fix: Use default rcl allocator if allocator is std::allocator (backport #3069)

rclcpp/include/rclcpp/message_memory_strategy.hpp

@@ -18,6 +18,7 @@
 #include <memory>
 #include <stdexcept>
 
+#include "rcl/allocator.h"
 #include "rcl/types.h"
 
 #include "rclcpp/allocator/allocator_common.hpp"
@@ -61,15 +62,25 @@ class MessageMemoryStrategy
     message_allocator_ = std::make_shared<MessageAlloc>();
     serialized_message_allocator_ = std::make_shared<SerializedMessageAlloc>();
     buffer_allocator_ = std::make_shared<BufferAlloc>();
-    rcutils_allocator_ = allocator::get_rcl_allocator<char, BufferAlloc>(*buffer_allocator_.get());
+    if constexpr (std::is_same_v<Alloc, std::allocator<void>>) {
+      rcutils_allocator_ = rcl_get_default_allocator();
+    } else {
+      rcutils_allocator_ = allocator::get_rcl_allocator<char,
+          BufferAlloc>(*buffer_allocator_.get());
+    }
   }
 
   explicit MessageMemoryStrategy(std::shared_ptr<Alloc> allocator)
   {
     message_allocator_ = std::make_shared<MessageAlloc>(*allocator.get());
     serialized_message_allocator_ = std::make_shared<SerializedMessageAlloc>(*allocator.get());
     buffer_allocator_ = std::make_shared<BufferAlloc>(*allocator.get());
-    rcutils_allocator_ = allocator::get_rcl_allocator<char, BufferAlloc>(*buffer_allocator_.get());
+    if constexpr (std::is_same_v<Alloc, std::allocator<void>>) {
+      rcutils_allocator_ = rcl_get_default_allocator();
+    } else {
+      rcutils_allocator_ = allocator::get_rcl_allocator<char,
+          BufferAlloc>(*buffer_allocator_.get());
+    }
   }
 
   virtual ~MessageMemoryStrategy() = default;

rclcpp/include/rclcpp/publisher_options.hpp

@@ -119,6 +119,10 @@ struct PublisherOptionsWithAllocator : public PublisherOptionsBase
   rcl_allocator_t
   get_rcl_allocator() const
   {
+    if constexpr (std::is_same_v<Allocator, std::allocator<void>>) {
+      return rcl_get_default_allocator();
+    }
+
     if (!plain_allocator_storage_) {
       plain_allocator_storage_ =
         std::make_shared<PlainAllocator>(*this->get_allocator());

rclcpp/include/rclcpp/strategies/allocator_memory_strategy.hpp

@@ -424,7 +424,11 @@ class AllocatorMemoryStrategy : public memory_strategy::MemoryStrategy
 
   rcl_allocator_t get_allocator() override
   {
-    return rclcpp::allocator::get_rcl_allocator<void *, VoidAlloc>(*allocator_.get());
+    if constexpr (std::is_same_v<Alloc, std::allocator<void>>) {
+      return rcl_get_default_allocator();
+    } else {
+      return rclcpp::allocator::get_rcl_allocator<void *, VoidAlloc>(*allocator_.get());
+    }
   }
 
   size_t number_of_ready_subscriptions() const override

rclcpp/include/rclcpp/subscription_options.hpp

@@ -163,11 +163,15 @@ struct SubscriptionOptionsWithAllocator : public SubscriptionOptionsBase
   rcl_allocator_t
   get_rcl_allocator() const
   {
-    if (!plain_allocator_storage_) {
-      plain_allocator_storage_ =
-        std::make_shared<PlainAllocator>(*this->get_allocator());
+    if constexpr (std::is_same_v<Allocator, std::allocator<void>>) {
+      return rcl_get_default_allocator();
+    } else {
+      if (!plain_allocator_storage_) {
+        plain_allocator_storage_ =
+          std::make_shared<PlainAllocator>(*this->get_allocator());
+      }
+      return rclcpp::allocator::get_rcl_allocator<char>(*plain_allocator_storage_);
     }
-    return rclcpp::allocator::get_rcl_allocator<char>(*plain_allocator_storage_);
   }
 
   // This is a temporal workaround, to make sure that get_allocator()