CircularBuffer<T> Class

The CircularBuffer<T> class is a data structure that uses a single, fixed-size buffer that behaves as if it were connected end-to-end. You can use it as collection of objects with automatic overwrite support and no array resizing or allocations. The design of the buffer allows it to be used as both a first-in, first-out queue, or a first-in, last-out stack.

You can drop the class directly into your projects to use as-is, or reference the assembly. A NuGet package is also available. The class has no external dependencies aside from a reference to System.dll.

View the change log for updates to this library.

Overwrite support

By default, the contents of the buffer automatically wrap, so for example if you create a buffer with a maximum capacity of 10, but then attempt to add 11 items, the oldest item in the buffer will be automatically overwritten.

Alternatively, you can set the AllowOverwrite property to false, in which case attempting to add that eleventh item would throw an exception.

Performance

The internal buffer of the class is created whenever the Capacity property is set. Generally, this means it will be created once for the lifetime of the class, unless for some reason you want to dynamically manipulate the capacity. Internally, CircularBuffer<T> has Head and Tail properties which represent the start and end of the buffer, so as you Put and Get items, these values will be adjusted accordingly. No resizing of buffers or reallocation.

Note: Calling the Clear method currently also reallocates the internal buffer rather than looping all the items and setting them to default(T).

The PeekLast(count), GetLast(count), Get(count) and ToArray methods will all create and return a new array. With the exception of ToArray (as there is already CopyTo), the other methods have overloads that allow you to specify an existing array to be populated.

Using the class

The CircularBuffer<T> mostly acts as a FIFO queue. You can use the Put method to put one or more items into the buffer, and then retrieve one or more items using one of the Get methods. However, you can also use it as FILO stack by using the GetLast method.

Note: When you retrieve an item (or items), references to the items still remain in the internal buffer. The Head and Size properties are adjusted so that you'll never get that item again no matter what methods you call. I'm not sure yet whether that is an acceptable approach, or if I should reset the entry to default(T).

To retrieve the next item without removing it from the buffer, you can use the Peek method. Or, to retrieve (again without removing) the last item in the buffer, you can use PeekLast. To round off peeking, there is also a PeekAt method which can retrieve an item from anywhere in the buffer.

Calling Get, GetLast, Peek or PeekLast on an empty buffer will thrown an exception. You can use IsEmpty to check if these actions will succeed. Similarly, calling Put on a full buffer with overwriting disabled will also throw an exception. You can use IsFull to check if this is the case.

The Size property allows you to see how many items you've added to the buffer. The Capacity property returns the maximum number of items the buffer can hold before the oldest items will be overwritten.

The ToArray method will return all queued items, or you can use CopyTo as a more advanced alternative.

The CircularBuffer<T> class implements IEnumerable<T> and IEnumerable, so you can happily iterate over the items - this won't remove them from the buffer. It also implements ICollection<T> and ICollection although calling ICollection<T>.Remove is not supported and will throw an exception.

Finally, the Clear method will reset the buffer to an empty state.

Although I don't think they'll be needed much in real-world use, the Head property represents the internal index of the next item to be read from the buffer. The Tail property represents the index of the next item to be written.

Examples

This first example creates a CircularBuffer<T>, adds four items, then retrieves the first item. The comments describe how the internal state of the buffer changes with each call.

  CircularBuffer<string> target;
  string firstItem;
  string[] items;

  target = new CircularBuffer<string>(10); // Creates a buffer for storing up to 10 items
  target.Put("Alpha");                     // Head is 0, Tail is 1, Size is 1
  target.Put("Beta");                      // Head is 0, Tail is 2, Size is 2
  target.Put("Gamma");                     // Head is 0, Tail is 3, Size is 3
  target.Put("Delta");                     // Head is 0, Tail is 4, Size is 4

  firstItem = target.Get();                // firstItem is Alpha. Head is 1, Tail is 4, Size is 3
  items = target.ToArray();                // items are Beta, Gamma, Delta. Head, Tail and Size are unchanged.

This second example shows how the buffer will automatically overwrite the oldest items when full.

  CircularBuffer<string> target;
  string firstItem;
  string[] items;

  target = new CircularBuffer<string>(3);  // Creates a buffer for storing up to 3 items
  target.Put("Alpha");                     // Head is 0, Tail is 1, Size is 1
  target.Put("Beta");                      // Head is 0, Tail is 2, Size is 2
  target.Put("Gamma");                     // Head is 0, Tail is 3, Size is 3
  target.Put("Delta");                     // Head is 1, Tail is 1, Size is 3

  firstItem = target.Get();                // firstItem is Beta. Head is 2, Tail is 1, Size is 2
  items = target.ToArray();                // items are Gamma, Delta. Head, Tail and Size are unchanged.

This final example shows how the buffer is unchanged when peeking.

  CircularBuffer<string> target;
  string firstItem;
  string lastItem;

  target = new CircularBuffer<string>(10); // Creates a buffer for storing up to 10 items
  target.Put("Alpha");                     // Head is 0, Tail is 1, Size is 1
  target.Put("Beta");                      // Head is 0, Tail is 2, Size is 2
  target.Put("Gamma");                     // Head is 0, Tail is 3, Size is 3
  target.Put("Delta");                     // Head is 0, Tail is 4, Size is 4

  firstItem = target.Peek();               // firstItem is Alpha. Head, Tail and Size are unchanged.
  lastItem = target.PeekLast();            // lastItem is Delta. Head, Tail and Size are unchanged.

For more examples, see the test class CircularBufferTests as this has tests which cover all the code paths. Except for ICollection.SyncRoot anyway!

Requirements

.NET Framework 2.0 or later.

Pre-built binaries are available via a signed NuGet package containing the following targets.

• .NET 3.5
• .NET 4.0
• .NET 4.5.2
• .NET 4.6.2
• .NET 4.7.2
• .NET 4.8
• .NET Standard 2.0
• .NET Standard 2.1
• .NET Core 2.1
• .NET Core 2.2
• .NET Core 3.1

Is there a target not on this list you'd like to see? Raise an issue, or even better, a pull request.

Acknowledgements

The CircularBuffer<T> class was originally taken from Circular Buffer for .NET, however I've fixed a number of bugs and added a few improvements. Unfortunately it didn't occur to me to keep a list of all the bugs I fixed.

Syntax-wise, I don't remember changing any method signatures so they should work the same. I did rename the AllowOverflow property to AllowOverwrite which seems to make more sense to me.

The only thing the original has that this version does not is localization support - the original version read exception messages from a resource file, whereas here they are just string literals.

See CONTRIBUTORS.md for further details of updates to the CircularBuffer<T> class.

License

The code is licensed under the New BSD License (BSD) as per the original source this implementation is based upon. See LICENSE.txt for details.