Option to add child as indeterminate progress bar

src/ShellProgressBar.Example/Examples/IndeterminateChildrenNoCollapse.cs

@@ -0,0 +1,40 @@
+using System;
+using System.Threading;
+
+namespace ShellProgressBar.Example.Examples
+{
+	public class IndeterminateChildrenNoCollapseExample : ExampleBase
+	{
+		protected override void Start()
+		{
+			const int totalChildren = 10;
+			Random random = new Random();
+			var options = new ProgressBarOptions
+			{
+				ForegroundColor = ConsoleColor.Yellow,
+				BackgroundColor = ConsoleColor.DarkGray,
+				ProgressCharacter = '─'
+			};
+			var childOptions = new ProgressBarOptions
+			{
+				ForegroundColor = ConsoleColor.Green,
+				BackgroundColor = ConsoleColor.DarkGray,
+				ProgressCharacter = '─',
+				CollapseWhenFinished = false
+			};
+			using (var pbar = new ProgressBar(totalChildren, "main progressbar", options))
+			{
+				for (int i = 1; i <= totalChildren; i++)
+				{
+					pbar.Message = $"Start {i} of {totalChildren}: main progressbar";
+					using (var child = pbar.SpawnIndeterminate("child action " + i, childOptions))
+					{
+						Thread.Sleep(1000 * random.Next(5, 15));
+						child.Finished();
+					}
+					pbar.Tick();
+				}
+			}
+		}
+	}
+}

src/ShellProgressBar.Example/Program.cs

@@ -27,6 +27,7 @@ class Program
 			new NeverTicksExample(),
 			new EstimatedDurationExample(),
 			new IndeterminateProgressExample(),
+			new IndeterminateChildrenNoCollapseExample(),
 		};
 
 		private static readonly IList<IProgressBarExample> Examples = new List<IProgressBarExample>

src/ShellProgressBar/IndeterminateChildProgressBar.cs

@@ -0,0 +1,61 @@
+using System;
+using System.Collections.Concurrent;
+using System.Threading;
+
+namespace ShellProgressBar
+{
+	public class IndeterminateChildProgressBar : ChildProgressBar
+	{
+		private const int MaxTicksForIndeterminate = 20;
+		private Timer _timer;
+		internal IndeterminateChildProgressBar(
+			string message,
+			Action scheduleDraw,
+			Action<string> writeLine,
+			Action<string> writeError,
+			ProgressBarOptions options = null,
+			Action<ProgressBarHeight> growth = null
+		)
+			: base(MaxTicksForIndeterminate, message, scheduleDraw, writeLine, writeError, options, growth)
+		{
+			if (options == null)
+			{
+				options = new ProgressBarOptions();
+			}
+
+			options.DisableBottomPercentage = true;
+			_timer = new Timer((s) => OnTimerTick(), null, 500, 500);
+		}
+
+		private long _seenTicks = 0;
+
+		protected void OnTimerTick()
+		{
+			Interlocked.Increment(ref _seenTicks);
+			if (_seenTicks == MaxTicksForIndeterminate - 1)
+			{
+				this.Tick(0);
+				Interlocked.Exchange(ref _seenTicks, 0);
+			}
+			else
+			{
+				this.Tick();
+			}
+			DisplayProgress();
+		}
+
+		public void Finished()
+		{
+			_timer.Change(Timeout.Infinite, Timeout.Infinite);
+			_timer.Dispose();
+			Tick(MaxTicksForIndeterminate);
+		}
+
+		public void Dispose()
+		{
+			if (_timer != null) _timer.Dispose();
+			foreach (var c in this.Children) c.Dispose();
+			OnDone();
+		}
+	}
+}

src/ShellProgressBar/ProgressBarBase.cs

@@ -108,6 +108,20 @@ public ChildProgressBar Spawn(int maxTicks, string message, ProgressBarOptions o
 			return pbar;
 		}
 
+		public IndeterminateChildProgressBar SpawnIndeterminate(string message, ProgressBarOptions options = null)
+		{
+			// if this bar collapses all child progressbar will collapse
+			if (options?.CollapseWhenFinished == false && this.Options.CollapseWhenFinished)
+				options.CollapseWhenFinished = true;
+
+			var pbar = new IndeterminateChildProgressBar(
+				message, DisplayProgress, WriteLine, WriteErrorLine, options ?? this.Options, d => this.Grow(d)
+			);
+			this.Children.Add(pbar);
+			DisplayProgress();
+			return pbar;
+		}
+
 		public abstract void WriteLine(string message);
 		public abstract void WriteErrorLine(string message);