merge up to 3.6.10-release; some of the storm-68 changes lost

1 files changed, 117 insertions, 0 deletions

diff --git a/indra/llcommon/lltypeinfolookup.h b/indra/llcommon/lltypeinfolookup.h
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+/**
+ * @file   lltypeinfolookup.h
+ * @author Nat Goodspeed
+ * @date   2012-04-08
+ * @brief  Template data structure like std::map<std::type_info*, T>
+ * 
+ * $LicenseInfo:firstyear=2012&license=viewerlgpl$
+ * Copyright (c) 2012, Linden Research, Inc.
+ * $/LicenseInfo$
+ */
+
+#if ! defined(LL_LLTYPEINFOLOOKUP_H)
+#define LL_LLTYPEINFOLOOKUP_H
+
+#include <boost/unordered_map.hpp>
+#include <boost/functional/hash.hpp>
+#include <boost/optional.hpp>
+#include <functional>               // std::binary_function
+#include <typeinfo>
+
+/**
+ * The following helper classes are based on the Boost.Unordered documentation:
+ * http://www.boost.org/doc/libs/1_45_0/doc/html/unordered/hash_equality.html
+ */
+
+/**
+ * Compute hash for a string passed as const char*
+ */
+struct const_char_star_hash: public std::unary_function<const char*, std::size_t>
+{
+    std::size_t operator()(const char* str) const
+    {
+        std::size_t seed = 0;
+        for ( ; *str; ++str)
+        {
+            boost::hash_combine(seed, *str);
+        }
+        return seed;
+    }
+};
+
+/**
+ * Compute equality for strings passed as const char*
+ *
+ * I (nat) suspect that this is where the default behavior breaks for the
+ * const char* values returned from std::type_info::name(). If you compare the
+ * two const char* pointer values, as a naive, unspecialized implementation
+ * will surely do, they'll compare unequal.
+ */
+struct const_char_star_equal: public std::binary_function<const char*, const char*, bool>
+{
+    bool operator()(const char* lhs, const char* rhs) const
+    {
+        return strcmp(lhs, rhs) == 0;
+    }
+};
+
+/**
+ * LLTypeInfoLookup is specifically designed for use cases for which you might
+ * consider std::map<std::type_info*, VALUE>. We have several such data
+ * structures in the viewer. The trouble with them is that at least on Linux,
+ * you can't rely on always getting the same std::type_info* for a given type:
+ * different load modules will produce different std::type_info*.
+ * LLTypeInfoLookup contains a workaround to address this issue.
+ *
+ * The API deliberately diverges from std::map in several respects:
+ * * It avoids iterators, not only begin()/end() but also as return values
+ *   from insert() and find(). This bypasses transform_iterator overhead.
+ * * Since we literally use compile-time types as keys, the essential insert()
+ *   and find() methods accept the key type as a @em template parameter,
+ *   accepting and returning value_type as a normal runtime value. This is to
+ *   permit future optimization (e.g. compile-time type hashing) without
+ *   changing the API.
+ */
+template <typename VALUE>
+class LLTypeInfoLookup
+{
+    // Use this for our underlying implementation: lookup by
+    // std::type_info::name() string. This is one of the rare cases in which I
+    // dare use const char* directly, rather than std::string, because I'm
+    // sure that every value returned by std::type_info::name() is static.
+    // HOWEVER, specify our own hash + equality functors: naively comparing
+    // distinct const char* values won't work.
+    typedef boost::unordered_map<const char*, VALUE,
+                                 const_char_star_hash, const_char_star_equal> impl_map_type;
+
+public:
+    typedef VALUE value_type;
+
+    LLTypeInfoLookup() {}
+
+    bool empty() const { return mMap.empty(); }
+    std::size_t size() const { return mMap.size(); }
+
+    template <typename KEY>
+    bool insert(const value_type& value)
+    {
+        // Obtain and store the std::type_info::name() string as the key.
+        // Return just the bool from std::map::insert()'s return pair.
+        return mMap.insert(typename impl_map_type::value_type(typeid(KEY).name(), value)).second;
+    }
+
+    template <typename KEY>
+    boost::optional<value_type> find() const
+    {
+        // Use the std::type_info::name() string as the key.
+        typename impl_map_type::const_iterator found = mMap.find(typeid(KEY).name());
+        if (found == mMap.end())
+            return boost::optional<value_type>();
+        return found->second;
+    }
+
+private:
+    impl_map_type mMap;
+};
+
+#endif /* ! defined(LL_LLTYPEINFOLOOKUP_H) */