AU: Catch terminate signals and block exit if necessary.

terminator.h

Index: terminator.h
diff --git a/terminator.h b/terminator.h
new file mode 100644
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+++ b/terminator.h
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+// Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROMEOS_PLATFORM_UPDATE_ENGINE_TERMINATOR_H__
+#define CHROMEOS_PLATFORM_UPDATE_ENGINE_TERMINATOR_H__
+
+#include <signal.h>
+
+namespace chromeos_update_engine {
+
+// A class allowing graceful delayed exit.
+class Terminator {
+ public:
+  // Initializes the terminator and sets up signal handlers.
+  static void Init();
+
+  // Terminates the current process.
+  static void Exit();
+
+  // Set to true if the terminator should block termination requests in an
+  // attempt to block exiting.
+  static void set_exit_blocked(bool block) { exit_blocked_ = block ? 1 : 0; }
+
+  // Returns true if the system is trying to terminate the process, false
+  // otherwise. Returns true only if exit was blocked when the termination
+  // request arrived.
+  static bool exit_requested() { return exit_requested_ != 0; }
+
+ private:
+  // The signal handler.
+  static void HandleSignal(int signum);
+
+  static volatile sig_atomic_t exit_blocked_;
+  static volatile sig_atomic_t exit_requested_;
+};
+
+class ScopedTerminatorExitUnblocker {
+ public:
+  ~ScopedTerminatorExitUnblocker();
+};
+
+}  // namespace chromeos_update_engine
+
+#endif  // CHROMEOS_PLATFORM_UPDATE_ENGINE_TERMINATOR_H__