,9 +31,6 @@ public class Queue<T> : IEnumerable<T>,
         private int _size;       // Number of elements.
         private int _version;
 
-        private const int MinimumGrow = 4;
-        private const int GrowFactor = 200;  // double each time
-
         // Creates a queue with room for capacity objects. The default initial
         // capacity and grow factor are used.
         public Queue()
@@ -183,12 +180,7 @@ public void Enqueue(T item)
         {
             if (_size == _array.Length)
             {
-                int newcapacity = (int)(_array.Length * (long)GrowFactor / 100);
-                if (newcapacity < _array.Length + MinimumGrow)
-                {
-                    newcapacity = _array.Length + MinimumGrow;
-                }
-                SetCapacity(newcapacity);
+                EnsureCapacityCore(_size + 1);
             }
 
             _array[_tail] = item;
@@ -385,6 +377,53 @@ public void TrimExcess()
             }
         }
 
+        /// <summary>
+        /// Ensures that the capacity of this Queue is at least the specified <paramref name="capacity"/>.
+        /// </summary>
+        /// <param name="capacity">The minimum capacity to ensure.</param>
+        public int EnsureCapacity(int capacity)
+        {
+            if (capacity < 0)
+            {
+                throw new ArgumentOutOfRangeException(nameof(capacity), capacity, SR.ArgumentOutOfRange_NeedNonNegNum);
+            }
+
+            if (_array.Length < capacity)
+            {
+                EnsureCapacityCore(capacity);
+            }
+
+            return _array.Length;
+        }
+
+        private void EnsureCapacityCore(int capacity)
+        {
+            Debug.Assert(capacity >= 0);
+
+            if (_array.Length < capacity)
+            {
+                // Array.MaxArrayLength is internal to S.P.CoreLib, replicate here.
+                const int MaxArrayLength = 0X7FEFFFFF;
+                const int GrowFactor = 2;
+                const int MinimumGrow = 4;
+
+                int newcapacity = GrowFactor * _array.Length;
+
+                // Allow the list to grow to maximum possible capacity (~2G elements) before encountering overflow.
+                // Note that this check works even when _items.Length overflowed thanks to the (uint) cast
+                if ((uint)newcapacity > MaxArrayLength) newcapacity = MaxArrayLength;
+
+                // Ensure minimum growth is respected.
+                newcapacity = Math.Max(newcapacity, _array.Length + MinimumGrow);
+
+                // If the computed capacity is still less than specified, set to the original argument.
+                // Capacities exceeding MaxArrayLength will be surfaced as OutOfMemoryException by Array.Resize.
+                if (newcapacity < capacity) newcapacity = capacity;
+
+                SetCapacity(newcapacity);
+            }
+        }
+
         // Implements an enumerator for a Queue.  The enumerator uses the
         // internal version number of the list to ensure that no modifications are
         // made to the list while an enumeration is in progress.

src/libraries/System.Collections/src/System/Collections/Generic/Stack.cs

@@ -282,12 +282,58 @@ public void Push(T item)
         [MethodImpl(MethodImplOptions.NoInlining)]
         private void PushWithResize(T item)
         {
-            Array.Resize(ref _array, (_array.Length == 0) ? DefaultCapacity : 2 * _array.Length);
+            Debug.Assert(_size == _array.Length);
+            EnsureCapacityCore(_size + 1);
             _array[_size] = item;
             _version++;
             _size++;
         }
 
+        /// <summary>
+        /// Ensures that the capacity of this Stack is at least the specified <paramref name="capacity"/>.
+        /// If the current capacity of the Stack is less than specified <paramref name="capacity"/>,
+        /// the capacity is increased by continuously twice current capacity until it is at least the specified <paramref name="capacity"/>.
+        /// </summary>
+        /// <param name="capacity">The minimum capacity to ensure.</param>
+        public int EnsureCapacity(int capacity)
+        {
+            if (capacity < 0)
+            {
+                throw new ArgumentOutOfRangeException(nameof(capacity), capacity, SR.ArgumentOutOfRange_NeedNonNegNum);
+            }
+
+            if (_array.Length < capacity)
+            {
+                EnsureCapacityCore(capacity);
+                _version++;
+            }
+
+            return _array.Length;
+        }
+
+        private void EnsureCapacityCore(int capacity)
+        {
+            Debug.Assert(capacity >= 0);
+
+            if (_array.Length < capacity)
+            {
+                // Array.MaxArrayLength is internal to S.P.CoreLib, replicate here.
+                const int MaxArrayLength = 0X7FEFFFFF;
+
+                int newcapacity = _array.Length == 0 ? DefaultCapacity : 2 * _array.Length;
+
+                // Allow the list to grow to maximum possible capacity (~2G elements) before encountering overflow.
+                // Note that this check works even when _items.Length overflowed thanks to the (uint) cast.
+                if ((uint)newcapacity > MaxArrayLength) newcapacity = MaxArrayLength;
+
+                // If computed capacity is still less than specified, set to the original argument.
+                // Capacities exceeding MaxArrayLength will be surfaced as OutOfMemoryException by Array.Resize.
+                if (newcapacity < capacity) newcapacity = capacity;
+
+                Array.Resize(ref _array, newcapacity);
+            }
+        }
+
         // Copies the Stack to an array, in the same order Pop would return the items.
         public T[] ToArray()
         {

