Recycle serialization buffers on transmission

Adds a LIFO buffer pool in the context to reuse buffers allocated
on serialization. The aim is not (only) to avoid the overhead of
dynamic allocation but rather to enhance the cache locality of
serialization buffers.

rmw_zenoh_cpp/src/detail/buffer_pool.hpp

@@ -0,0 +1,86 @@
+// Copyright 2024 Open Source Robotics Foundation, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef DETAIL__BUFFER_POOL_HPP_
+#define DETAIL__BUFFER_POOL_HPP_
+
+#include <mutex>
+#include <cassert>
+#include <vector>
+
+#include "rcutils/allocator.h"
+
+class BufferPool
+{
+public:
+  BufferPool() = default;
+
+  uint8_t * allocate(rcutils_allocator_t *allocator, size_t size)
+  {
+    // FIXME(fuzzypixelz): indeed, this methods leaks all allocated buffers ;)
+    std::lock_guard<std::mutex> guard(mutex_);
+
+    if (available_buffers_.empty()) {
+      uint8_t * data = static_cast<uint8_t *>(allocator->allocate(size, allocator->state));
+      if (data == nullptr) {
+        return nullptr;
+      }
+      Buffer buffer;
+      buffer.data = data;
+      buffer.size = size;
+      buffers_.push_back(buffer);
+      return data;
+    } else {
+      size_t available_buffer = available_buffers_.back();
+      Buffer & buffer = buffers_.at(available_buffer);
+      if (buffer.size < size) {
+        uint8_t * data = static_cast<uint8_t *>(allocator->reallocate(
+                    buffer.data, size, allocator->state));
+        if (data == nullptr) {
+          return nullptr;
+        }
+        buffer.data = data;
+        buffer.size = size;
+      }
+      available_buffers_.pop_back();
+      return buffer.data;
+    }
+  }
+
+  void
+  deallocate(uint8_t *data)
+  {
+    std::lock_guard<std::mutex> guard(mutex_);
+
+    for (size_t i = 0; i < buffers_.size(); i++) {
+      if (buffers_.at(i).data == data) {
+        available_buffers_.push_back(i);
+        return;
+      }
+    }
+  }
+
+private:
+  struct Buffer
+  {
+    uint8_t *data;
+    size_t size;
+  };
+
+  std::vector<Buffer> buffers_;
+  std::vector<size_t> available_buffers_;
+  std::mutex mutex_;
+};
+
+#endif  // DETAIL__BUFFER_POOL_HPP_

rmw_zenoh_cpp/src/detail/rmw_context_impl_s.hpp

@@ -24,6 +24,7 @@
 
 #include "graph_cache.hpp"
 #include "rmw_node_data.hpp"
+#include "buffer_pool.hpp"
 
 #include "rmw/ret_types.h"
 #include "rmw/types.h"
@@ -92,6 +93,9 @@ struct rmw_context_impl_s final
   // Forward declaration
   class Data;
 
+  // Pool of serialization buffers.
+  BufferPool serialization_buffer_pool;
+
 private:
   std::shared_ptr<Data> data_{nullptr};
 };

rmw_zenoh_cpp/src/detail/rmw_publisher_data.cpp

@@ -227,6 +227,12 @@ PublisherData::PublisherData(
   events_mgr_ = std::make_shared<EventsManager>();
 }
 
+void delete_z_bytes(void *data, void *context)
+{
+  BufferPool *pool = reinterpret_cast<BufferPool *>(context);
+  pool->deallocate(static_cast<uint8_t *>(data));
+}
+
 ///=============================================================================
 rmw_ret_t PublisherData::publish(
   const void * ros_message,
@@ -244,7 +250,7 @@ rmw_ret_t PublisherData::publish(
     type_support_impl_);
 
   // To store serialized message byte array.
-  char * msg_bytes = nullptr;
+  uint8_t * msg_bytes = nullptr;
   std::optional<z_owned_shm_mut_t> shmbuf = std::nullopt;
   auto always_free_shmbuf = rcpputils::make_scope_exit(
     [&shmbuf]() {
@@ -254,13 +260,7 @@ rmw_ret_t PublisherData::publish(
     });
 
   rcutils_allocator_t * allocator = &rmw_node_->context->options.allocator;
-
-  auto always_free_msg_bytes = rcpputils::make_scope_exit(
-    [&msg_bytes, allocator, &shmbuf]() {
-      if (msg_bytes && !shmbuf.has_value()) {
-        allocator->deallocate(msg_bytes, allocator->state);
-      }
-    });
+  rmw_context_impl_s * context_impl = static_cast<rmw_context_impl_s *>(rmw_node_->data);
 
   // Get memory from SHM buffer if available.
   if (shm_provider.has_value()) {
@@ -274,21 +274,21 @@ rmw_ret_t PublisherData::publish(
 
     if (alloc.status == ZC_BUF_LAYOUT_ALLOC_STATUS_OK) {
       shmbuf = std::make_optional(alloc.buf);
-      msg_bytes = reinterpret_cast<char *>(z_shm_mut_data_mut(z_loan_mut(alloc.buf)));
+      msg_bytes = reinterpret_cast<uint8_t *>(z_shm_mut_data_mut(z_loan_mut(alloc.buf)));
     } else {
       // TODO(Yadunund): Should we revert to regular allocation and not return an error?
       RMW_SET_ERROR_MSG("Failed to allocate a SHM buffer, even after GCing.");
       return RMW_RET_ERROR;
     }
   } else {
-    // Get memory from the allocator.
-    msg_bytes = static_cast<char *>(allocator->allocate(max_data_length, allocator->state));
+    // Get memory from the buffer pool.
+    msg_bytes = context_impl->serialization_buffer_pool.allocate(allocator, max_data_length);
     RMW_CHECK_FOR_NULL_WITH_MSG(
       msg_bytes, "bytes for message is null", return RMW_RET_BAD_ALLOC);
   }
 
   // Object that manages the raw buffer
-  eprosima::fastcdr::FastBuffer fastbuffer(msg_bytes, max_data_length);
+  eprosima::fastcdr::FastBuffer fastbuffer(reinterpret_cast<char *>(msg_bytes), max_data_length);
 
   // Object that serializes the data
   rmw_zenoh_cpp::Cdr ser(fastbuffer);
@@ -318,7 +318,8 @@ rmw_ret_t PublisherData::publish(
   if (shmbuf.has_value()) {
     z_bytes_from_shm_mut(&payload, z_move(shmbuf.value()));
   } else {
-    z_bytes_copy_from_buf(&payload, reinterpret_cast<const uint8_t *>(msg_bytes), data_length);
+    z_bytes_from_buf(&payload, msg_bytes, data_length, delete_z_bytes,
+        reinterpret_cast<void *>(&context_impl->serialization_buffer_pool));
   }
 
   z_result_t res = z_publisher_put(z_loan(pub_), z_move(payload), &options);