feat(windows): suspend entire process tree

Suspend / resume child processes recursively on
Windows, the same as we do on Linux. Improves
reliability and performance gains for processes
that spawn many child processes.

lib/native_platform/src/process/repository/src/win32/win32.dart

@@ -0,0 +1,53 @@
+// ignore_for_file: non_constant_identifier_names, constant_identifier_names
+
+import 'dart:convert';
+import 'dart:ffi';
+
+final _kernel32 = DynamicLibrary.open('kernel32.dll');
+
+final CreateToolhelp32Snapshot =
+    _kernel32.lookupFunction<IntPtr Function(Uint32, Uint32), int Function(int, int)>(
+        'CreateToolhelp32Snapshot');
+
+final Process32First = _kernel32.lookupFunction<
+    Int32 Function(IntPtr hSnapshot, Pointer<PROCESSENTRY32> lppe),
+    int Function(int hSnapshot, Pointer<PROCESSENTRY32> lppe)>('Process32First');
+
+final Process32Next = _kernel32.lookupFunction<
+    Int32 Function(IntPtr hSnapshot, Pointer<PROCESSENTRY32> lppe),
+    int Function(int hSnapshot, Pointer<PROCESSENTRY32> lppe)>('Process32Next');
+
+final class PROCESSENTRY32 extends Struct {
+  @Int32()
+  external int dwSize;
+  @Int32()
+  external int cntUsage;
+  @Int32()
+  external int th32ProcessID;
+  external Pointer<Uint32> th32DefaultHeapID;
+  @Int32()
+  external int th32ModuleID;
+  @Int32()
+  external int cntThreads;
+  @Int32()
+  external int th32ParentProcessID;
+  @Int32()
+  external int pcPriClassBase;
+  @Int32()
+  external int dwFlags;
+  @Array(260)
+  external Array<Uint8> _szExeFile;
+  String get szExeFile => _unwrap(_szExeFile);
+}
+
+String _unwrap(Array<Uint8> bytes) {
+  String buf = "";
+  int i = 0;
+  while (bytes[i] != 0) {
+    buf += utf8.decode([bytes[i]]);
+    i += 1;
+  }
+  return buf;
+}
+
+const TH32CS_SNAPPROCESS = 0x00000002;

lib/native_platform/src/process/repository/src/win32_process_repository.dart

@@ -7,6 +7,7 @@ import 'package:win32_suspend_process/win32_suspend_process.dart';
 
 import '../../../../../logs/logs.dart';
 import '../../process.dart';
+import 'win32/win32.dart';
 
 /// Provides interaction access with host system processes on Windows.
 class Win32ProcessRepository extends ProcessRepository {
@@ -101,6 +102,15 @@ class Win32ProcessRepository extends ProcessRepository {
     final successful = (result == 0);
     log.i('Resuming $pid was successful: $successful');
     CloseHandle(processHandle);
+
+    if (successful) {
+      // Resume child processes recursively.
+      final childPids = await _getChildProcesses(pid);
+      for (final childPid in childPids) {
+        await resume(childPid);
+      }
+    }
+
     return successful;
   }
 
@@ -116,9 +126,46 @@ class Win32ProcessRepository extends ProcessRepository {
     final successful = (result == 0);
     log.i('Suspending $pid was successful: $successful');
     CloseHandle(processHandle);
+
+    if (successful) {
+      // Suspend child processes recursively.
+      final childPids = await _getChildProcesses(pid);
+      for (final childPid in childPids) {
+        await suspend(childPid);
+      }
+    }
+
     return successful;
   }
 
+  /// Returns a list of child processes for the provided [pid].
+  Future<List<int>> _getChildProcesses(int pid) async {
+    final childPids = <int>[];
+    final snapshot = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0);
+    if (snapshot == INVALID_HANDLE_VALUE) {
+      log.w('Failed to create snapshot: ${GetLastError()}');
+      return childPids;
+    }
+
+    final processEntry = calloc<PROCESSENTRY32>();
+    processEntry.ref.dwSize = sizeOf<PROCESSENTRY32>();
+
+    final isProcessFound = Process32First(snapshot, processEntry) == TRUE;
+    if (isProcessFound) {
+      do {
+        if (processEntry.ref.th32ParentProcessID == pid) {
+          childPids.add(processEntry.ref.th32ProcessID);
+        }
+      } while (Process32Next(snapshot, processEntry) == TRUE);
+    } else {
+      log.w('Failed to retrieve first process: ${GetLastError()}');
+    }
+
+    CloseHandle(snapshot);
+    calloc.free(processEntry);
+    return childPids;
+  }
+
   /// Returns true if the process is suspended, false otherwise.
   bool _isProcessSuspended(int pid) {
     return _isProcessSuspendedNative(pid) == 1;