From 6b9b42f314575c15acc564b013b888b0b3672139 Mon Sep 17 00:00:00 2001
From: Artem Pavlenko <artem@mapnik.org>
Date: Thu, 18 Mar 2021 16:05:58 +0000
Subject: [PATCH] Declare `proj_cache_` `thread_local static` to allow
 mapnik::Map to be thread-safe under certain conditions + refactor
 (benchmark/src/test_rendering_shared_map.cpp)

---
 include/mapnik/map.hpp |  3 +-
 src/map.cpp            | 62 +++++++++++++++++++-----------------------
 2 files changed, 30 insertions(+), 35 deletions(-)

diff --git a/include/mapnik/map.hpp b/include/mapnik/map.hpp
index ba1b08b7b..af60147ec 100644
--- a/include/mapnik/map.hpp
+++ b/include/mapnik/map.hpp
@@ -131,7 +131,7 @@ private:
     boost::optional<std::string> font_directory_;
     freetype_engine::font_file_mapping_type font_file_mapping_;
     freetype_engine::font_memory_cache_type font_memory_cache_;
-    mutable proj_cache_type proj_cache_;
+    thread_local static proj_cache_type proj_cache_;
 public:
 
     using const_style_iterator = std::map<std::string,feature_type_style>::const_iterator;
@@ -534,6 +534,7 @@ public:
 private:
     friend void swap(Map & rhs, Map & lhs);
     void fixAspectRatio();
+    void init_proj_transform(std::string const& source, std::string const& dest);
     void init_proj_transforms();
 };
 
diff --git a/src/map.cpp b/src/map.cpp
index 10e281863..5763f1474 100644
--- a/src/map.cpp
+++ b/src/map.cpp
@@ -111,8 +111,7 @@ Map::Map(Map const& rhs)
       font_directory_(rhs.font_directory_),
       font_file_mapping_(rhs.font_file_mapping_),
       // on copy discard memory caches
-      font_memory_cache_(),
-      proj_cache_()
+      font_memory_cache_()
 {
     init_proj_transforms();
 }
@@ -137,11 +136,12 @@ Map::Map(Map && rhs)
       extra_params_(std::move(rhs.extra_params_)),
       font_directory_(std::move(rhs.font_directory_)),
       font_file_mapping_(std::move(rhs.font_file_mapping_)),
-      font_memory_cache_(std::move(rhs.font_memory_cache_)),
-      proj_cache_(std::move(rhs.proj_cache_)) {}
+      font_memory_cache_(std::move(rhs.font_memory_cache_)) {}
 
 Map::~Map() {}
 
+thread_local Map::proj_cache_type Map::proj_cache_ = proj_cache_type();
+
 Map& Map::operator=(Map rhs)
 {
     swap(*this, rhs);
@@ -329,6 +329,7 @@ size_t Map::layer_count() const
 
 proj_transform * Map::get_proj_transform(std::string const& source, std::string const& dest) const
 {
+
     compatible_key_type key = std::make_pair<boost::string_view, boost::string_view>(source, dest);
     auto itr = proj_cache_.find(key, compatible_hash{}, compatible_predicate{});
     if (itr == proj_cache_.end())
@@ -343,29 +344,13 @@ proj_transform * Map::get_proj_transform(std::string const& source, std::string
 
 void Map::add_layer(layer const& l)
 {
-    compatible_key_type key = std::make_pair<boost::string_view, boost::string_view>(srs_, l.srs());
-    auto itr = proj_cache_.find(key, compatible_hash{}, compatible_predicate{});
-    if (itr == proj_cache_.end())
-    {
-        mapnik::projection source(srs_, true);
-        mapnik::projection dest(l.srs(), true);
-        proj_cache_.emplace(std::make_pair(srs_, l.srs()),
-                            std::make_unique<proj_transform>(source, dest));
-    }
+    init_proj_transform(srs_, l.srs());
     layers_.emplace_back(l);
 }
 
 void Map::add_layer(layer && l)
 {
-    compatible_key_type key = std::make_pair<boost::string_view, boost::string_view>(srs_, l.srs());
-    auto itr = proj_cache_.find(key, compatible_hash{}, compatible_predicate{});
-    if (itr == proj_cache_.end())
-    {
-        mapnik::projection source(srs_, true);
-        mapnik::projection dest(l.srs(), true);
-        proj_cache_.emplace(make_pair(srs_, l.srs()),
-                            std::make_unique<proj_transform>(source, dest));
-    }
+    init_proj_transform(srs_, l.srs());
     layers_.push_back(std::move(l));
 }
 
@@ -458,8 +443,9 @@ std::string const&  Map::srs() const
 
 void Map::set_srs(std::string const& _srs)
 {
+    if (srs_ != _srs) init_proj_transforms();
     srs_ = _srs;
-    init_proj_transforms();
+
 }
 
 void Map::set_buffer_size(int _buffer_size)
@@ -808,20 +794,28 @@ void Map::set_extra_parameters(parameters& params)
     extra_params_ = params;
 }
 
-void Map::init_proj_transforms()
+
+void Map::init_proj_transform(std::string const& source, std::string const& dest)
 {
-    for (auto const& l : layers_)
+    compatible_key_type key = std::make_pair<boost::string_view, boost::string_view>(source, dest);
+    auto itr = proj_cache_.find(key, compatible_hash{}, compatible_predicate{});
+    if (itr == proj_cache_.end())
     {
-        compatible_key_type key = std::make_pair<boost::string_view, boost::string_view>(srs_, l.srs());
-        auto itr = proj_cache_.find(key, compatible_hash{}, compatible_predicate{});
-        if (itr == proj_cache_.end())
-        {
-            mapnik::projection source(srs_, true);
-            mapnik::projection dest(l.srs(), true);
-            proj_cache_.emplace(std::make_pair(srs_, l.srs()),
-                                std::make_unique<proj_transform>(source, dest));
-        }
+        mapnik::projection p0(source, true);
+        mapnik::projection p1(dest, true);
+        proj_cache_.emplace(std::make_pair(source, dest),
+                            std::make_unique<proj_transform>(p0, p1));
     }
 }
 
+void Map::init_proj_transforms()
+{
+    std::for_each(layers_.begin(),
+                  layers_.end(),
+                  [this] (auto const& l)
+                  {
+                      init_proj_transform(srs_, l.srs());
+                  });
+}
+
 }