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diff --git a/indra/llcommon/llleap.h b/indra/llcommon/llleap.h
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+++ b/indra/llcommon/llleap.h
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+/**
+ * @file   llleap.h
+ * @author Nat Goodspeed
+ * @date   2012-02-20
+ * @brief  Class that implements "LLSD Event API Plugin"
+ * 
+ * $LicenseInfo:firstyear=2012&license=viewerlgpl$
+ * Copyright (c) 2012, Linden Research, Inc.
+ * $/LicenseInfo$
+ */
+
+#if ! defined(LL_LLLEAP_H)
+#define LL_LLLEAP_H
+
+#include "llinstancetracker.h"
+#include <string>
+#include <vector>
+#include <stdexcept>
+
+/**
+ * LLSD Event API Plugin class. Because instances are managed by
+ * LLInstanceTracker, you can instantiate LLLeap and forget the instance
+ * unless you need it later. Each instance manages an LLProcess; when the
+ * child process terminates, LLLeap deletes itself. We don't require a unique
+ * LLInstanceTracker key.
+ *
+ * The fact that a given LLLeap instance vanishes when its child process
+ * terminates makes it problematic to store an LLLeap* anywhere. Any stored
+ * LLLeap* pointer should be validated before use by
+ * LLLeap::getInstance(LLLeap*) (see LLInstanceTracker).
+ */
+class LL_COMMON_API LLLeap: public LLInstanceTracker<LLLeap>
+{
+public:
+    /**
+     * Pass a brief string description, mostly for logging purposes. The desc
+     * need not be unique, but obviously the clearer we can make it, the
+     * easier these things will be to debug. The strings are the command line
+     * used to launch the desired plugin process.
+     *
+     * Pass exc=false to suppress LLLeap::Error exception. Obviously in that
+     * case the caller cannot discover the nature of the error, merely that an
+     * error of some kind occurred (because create() returned NULL). Either
+     * way, the error is logged.
+     */
+    static LLLeap* create(const std::string& desc, const std::vector<std::string>& plugin,
+                          bool exc=true);
+
+    /**
+     * Pass a brief string description, mostly for logging purposes. The desc
+     * need not be unique, but obviously the clearer we can make it, the
+     * easier these things will be to debug. Pass a command-line string
+     * to launch the desired plugin process.
+     *
+     * Pass exc=false to suppress LLLeap::Error exception. Obviously in that
+     * case the caller cannot discover the nature of the error, merely that an
+     * error of some kind occurred (because create() returned NULL). Either
+     * way, the error is logged.
+     */
+    static LLLeap* create(const std::string& desc, const std::string& plugin,
+                          bool exc=true);
+
+    /**
+     * Exception thrown for invalid create() arguments, e.g. no plugin
+     * program. This is more resiliant than an LL_ERRS failure, because the
+     * string(s) passed to create() might come from an external source. This
+     * way the caller can catch LLLeap::Error and try to recover.
+     */
+    struct Error: public std::runtime_error
+    {
+        Error(const std::string& what): std::runtime_error(what) {}
+    };
+
+    virtual ~LLLeap();
+
+protected:
+    LLLeap();
+};
+
+#endif /* ! defined(LL_LLLEAP_H) */