Override get_rcl_allocator for TLSF allocators.

This removes one more user of the broken generic version of
get_rcl_allocator, which is causing
ros2/rclcpp#1254.

Author: stevewolter

tlsf_cpp/include/tlsf_cpp/tlsf.hpp

@@ -23,13 +23,16 @@
 #include <new>
 #include <stdexcept>
 
+#include "rcl/allocator.h"
+#include "rclcpp/allocator/allocator_common.hpp"
 #include "tlsf/tlsf.h"
 
 template<typename T, size_t DefaultPoolSize = 1024 * 1024>
 struct tlsf_heap_allocator
 {
   // Needed for std::allocator_traits
   using value_type = T;
+  static const bool is_tlsf_heap_allocator = true;
 
   explicit tlsf_heap_allocator(size_t size)
   : memory_pool(nullptr), pool_size(size)
@@ -137,4 +140,24 @@ constexpr bool operator!=(
   return a.memory_pool != b.memory_pool;
 }
 
+template<typename T, size_t PoolSize>
+rcl_allocator_t get_rcl_allocator(tlsf_heap_allocator<T, PoolSize>& allocator)
+{
+  rcl_allocator_t rcl_allocator;
+  rcl_allocator.allocate = [](size_t size, void*) {
+    return tlsf_malloc(size);
+  };
+  rcl_allocator.deallocate = [](void* pointer, void*) {
+    return tlsf_free(pointer);
+  };
+  rcl_allocator.reallocate = [](void* pointer, size_t size, void*) {
+    return tlsf_realloc(pointer, size);
+  };
+  rcl_allocator.zero_allocate = [](size_t nmemb, size_t size, void*) {
+    return tlsf_calloc(nmemb, size);
+  };
+  rcl_allocator.state = &allocator;
+  return rcl_allocator;
+}
+
 #endif  // TLSF_CPP__TLSF_HPP_