Update libraries for preview 7

release-notes/10.0/preview/preview7/libraries.md

@@ -11,3 +11,84 @@ Here's a summary of what's new in .NET Libraries in this preview release:
 ## Feature
 
 Something about the feature
+
+## Launch Windows processes in new process group
+
+For Windows, you can now use `ProcessStartInfo.CreateNewProcessGroup` to launch a process in a separate PG.  This allows you to send isolated signals to child processes which could otherwise take down the parent without proper handling.  Sending signals is convenient to avoid forceful termination.
+
+```csharp
+using System;
+using System.Diagnostics;
+using System.IO;
+using System.Runtime.InteropServices;
+using System.Threading;
+
+class Program
+{
+    static void Main(string[] args)
+    {
+        bool isChildProcess = args.Length > 0 && args[0] == "child";
+        if (!isChildProcess)
+        {
+            var psi = new ProcessStartInfo
+            {
+                FileName = Environment.ProcessPath,
+                Arguments = "child",
+                CreateNewProcessGroup = true,
+            };
+
+            using Process process = Process.Start(psi)!;
+            Thread.Sleep(5_000);
+
+            GenerateConsoleCtrlEvent(CTRL_C_EVENT, (uint)process.Id);
+            process.WaitForExit();
+
+            Console.WriteLine("Child process terminated gracefully, continue with the parent process logic if needed.");
+        }
+        else
+        {
+            // you need to call SetConsoleCtrlHandler this way if you want to handle Ctrl+C in the child process,
+            // see https://learn.microsoft.com/windows/win32/api/processthreadsapi/nf-processthreadsapi-createprocessw#remarks
+            SetConsoleCtrlHandler((IntPtr)null, false);
+
+            Console.WriteLine("Greetings from the child process!  I need to be gracefully terminated, send me a signal!");
+
+            bool stop = false;
+
+            var registration = PosixSignalRegistration.Create(PosixSignal.SIGINT, ctx =>
+            {
+                stop = true;
+                ctx.Cancel = true;
+                Console.WriteLine("Received CTRL+C, stopping...");
+            });
+
+            StreamWriter sw = File.AppendText("log.txt");
+            int i = 0;
+            while (!stop)
+            {
+                Thread.Sleep(1000);
+                sw.WriteLine($"{++i}");
+                Console.WriteLine($"Logging {i}...");
+            }
+
+            // Clean up
+            sw.Dispose();
+            registration.Dispose();
+
+            Console.WriteLine("Thanks for not killing me!");
+        }
+    }
+
+    private const int CTRL_C_EVENT = 0;
+    private const int CTRL_BREAK_EVENT = 1;
+
+    [DllImport("kernel32.dll", SetLastError = true)]
+    [return: MarshalAs(UnmanagedType.Bool)]
+    private static extern bool SetConsoleCtrlHandler(IntPtr handler, [MarshalAs(UnmanagedType.Bool)] bool Add);
+
+    [DllImport("kernel32.dll", SetLastError = true)]
+    [return: MarshalAs(UnmanagedType.Bool)]
+    private static extern bool GenerateConsoleCtrlEvent(uint dwCtrlEvent, uint dwProcessGroupId);
+}
+```
+