Share Windows thread-suspend and -resume code

This adds "suspend" and "resume" methods to windows_thread_info, and
changes gdb and gdbserver to share this code.

gdb/ChangeLog
2020-04-08  Tom Tromey  <tromey@adacore.com>

	* windows-nat.c (thread_rec): Use windows_thread_info::suspend.
	(windows_continue): Use windows_continue::resume.
	* nat/windows-nat.h (struct windows_thread_info) <suspend,
	resume>: Declare new methods.
	* nat/windows-nat.c: New file.
	* configure.nat (NATDEPFILES): Add nat/windows-nat.o when needed.

gdbserver/ChangeLog
2020-04-08  Tom Tromey  <tromey@adacore.com>

	* win32-low.c (win32_require_context, suspend_one_thread): Use
	windows_thread_info::suspend.
	(continue_one_thread): Use windows_thread_info::resume.
	* configure.srv (srv_tgtobj): Add windows-nat.o when needed.

2 files changed, 66 insertions, 0 deletions

diff --git a/gdb/nat/windows-nat.c b/gdb/nat/windows-nat.c
new file mode 100644
index 0000000..a98ff42
--- /dev/null
+++ b/gdb/nat/windows-nat.c
@@ -0,0 +1,60 @@
+/* Internal interfaces for the Windows code
+   Copyright (C) 1995-2019 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include "gdbsupport/common-defs.h"
+#include "nat/windows-nat.h"
+
+void
+windows_thread_info::suspend ()
+{
+  if (suspended != 0)
+    return;
+
+  if (SuspendThread (h) == (DWORD) -1)
+    {
+      DWORD err = GetLastError ();
+
+      /* We get Access Denied (5) when trying to suspend
+	 threads that Windows started on behalf of the
+	 debuggee, usually when those threads are just
+	 about to exit.
+	 We can get Invalid Handle (6) if the main thread
+	 has exited.  */
+      if (err != ERROR_INVALID_HANDLE && err != ERROR_ACCESS_DENIED)
+	warning (_("SuspendThread (tid=0x%x) failed. (winerr %u)"),
+		 (unsigned) tid, (unsigned) err);
+      suspended = -1;
+    }
+  else
+    suspended = 1;
+}
+
+void
+windows_thread_info::resume ()
+{
+  if (suspended > 0)
+    {
+      if (ResumeThread (h) == (DWORD) -1)
+	{
+	  DWORD err = GetLastError ();
+	  warning (_("warning: ResumeThread (tid=0x%x) failed. (winerr %u)"),
+		   (unsigned) tid, (unsigned) err);
+	}
+    }
+  suspended = 0;
+}
diff --git a/gdb/nat/windows-nat.h b/gdb/nat/windows-nat.h
index 543de89..695f801 100644
--- a/gdb/nat/windows-nat.h
+++ b/gdb/nat/windows-nat.h
@@ -34,6 +34,12 @@ struct windows_thread_info
 
   DISABLE_COPY_AND_ASSIGN (windows_thread_info);
 
+  /* Ensure that this thread has been suspended.  */
+  void suspend ();
+
+  /* Resume the thread if it has been suspended.  */
+  void resume ();
+
   /* The Win32 thread identifier.  */
   DWORD tid;