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diff --git a/gdbsupport/observable.h b/gdbsupport/observable.h
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+/* Observers
+
+   Copyright (C) 2016-2020 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/>.  */
+
+#ifndef COMMON_OBSERVABLE_H
+#define COMMON_OBSERVABLE_H
+
+#include <algorithm>
+#include <functional>
+#include <vector>
+
+namespace gdb
+{
+
+namespace observers
+{
+
+extern unsigned int observer_debug;
+
+/* An observer is an entity which is interested in being notified
+   when GDB reaches certain states, or certain events occur in GDB.
+   The entity being observed is called the observable.  To receive
+   notifications, the observer attaches a callback to the observable.
+   One observable can have several observers.
+
+   The observer implementation is also currently not reentrant.  In
+   particular, it is therefore not possible to call the attach or
+   detach routines during a notification.  */
+
+/* The type of a key that can be passed to attach, which can be passed
+   to detach to remove associated observers.  Tokens have address
+   identity, and are thus usually const globals.  */
+struct token
+{
+  token () = default;
+
+  DISABLE_COPY_AND_ASSIGN (token);
+};
+
+template<typename... T>
+class observable
+{
+public:
+
+  typedef std::function<void (T...)> func_type;
+
+  explicit observable (const char *name)
+    : m_name (name)
+  {
+  }
+
+  DISABLE_COPY_AND_ASSIGN (observable);
+
+  /* Attach F as an observer to this observable.  F cannot be
+     detached.  */
+  void attach (const func_type &f)
+  {
+    m_observers.emplace_back (nullptr, f);
+  }
+
+  /* Attach F as an observer to this observable.  T is a reference to
+     a token that can be used to later remove F.  */
+  void attach (const func_type &f, const token &t)
+  {
+    m_observers.emplace_back (&t, f);
+  }
+
+  /* Remove observers associated with T from this observable.  T is
+     the token that was previously passed to any number of "attach"
+     calls.  */
+  void detach (const token &t)
+  {
+    auto iter = std::remove_if (m_observers.begin (),
+				m_observers.end (),
+				[&] (const std::pair<const token *,
+				     func_type> &e)
+				{
+				  return e.first == &t;
+				});
+
+    m_observers.erase (iter, m_observers.end ());
+  }
+
+  /* Notify all observers that are attached to this observable.  */
+  void notify (T... args) const
+  {
+    if (observer_debug)
+      fprintf_unfiltered (gdb_stdlog, "observable %s notify() called\n",
+			  m_name);
+    for (auto &&e : m_observers)
+      e.second (args...);
+  }
+
+private:
+
+  std::vector<std::pair<const token *, func_type>> m_observers;
+  const char *m_name;
+};
+
+} /* namespace observers */
+
+} /* namespace gdb */
+
+#endif /* COMMON_OBSERVABLE_H */