Replace ProcessUtilities.SendPosixSignal with SafeProcessHandle.Signal API

src/Dotnet.Watch/Watch/Process/ProcessRunner.cs

@@ -1,7 +1,9 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.ComponentModel;
 using System.Diagnostics;
+using System.Runtime.Versioning;
 using Microsoft.Extensions.Logging;
 
 namespace Microsoft.DotNet.Watch;
@@ -328,7 +330,7 @@ private static void TerminateProcess(Process process, ProcessState state, ILogge
                 }
                 else
                 {
-                    TerminateUnixProcess(state, logger, force);
+                    TerminateUnixProcess(process, state, logger, force);
                 }
             }
         }
@@ -364,12 +366,26 @@ private static void TerminateWindowsProcess(Process process, ProcessState state,
         }
     }
 
-    private static void TerminateUnixProcess(ProcessState state, ILogger logger, bool force)
+    [UnsupportedOSPlatform("windows")]
+    private static void TerminateUnixProcess(Process process, ProcessState state, ILogger logger, bool force)
     {
+        var signal = force ? PosixSignal.SIGKILL : PosixSignal.SIGTERM;
         var signalName = force ? "SIGKILL" : "SIGTERM";
         logger.Log(MessageDescriptor.TerminatingProcess, state.ProcessId, signalName);
 
-        var error = ProcessUtilities.SendPosixSignal(state.ProcessId, signal: force ? ProcessUtilities.SIGKILL : ProcessUtilities.SIGTERM);
+        string? error = null;
+        try
+        {
+            process.SafeHandle.Signal(signal);
+        }
+        catch (Win32Exception ex)
+        {
+            // A process that has already exited is handled by Signal's non-exception return path.
+            // This catch is for exceptional failures, such as attempting to signal a process
+            // that we don't have permission to kill.
+            error = ex.Message;
+        }
+
         if (error != null)
         {
             logger.Log(MessageDescriptor.FailedToSendSignalToProcess, signalName, state.ProcessId, error);

src/Dotnet.Watch/Watch/UI/PhysicalConsole.cs

@@ -1,6 +1,9 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.ComponentModel;
+using System.Diagnostics;
+
 namespace Microsoft.DotNet.Watch;
 
 internal sealed class PhysicalConsole : IConsole
@@ -55,7 +58,23 @@ private async Task ListenToStandardInputAsync()
                     else
                     {
                         Console.WriteLine($"Sending SIGTERM to {processId}");
-                        error = ProcessUtilities.SendPosixSignal(processId, ProcessUtilities.SIGTERM);
+                        error = null;
+                        try
+                        {
+                            using var process = Process.GetProcessById(processId);
+                            process.SafeHandle.Signal(PosixSignal.SIGTERM);
+                        }
+                        catch (Win32Exception ex)
+                        {
+                            // Signal returns false when the given process has already exited.
+                            // So it can throw only when we try to kill a non-child process
+                            // that we don't have permission to kill.
+                            error = ex.Message;
+                        }
+                        catch (ArgumentException)
+                        {
+                            // Process has already exited
+                        }
                     }
 
                     if (error != null)

src/Dotnet.Watch/Watch/Utilities/ProcessUtilities.cs

@@ -5,9 +5,6 @@ namespace Microsoft.DotNet.Watch;
 
 internal static class ProcessUtilities
 {
-    public const int SIGKILL = 9;
-    public const int SIGTERM = 15;
-
     public static string? SendWindowsCtrlCEvent(int processId)
     {
         const uint CTRL_C_EVENT = 0;
@@ -28,14 +25,6 @@ internal static class ProcessUtilities
         static extern bool GenerateConsoleCtrlEvent(uint dwCtrlEvent, uint dwProcessGroupId);
     }
 
-    public static string? SendPosixSignal(int processId, int signal)
-    {
-        return sys_kill(processId, signal) == 0 ? null : GetLastPInvokeErrorMessage();
-
-        [DllImport("libc", SetLastError = true, EntryPoint = "kill")]
-        static extern int sys_kill(int pid, int sig);
-    }
-
     private static string GetLastPInvokeErrorMessage()
     {
         var error = Marshal.GetLastPInvokeError();