1 files changed, 138 insertions, 0 deletions
diff --git a/indra/llcommon/throttle.h b/indra/llcommon/throttle.h
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+++ b/indra/llcommon/throttle.h
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+/**
+ * @file   throttle.h
+ * @author Nat Goodspeed
+ * @date   2024-08-12
+ * @brief  Throttle class
+ * 
+ * $LicenseInfo:firstyear=2024&license=viewerlgpl$
+ * Copyright (c) 2024, Linden Research, Inc.
+ * $/LicenseInfo$
+ */
+
+#if ! defined(LL_THROTTLE_H)
+#define LL_THROTTLE_H
+
+#include "apply.h"                  // LL::bind_front()
+#include "llerror.h"
+#include <functional>
+#include <iomanip>                  // std::quoted()
+
+class ThrottleBase
+{
+public:
+    ThrottleBase(F64 interval):
+        mInterval(interval)
+    {}
+
+protected:
+    bool too_fast();                // not const: we update mNext
+    F64 mInterval, mNext{ 0. };
+};
+
+/**
+ * An instance of Throttle mediates calls to some other specified function,
+ * ensuring that it's called no more often than the specified time interval.
+ * Throttle is an abstract base class that delegates the behavior when the
+ * specified interval is exceeded.
+ */
+template <typename SIGNATURE>
+class Throttle: public ThrottleBase
+{
+public:
+    Throttle(const std::string& desc,
+             const std::function<SIGNATURE>& func,
+             F64 interval):
+        ThrottleBase(interval),
+        mDesc(desc),
+        mFunc(func)
+    {}
+    // Constructing Throttle with a member function pointer but without an
+    // instance pointer requires you to pass the instance pointer/reference as
+    // the first argument to operator()().
+    template <typename R, class C>
+    Throttle(const std::string& desc, R C::* method, F64 interval):
+        Throttle(desc, std::mem_fn(method), interval)
+    {}
+    template <typename R, class C>
+    Throttle(const std::string& desc, R C::* method, C* instance, F64 interval):
+        Throttle(desc, LL::bind_front(method, instance), interval)
+    {}
+    template <typename R, class C>
+    Throttle(const std::string& desc, R C::* method, const C* instance, F64 interval):
+        Throttle(desc, LL::bind_front(method, instance), interval)
+    {}
+    virtual ~Throttle() {}
+
+    template <typename... ARGS>
+    auto operator()(ARGS... args)
+    {
+        if (too_fast())
+        {
+            suppress();
+            using rtype = decltype(mFunc(std::forward<ARGS>(args)...));
+            if constexpr (! std::is_same_v<rtype, void>)
+            {
+                return rtype{};
+            }
+        }
+        else
+        {
+            return mFunc(std::forward<ARGS>(args)...);
+        }
+    }
+
+protected:
+    // override with desired behavior when calls come too often
+    virtual void suppress() = 0;
+    const std::string mDesc;
+
+private:
+    std::function<SIGNATURE> mFunc;
+};
+
+/**
+ * An instance of LogThrottle mediates calls to some other specified function,
+ * ensuring that it's called no more often than the specified time interval.
+ * When that interval is exceeded, it logs a message at the specified log
+ * level. It uses LL_MUMBLES_ONCE() logic to prevent spamming, since a too-
+ * frequent call may well be spammy.
+ */
+template <LLError::ELevel LOGLEVEL, typename SIGNATURE>
+class LogThrottle: public Throttle<SIGNATURE>
+{
+    using super = Throttle<SIGNATURE>;
+public:
+    LogThrottle(const std::string& desc,
+                const std::function<SIGNATURE>& func,
+                F64 interval):
+        super(desc, func, interval)
+    {}
+    template <typename R, class C>
+    LogThrottle(const std::string& desc, R C::* method, F64 interval):
+        super(desc, method, interval)
+    {}
+    template <typename R, class C>
+    LogThrottle(const std::string& desc, R C::* method, C* instance, F64 interval):
+        super(desc, method, instance, interval)
+    {}
+    template <typename R, class C>
+    LogThrottle(const std::string& desc, R C::* method, const C* instance, F64 interval):
+        super(desc, method, instance, interval)
+    {}
+
+private:
+    void suppress() override
+    {
+        // Using lllog(), the macro underlying LL_WARNS() et al., allows
+        // specifying compile-time LOGLEVEL. It does NOT support a variable
+        // LOGLEVEL, which is why LOGLEVEL is a non-type template parameter.
+        // See llvlog() for variable support, which is a bit more expensive.
+        // true = only print the log message once
+        lllog(LOGLEVEL, true, "LogThrottle") << std::quoted(super::mDesc)
+                                             << " called more than once per "
+                                             << super::mInterval
+                                             << LL_ENDL;
+    }
+};
+
+#endif /* ! defined(LL_THROTTLE_H) */