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diff --git a/indra/llcommon/llwatchdog.h b/indra/llcommon/llwatchdog.h
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+/**
+ * @file llthreadwatchdog.h
+ * @brief The LLThreadWatchdog class declaration
+ *
+ * $LicenseInfo:firstyear=2007&license=viewerlgpl$
+ * Second Life Viewer Source Code
+ * Copyright (C) 2010, Linden Research, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation;
+ * version 2.1 of the License only.
+ *
+ * This library 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * Linden Research, Inc., 945 Battery Street, San Francisco, CA  94111  USA
+ * $/LicenseInfo$
+ */
+
+#ifndef LL_LLTHREADWATCHDOG_H
+#define LL_LLTHREADWATCHDOG_H
+
+#ifndef LL_TIMER_H
+    #include "lltimer.h"
+#endif
+#include "llmutex.h"
+#include "llsingleton.h"
+
+#include <functional>
+
+// LLWatchdogEntry is the interface used by the tasks that
+// need to be watched.
+class LLWatchdogEntry
+{
+public:
+    LLWatchdogEntry(const std::string &thread_name);
+    virtual ~LLWatchdogEntry();
+
+    // isAlive is accessed by the watchdog thread.
+    // This may mean that resources used by
+    // isAlive and other method may need synchronization.
+    virtual bool isAlive() const = 0;
+    virtual void reset() = 0;
+    virtual void start();
+    virtual void stop();
+    virtual std::string getLastState() const { return std::string(); }
+    typedef std::thread::id id_t;
+    std::string getThreadName() const;
+
+private:
+    id_t mThreadID; // ID of the thread being watched
+    std::string mThreadName;
+};
+
+class LLWatchdogTimeout : public LLWatchdogEntry
+{
+public:
+    LLWatchdogTimeout(const std::string& thread_name);
+    virtual ~LLWatchdogTimeout();
+
+    bool isAlive() const override;
+    void reset() override;
+    void start() override { start(""); }
+    void stop() override;
+
+    void start(std::string_view state);
+    void setTimeout(F32 d);
+    void ping(std::string_view state);
+    const std::string& getState() {return mPingState; }
+    std::string getLastState() const override { return mPingState; }
+
+private:
+    LLTimer mTimer;
+    F32 mTimeout;
+    std::string mPingState;
+};
+
+class LLWatchdogTimerThread; // Defined in the cpp
+class LLWatchdog : public LLSingleton<LLWatchdog>
+{
+    LLSINGLETON(LLWatchdog);
+    ~LLWatchdog();
+
+public:
+    // Add an entry to the watchdog.
+    void add(LLWatchdogEntry* e);
+    void remove(LLWatchdogEntry* e);
+
+    typedef std::function<void()> func_t;
+    void init(func_t set_error_state_callback);
+    void run();
+    void cleanup();
+
+
+private:
+    void lockThread();
+    void unlockThread();
+
+    typedef std::set<LLWatchdogEntry*> SuspectsRegistry;
+    SuspectsRegistry mSuspects;
+    LLMutex* mSuspectsAccessMutex;
+    LLWatchdogTimerThread* mTimer;
+    U64 mLastClockCount;
+
+    // At the moment watchdog expects app to set markers in mCreateMarkerFnc,
+    // but technically can be used to set any error states or do some cleanup
+    // or show warnings.
+    func_t mCreateMarkerFnc;
+};
+
+#endif // LL_LLTHREADWATCHDOG_H