Add LLIntTracker<T>, an LLInstanceTracker<T, int> with generated keys.

The point of LLIntTracker is to generate its keys implicitly, so that its int
getKey() can be treated more or less like an instance pointer, with the added
bonus that the key can be passed around via LLSD.

LLIntTracker generates random int keys to try to make it a little harder for
one script to mess with an LLIntTracker instance belonging to another.

2 files changed, 44 insertions, 0 deletions

diff --git a/indra/llcommon/CMakeLists.txt b/indra/llcommon/CMakeLists.txt
index 8472eac9f6..8577d94be1 100644
--- a/indra/llcommon/CMakeLists.txt
+++ b/indra/llcommon/CMakeLists.txt
@@ -189,6 +189,7 @@ set(llcommon_HEADER_FILES
     llinitparam.h
     llinstancetracker.h
     llinstancetrackersubclass.h
+    llinttracker.h
     llkeybind.h
     llkeythrottle.h
     llleap.h
diff --git a/indra/llcommon/llinttracker.h b/indra/llcommon/llinttracker.h
new file mode 100644
index 0000000000..86c30bc7aa
--- /dev/null
+++ b/indra/llcommon/llinttracker.h
@@ -0,0 +1,43 @@
+/**
+ * @file   llinttracker.h
+ * @author Nat Goodspeed
+ * @date   2024-08-30
+ * @brief  LLIntTracker isa LLInstanceTracker with generated int keys.
+ * 
+ * $LicenseInfo:firstyear=2024&license=viewerlgpl$
+ * Copyright (c) 2024, Linden Research, Inc.
+ * $/LicenseInfo$
+ */
+
+#if ! defined(LL_LLINTTRACKER_H)
+#define LL_LLINTTRACKER_H
+
+#include "llinstancetracker.h"
+
+template <typename T>
+class LLIntTracker: public LLInstanceTracker<T, int>
+{
+    using super = LLInstanceTracker<T, int>;
+public:
+    LLIntTracker():
+        super(getUniqueKey())
+    {}
+
+private:
+    static int getUniqueKey()
+    {
+        // Find a random key that does NOT already correspond to an instance.
+        // Passing a duplicate key to LLInstanceTracker would do Bad Things.
+        int key;
+        do
+        {
+            key = std::rand();
+        } while (super::getInstance(key));
+        // This could be racy, if we were instantiating new LLIntTracker<T>s
+        // on multiple threads. If we need that, have to lock between checking
+        // getInstance() and constructing the new super.
+        return key;
+    }
+};
+
+#endif /* ! defined(LL_LLINTTRACKER_H) */