src/libraries/System.Collections/tests/Generic/List/List.Generic.Tests.EnsureCapacity.cs

@@ -0,0 +1,108 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Collections.Generic;
+using Xunit;
+
+namespace System.Collections.Tests
+{
+    /// <summary>
+    /// Contains tests that ensure the correctness of the List class.
+    /// </summary>
+    public abstract partial class List_Generic_Tests<T> : IList_Generic_Tests<T>
+    {
+        [Theory]
+        [MemberData(nameof(ValidCollectionSizes))]
+        public void EnsureCapacity_RequestingLargerCapacity_DoesInvalidateEnumeration(int count)
+        {
+            List<T> list = GenericListFactory(count);
+            IEnumerator<T> copiedListEnumerator = new List<T>(list).GetEnumerator();
+            IEnumerator<T> enumerator = list.GetEnumerator();
+            var capacity = list.Capacity;
+
+            list.EnsureCapacity(capacity + 1);
+
+            Assert.Throws<InvalidOperationException>(() => enumerator.MoveNext());
+        }
+
+        [Fact]
+        public void EnsureCapacity_NotInitialized_RequestedZero_ReturnsZero()
+        {
+            var list = new List<T>();
+            Assert.Equal(0, list.EnsureCapacity(0));
+            Assert.Equal(0, list.Capacity);
+        }
+
+        [Fact]
+        public void EnsureCapacity_NegativeCapacityRequested_Throws()
+        {
+            var list = new List<T>();
+            AssertExtensions.Throws<ArgumentOutOfRangeException>("capacity", () => list.EnsureCapacity(-1));
+        }
+
+        const int MaxArraySize = 0X7FEFFFFF;
+
+        [Theory]
+        [InlineData(5, MaxArraySize + 1)]
+        [InlineData(1, int.MaxValue)]
+        [SkipOnMono("mono forces no restrictions on array size.")]
+        public void EnsureCapacity_LargeCapacity_Throws(int count, int requestCapacity)
+        {
+            List<T> list = GenericListFactory(count);
+            Assert.Throws<OutOfMemoryException>(() => list.EnsureCapacity(requestCapacity));
+        }
+
+        [Theory]
+        [InlineData(5)]
+        public void EnsureCapacity_RequestedCapacitySmallerThanOrEqualToCurrent_CapacityUnchanged(int currentCapacity)
+        {
+            var list = new List<T>(currentCapacity);
+
+            for (int requestCapacity = 0; requestCapacity <= currentCapacity; requestCapacity++)
+            {
+                Assert.Equal(currentCapacity, list.EnsureCapacity(requestCapacity));
+                Assert.Equal(currentCapacity, list.Capacity);
+            }
+        }
+
+        [Theory]
+        [MemberData(nameof(ValidCollectionSizes))]
+        public void EnsureCapacity_RequestedCapacitySmallerThanOrEqualToCount_CapacityUnchanged(int count)
+        {
+            List<T> list = GenericListFactory(count);
+            var currentCapacity = list.Capacity;
+
+            for (int requestCapacity = 0; requestCapacity <= count; requestCapacity++)
+            {
+                Assert.Equal(currentCapacity, list.EnsureCapacity(requestCapacity));
+                Assert.Equal(currentCapacity, list.Capacity);
+            }
+        }
+
+        [Theory]
+        [InlineData(0)]
+        [InlineData(1)]
+        [InlineData(5)]
+        public void EnsureCapacity_CapacityIsAtLeastTheRequested(int count)
+        {
+            List<T> list = GenericListFactory(count);
+
+            int currentCapacity = list.Capacity;
+            int requestCapacity = currentCapacity + 1;
+            int newCapacity = list.EnsureCapacity(requestCapacity);
+            Assert.InRange(newCapacity, requestCapacity, int.MaxValue);
+        }
+
+        [Theory]
+        [MemberData(nameof(ValidCollectionSizes))]
+        public void EnsureCapacity_RequestingLargerCapacity_DoesNotImpactListContent(int count)
+        {
+            List<T> list = GenericListFactory(count);
+            var copiedList = new List<T>(list);
+
+            list.EnsureCapacity(list.Capacity + 1);
+            Assert.Equal(copiedList, list);
+        }
+    }
+}

