Crash guard: prevent loading of preset if it has caused crashes.

src/CrashGuard.hpp

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+/*
+ *   Copyright (c) 2025 Robin E. R. Davies
+ *   All rights reserved.
+
+ *   Permission is hereby granted, free of charge, to any person obtaining a copy
+ *   of this software and associated documentation files (the "Software"), to deal
+ *   in the Software without restriction, including without limitation the rights
+ *   to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ *   copies of the Software, and to permit persons to whom the Software is
+ *   furnished to do so, subject to the following conditions:
+
+ *   The above copyright notice and this permission notice shall be included in all
+ *   copies or substantial portions of the Software.
+
+ *   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ *   IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ *   FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ *   AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ *   LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ *   OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ *   SOFTWARE.
+ */
+
+#pragma once
+
+#include <mutex>
+#include <atomic>
+#include <filesystem>
+
+namespace pipedal
+{
+
+    /**
+     * @brief Crash protection.
+     *
+     * Detect the situation where PiPedal has crashed multiple times due to SIG_SEGVS caused by a plugin.
+     *
+     * The basic premise: mark segments of code as "crash protected". If Pipedal shuts down without exiting the
+     * crash guard zone for some fixed number of occasions (3?), then set a flag that will prevent
+     * loading of the default plugin when PiPedal next loads. Since PiPedal restarts indefinitely while
+     * running as a service, this allows users to recover after they have committed a plugin that crashes
+     * into their current preset.
+     *
+     */
+
+    class CrashGuard
+    {
+    public:
+        static void SetCrashGuardFileName(const std::filesystem::path &path);
+        static bool HasCrashed();
+        static void ClearCrashFlag();
+
+        static void EnterCrashGuardZone();
+        static void LeaveCrashGuardZone();
+
+    private:
+        static int crashCount;
+        static std::mutex mutex;
+        static std::filesystem::path fileName;
+        static int64_t depth;
+    };
+
+    class CrashGuardLock {
+    public:
+        CrashGuardLock() {
+            CrashGuard::EnterCrashGuardZone();
+        }
+        ~CrashGuardLock() {
+            CrashGuard::LeaveCrashGuardZone();
+        }
+        CrashGuardLock(const CrashGuardLock &) = delete;
+        CrashGuardLock &operator=(const CrashGuardLock &) = delete;
+        CrashGuardLock(CrashGuardLock &&) = delete;
+        CrashGuardLock &operator=(CrashGuardLock &&) = delete;
+    };
+};