Introduce fetch_pending_stop

This introduces a new "fetch_pending_stop" function and changes gdb to
use it.  This function removes the first matching pending stop from
the list of such stops.

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

	* windows-nat.c (get_windows_debug_event): Use
	fetch_pending_stop.
	* nat/windows-nat.h (fetch_pending_stop): Declare.
	* nat/windows-nat.c (fetch_pending_stop): New function.

gdb/ChangeLog

@@ -1,3 +1,10 @@
+2020-04-08  Tom Tromey  <tromey@adacore.com>
+
+	* windows-nat.c (get_windows_debug_event): Use
+	fetch_pending_stop.
+	* nat/windows-nat.h (fetch_pending_stop): Declare.
+	* nat/windows-nat.c (fetch_pending_stop): New function.
+
 2020-04-08  Tom Tromey  <tromey@adacore.com>
 
 	* windows-nat.c (windows_continue): Use matching_pending_stop and

gdb/nat/windows-nat.c

@@ -343,6 +343,34 @@ matching_pending_stop (bool debug_events)
 
 /* See nat/windows-nat.h.  */
 
+gdb::optional<pending_stop>
+fetch_pending_stop (bool debug_events)
+{
+  gdb::optional<pending_stop> result;
+  for (auto iter = pending_stops.begin ();
+       iter != pending_stops.end ();
+       ++iter)
+    {
+      if (desired_stop_thread_id == -1
+	  || desired_stop_thread_id == iter->thread_id)
+	{
+	  result = *iter;
+	  current_event = iter->event;
+
+	  DEBUG_EVENTS (("get_windows_debug_event - "
+			 "pending stop found in 0x%x (desired=0x%x)\n",
+			 iter->thread_id, desired_stop_thread_id));
+
+	  pending_stops.erase (iter);
+	  break;
+	}
+    }
+
+  return result;
+}
+
+/* See nat/windows-nat.h.  */
+
 BOOL
 continue_last_debug_event (DWORD continue_status, bool debug_events)
 {

gdb/nat/windows-nat.h

@@ -22,6 +22,7 @@
 #include <windows.h>
 #include <vector>
 
+#include "gdbsupport/gdb_optional.h"
 #include "target/waitstatus.h"
 
 namespace windows_nat
@@ -231,6 +232,12 @@ extern handle_exception_result handle_exception
 
 extern bool matching_pending_stop (bool debug_events);
 
+/* See if a pending stop matches DESIRED_STOP_THREAD_ID.  If so,
+   remove it from the list of pending stops, set 'current_event', and
+   return it.  Otherwise, return an empty optional.  */
+
+extern gdb::optional<pending_stop> fetch_pending_stop (bool debug_events);
+
 /* A simple wrapper for ContinueDebugEvent that continues the last
    waited-for event.  If DEBUG_EVENTS is true, logging will be
    enabled.  */

gdb/windows-nat.c

@@ -1522,29 +1522,18 @@ windows_nat_target::get_windows_debug_event (int pid,
   /* If there is a relevant pending stop, report it now.  See the
      comment by the definition of "pending_stops" for details on why
      this is needed.  */
-  for (auto iter = pending_stops.begin ();
-       iter != pending_stops.end ();
-       ++iter)
+  gdb::optional<pending_stop> stop = fetch_pending_stop (debug_events);
+  if (stop.has_value ())
     {
-      if (desired_stop_thread_id == -1
-	  || desired_stop_thread_id == iter->thread_id)
-	{
-	  thread_id = iter->thread_id;
-	  *ourstatus = iter->status;
-	  current_event = iter->event;
+      thread_id = stop->thread_id;
+      *ourstatus = stop->status;
 
-	  inferior_ptid = ptid_t (current_event.dwProcessId, thread_id, 0);
-	  current_windows_thread = thread_rec (inferior_ptid,
-					       INVALIDATE_CONTEXT);
-	  current_windows_thread->reload_context = 1;
+      inferior_ptid = ptid_t (current_event.dwProcessId, thread_id, 0);
+      current_windows_thread = thread_rec (inferior_ptid,
+					   INVALIDATE_CONTEXT);
+      current_windows_thread->reload_context = 1;
 
-	  DEBUG_EVENTS (("get_windows_debug_event - "
-			 "pending stop found in 0x%x (desired=0x%x)\n",
-			 thread_id, desired_stop_thread_id));
-
-	  pending_stops.erase (iter);
-	  return thread_id;
-	}
+      return thread_id;
     }
 
   last_sig = GDB_SIGNAL_0;