win: os_proc_tree_kill()

XXX: comment at https://stackoverflow.com/q/1173342 :
> Windows recycles PIDs quite fast, you have to be extra careful not
> to kill unrelated processes. These APIs will report PPIDs for long
> dead processes whose PIDs may have been recycled. Check the parent
> start date to make sure it is related to the processes you spawned.

src/nvim/event/process.c

@@ -12,6 +12,7 @@
 #include "nvim/event/wstream.h"
 #include "nvim/event/process.h"
 #include "nvim/event/libuv_process.h"
+#include "nvim/os/process.h"
 #include "nvim/os/pty_process.h"
 #include "nvim/globals.h"
 #include "nvim/macros.h"
@@ -201,23 +202,6 @@ int process_wait(Process *proc, int ms, MultiQueue *events)
   return proc->status;
 }
 
-/// Kills a process and its descendants.
-static void os_proc_tree_kill(int pid, int sig) {
-  assert(sig == SIGTERM || sig == SIGKILL);
-  int pgid = getpgid(pid);
-  if (pgid > 0) {  // Ignore error. Never kill self (pid=0).
-    if (pgid == pid) {
-      ILOG("sending %s to process group: -%d",
-           sig == SIGTERM ? "SIGTERM" : "SIGKILL",
-           pgid);
-      uv_kill(-pgid, sig);
-    } else {
-      // Should never happen, because process_spawn() did setsid() in the child.
-      ELOG("pgid %d != pid %d", pgid, pid);
-    }
-  }
-}
-
 /// Ask a process to terminate and eventually kill if it doesn't respond
 void process_stop(Process *proc) FUNC_ATTR_NONNULL_ALL
 {

src/nvim/os/process.c

@@ -0,0 +1,87 @@
+// This is an open source non-commercial project. Dear PVS-Studio, please check
+// it. PVS-Studio Static Code Analyzer for C, C++ and C#: http://www.viva64.com
+
+#include <uv.h>  // for HANDLE (win32)
+#ifdef WIN32
+# include <tlhelp32.h>  // for CreateToolhelp32Snapshot
+#endif
+
+#include "nvim/log.h"
+#include "nvim/os/process.h"
+#include "nvim/os/os.h"
+#include "nvim/os/os_defs.h"
+
+#ifdef INCLUDE_GENERATED_DECLARATIONS
+# include "os/process.c.generated.h"
+#endif
+
+#ifdef WIN32
+/// Kills process `pid` and its descendants recursively.
+bool os_proc_tree_kill_rec(HANDLE process, int sig)
+{
+  if (process == NULL) {
+    return false;
+  }
+  PROCESSENTRY32 pe;
+  DWORD pid = GetProcessId(process);
+
+  if (pid != 0) {
+    HANDLE h = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0);
+    if (h != INVALID_HANDLE_VALUE) {
+      pe.dwSize = sizeof(PROCESSENTRY32);
+      if (!Process32First(h, &pe)) {
+        goto theend;
+      }
+
+      do {
+        if (pe.th32ParentProcessID == pid) {
+          HANDLE ph = OpenProcess(PROCESS_ALL_ACCESS, FALSE, pe.th32ProcessID);
+          if (ph != NULL) {
+            os_proc_tree_kill_rec(ph, sig);
+            CloseHandle(ph);
+          }
+        }
+      } while (Process32Next(h, &pe));
+
+      CloseHandle(h);
+    }
+  }
+
+theend:
+  return (bool)TerminateProcess(process, (unsigned int)sig);
+}
+bool os_proc_tree_kill(int pid, int sig)
+{
+  assert(sig >= 0);
+  assert(sig == SIGTERM || sig == SIGKILL);
+  if (pid > 0) {
+    ILOG("terminating process tree: %d", pid);
+    HANDLE h = OpenProcess(PROCESS_ALL_ACCESS, FALSE, (DWORD)pid);
+    return os_proc_tree_kill_rec(h, sig);
+  } else {
+    ELOG("invalid pid: %d", pid);
+  }
+  return false;
+}
+#else
+/// Kills process group where `pid` is the process group leader.
+bool os_proc_tree_kill(int pid, int sig)
+{
+  assert(sig == SIGTERM || sig == SIGKILL);
+  int pgid = getpgid(pid);
+  if (pgid > 0) {  // Ignore error. Never kill self (pid=0).
+    if (pgid == pid) {
+      ILOG("sending %s to process group: -%d",
+           sig == SIGTERM ? "SIGTERM" : "SIGKILL", pgid);
+      int rv = uv_kill(-pgid, sig);
+      return rv == 0;
+    } else {
+      // Should never happen, because process_spawn() did setsid() in the child.
+      ELOG("pgid %d != pid %d", pgid, pid);
+    }
+  } else {
+    ELOG("getpgid(%d) returned %d", pid, pgid);
+  }
+  return false;
+}
+#endif

src/nvim/os/process.h

@@ -0,0 +1,8 @@
+#ifndef NVIM_OS_PROCESS_H
+#define NVIM_OS_PROCESS_H
+
+#ifdef INCLUDE_GENERATED_DECLARATIONS
+# include "os/process.h.generated.h"
+#endif
+
+#endif  // NVIM_OS_PROCESS_H