src/libraries/System.Collections/tests/Generic/Queue/Queue.Generic.Tests.cs

@@ -320,5 +320,97 @@ public void Queue_Generic_TryPeek_EmptyQueue_ReturnsFalse()
             Assert.False(new Queue<T>().TryPeek(out result));
             Assert.Equal(default(T), result);
         }
+
+        [Theory]
+        [MemberData(nameof(ValidCollectionSizes))]
+        public void Queue_Generic_EnsureCapacity_RequestingLargerCapacity_DoesInvalidateEnumeration(int count)
+        {
+            Queue<T> queue = GenericQueueFactory(count);
+            IEnumerator<T> copiedEnumerator = new List<T>(queue).GetEnumerator();
+            IEnumerator<T> enumerator = queue.GetEnumerator();
+
+            queue.EnsureCapacity(count + 1);
+
+            Assert.Throws<InvalidOperationException>(() => enumerator.MoveNext());
+        }
+
+        [Fact]
+        public void Queue_Generic_EnsureCapacity_NotInitialized_RequestedZero_ReturnsZero()
+        {
+            var queue = GenericQueueFactory();
+            Assert.Equal(0, queue.EnsureCapacity(0));
+        }
+
+        [Fact]
+        public void Queue_Generic_EnsureCapacity_NegativeCapacityRequested_Throws()
+        {
+            var queue = GenericQueueFactory();
+            AssertExtensions.Throws<ArgumentOutOfRangeException>("capacity", () => queue.EnsureCapacity(-1));
+        }
+
+        const int MaxArraySize = 0X7FEFFFFF;
+
+        [Theory]
+        [InlineData(MaxArraySize + 1)]
+        [InlineData(int.MaxValue)]
+        [SkipOnMono("mono forces no restrictions on array size.")]
+        public void Queue_Generic_EnsureCapacity_LargeCapacityRequested_Throws(int requestedCapacity)
+        {
+            var queue = GenericQueueFactory();
+            AssertExtensions.Throws<OutOfMemoryException>(() => queue.EnsureCapacity(requestedCapacity));
+        }
+
+        [Theory]
+        [InlineData(5)]
+        public void Queue_Generic_EnsureCapacity_RequestedCapacitySmallerThanOrEqualToCurrent_CapacityUnchanged(int currentCapacity)
+        {
+            var queue = new Queue<T>(currentCapacity);
+
+            for (int requestCapacity = 0; requestCapacity <= currentCapacity; requestCapacity++)
+            {
+                Assert.Equal(currentCapacity, queue.EnsureCapacity(requestCapacity));
+            }
+        }
+
+        [Theory]
+        [MemberData(nameof(ValidCollectionSizes))]
+        public void Queue_Generic_EnsureCapacity_RequestedCapacitySmallerThanOrEqualToCount_CapacityUnchanged(int count)
+        {
+            Queue<T> queue = GenericQueueFactory(count);
+
+            for (int requestCapacity = 0; requestCapacity <= count; requestCapacity++)
+            {
+                Assert.Equal(count, queue.EnsureCapacity(requestCapacity));
+            }
+        }
+
+        [Theory]
+        [InlineData(0)]
+        [InlineData(1)]
+        [InlineData(5)]
+        public void Queue_Generic_EnsureCapacity_CapacityIsAtLeastTheRequested(int count)
+        {
+            Queue<T> queue = GenericQueueFactory(count);
+
+            int requestCapacity = count + 1;
+            int newCapacity = queue.EnsureCapacity(requestCapacity);
+            Assert.InRange(newCapacity, requestCapacity, int.MaxValue);
+        }
+
+        [Theory]
+        [MemberData(nameof(ValidCollectionSizes))]
+        public void Queue_Generic_EnsureCapacity_RequestingLargerCapacity_DoesNotImpactQueueContent(int count)
+        {
+            Queue<T> queue = GenericQueueFactory(count);
+            var copiedList = new List<T>(queue);
+
+            queue.EnsureCapacity(count + 1);
+            Assert.Equal(copiedList, queue);
+
+            for (int i = 0; i < count; i++)
+            {
+                Assert.Equal(copiedList[i], queue.Dequeue());
+            }
+        }
     }
 }