Recycle serialization buffers on transmission

Adds a bounded 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 +1,121 @@
+// 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 <cstddef>
+#include <cstdlib>
+#include <mutex>
+#include <vector>
+
+#include "rcutils/allocator.h"
+#include "rcutils/env.h"
+#include "logging_macros.hpp"
+
+class BufferPool
+{
+public:
+  struct Buffer
+  {
+    uint8_t * data;
+    size_t size;
+  };
+
+  BufferPool()
+  : buffers_(), mutex_()
+  {
+    const char * env_value;
+    const char * error_str = rcutils_get_env("RMW_ZENOH_BUFFER_POOL_MAX_SIZE_BYTES", &env_value);
+    if (error_str != nullptr) {
+      RMW_ZENOH_LOG_ERROR_NAMED(
+        "rmw_zenoh_cpp",
+        "Unable to read maximum buffer pool size, falling back to default.");
+      max_size_ = DEFAULT_MAX_SIZE;
+    } else {
+      max_size_ = std::atoll(env_value);
+    }
+    size_ = 0;
+  }
+
+  ~BufferPool()
+  {
+    rcutils_allocator_t allocator = rcutils_get_default_allocator();
+
+    for (Buffer & buffer : buffers_) {
+      allocator.deallocate(buffer.data, allocator.state);
+    }
+  }
+
+  Buffer allocate(size_t size)
+  {
+    std::lock_guard<std::mutex> guard(mutex_);
+
+    rcutils_allocator_t allocator = rcutils_get_default_allocator();
+
+    if (buffers_.empty()) {
+      if (size_ + size > max_size_) {
+        return {};
+      } else {
+        size_ += size;
+      }
+      uint8_t * data = static_cast<uint8_t *>(allocator.allocate(size, allocator.state));
+      if (data == nullptr) {
+        return {};
+      } else {
+        return Buffer {data, size};
+      }
+    } else {
+      Buffer buffer = buffers_.back();
+      buffers_.pop_back();
+      if (buffer.size < size) {
+        size_t size_diff = size - buffer.size;
+        if (size_ + size_diff > max_size_) {
+          return {};
+        } else {
+          size_ += size_diff;
+        }
+        uint8_t * data = static_cast<uint8_t *>(allocator.reallocate(
+            buffer.data, size, allocator.state));
+        if (data == nullptr) {
+          return {};
+        } else {
+          buffer.data = data;
+          buffer.size = size;
+        }
+      }
+      return buffer;
+    }
+  }
+
+  void
+  deallocate(Buffer buffer)
+  {
+    std::lock_guard<std::mutex> guard(mutex_);
+    buffers_.push_back(buffer);
+  }
+
+private:
+  std::vector<Buffer> buffers_;
+  std::mutex mutex_;
+  size_t max_size_;
+  size_t size_;
+  // NOTE(fuzzypixelz): Pooled buffers are recycled with the expectation that they would reside in
+  // cache, thus this this value should be comparable to the size of a modern CPU cache. The default
+  // value (16 MiB) is relatively conservative as CPU cache sizes range from a few MiB to a few
+  // hundred MiB.
+  const size_t DEFAULT_MAX_SIZE = 16 * 1024 * 1024;
+};
+
+#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

@@ -216,24 +216,26 @@ rmw_ret_t PublisherData::publish(
     type_support_impl_);
 
   // To store serialized message byte array.
-  char * msg_bytes = nullptr;
-
-  rcutils_allocator_t * allocator = &rmw_node_->context->options.allocator;
-
-  auto always_free_msg_bytes = rcpputils::make_scope_exit(
-    [&msg_bytes, allocator]() {
-      if (msg_bytes) {
-        allocator->deallocate(msg_bytes, allocator->state);
-      }
-    });
-
-  // Get memory from the allocator.
-  msg_bytes = static_cast<char *>(allocator->allocate(max_data_length, allocator->state));
-  RMW_CHECK_FOR_NULL_WITH_MSG(
-    msg_bytes, "bytes for message is null", return RMW_RET_BAD_ALLOC);
+  uint8_t * msg_bytes = nullptr;
+
+  rmw_context_impl_s *context_impl = static_cast<rmw_context_impl_s *>(rmw_node_->data);
+
+  rcutils_allocator_t allocator = rcutils_get_default_allocator();
+
+  // Try to get memory from the serialization buffer pool.
+  BufferPool::Buffer serialization_buffer =
+    context_impl->serialization_buffer_pool.allocate(max_data_length);
+  if (serialization_buffer.data == nullptr) {
+    void * data = allocator.allocate(max_data_length, allocator.state);
+    RMW_CHECK_FOR_NULL_WITH_MSG(
+      msg_bytes, "failed to allocate serialization buffer", return RMW_RET_BAD_ALLOC);
+    msg_bytes = static_cast<uint8_t *>(data);
+  } else {
+    msg_bytes = serialization_buffer.data;
+  }
 
   // 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);
@@ -258,10 +260,19 @@ rmw_ret_t PublisherData::publish(
     sequence_number_++, source_timestamp, entity_->copy_gid()).serialize_to_zbytes();
 
   // TODO(ahcorde): shmbuf
-  std::vector<uint8_t> raw_data(
-    reinterpret_cast<const uint8_t *>(msg_bytes),
-    reinterpret_cast<const uint8_t *>(msg_bytes) + data_length);
-  zenoh::Bytes payload(std::move(raw_data));
+  zenoh::Bytes payload;
+  if (serialization_buffer.data == nullptr) {
+    std::vector<uint8_t> raw_data(
+      reinterpret_cast<const uint8_t *>(msg_bytes),
+      reinterpret_cast<const uint8_t *>(msg_bytes) + data_length);
+    payload = zenoh::Bytes(std::move(raw_data));
+  } else {
+    auto delete_bytes = [buffer_pool = &context_impl->serialization_buffer_pool,
+        buffer = serialization_buffer](uint8_t *){
+        buffer_pool->deallocate(buffer);
+      };
+    payload = zenoh::Bytes(msg_bytes, data_length, delete_bytes);
+  }
 
   TRACETOOLS_TRACEPOINT(
     rmw_publish, static_cast<const void *>(rmw_publisher_), ros_message, source_timestamp);