slop remove alloc in hot path

server/CMakeLists.txt

@@ -63,6 +63,13 @@ if (CORO_HTTP_SERVER_BUILD_TESTS)
     )
     add_test(NAME http_parser_test COMMAND http_parser_test)
 
+    add_executable(stack_future_test tests/stack_future_test.cpp)
+    target_link_libraries(stack_future_test PRIVATE coro_http_server::coro_http_server)
+    set_target_properties(stack_future_test PROPERTIES
+      RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/tests
+    )
+    add_test(NAME stack_future_test COMMAND stack_future_test)
+
     add_executable(http_integration_test tests/http_integration_test.cpp)
     target_link_libraries(http_integration_test PRIVATE coro_http_server::coro_http_server Threads::Threads)
     set_target_properties(http_integration_test PROPERTIES

server/include/http_parser.h

@@ -1,5 +1,5 @@
 #pragma once
-#include "co_future.h"
+#include "non_owning_co_future.h"
 #include "read_iterator.h"
 #include "request_data.h"
 #include <optional>
@@ -81,7 +81,7 @@ class HttpRequestParser {
 
 public:
   HttpRequestParser(IOUring &ring, int fd);
-  CoFuture<RequestReadStatus> ReadRequest(RequestData &request);
+  NonOwningCoFuture<RequestReadStatus> ReadRequest(RequestData &request);
   void MarkContinueSent();
 };
 

server/include/io_uring.h

@@ -1,5 +1,5 @@
 #pragma once
-#include "co_future.h"
+#include "owning_co_future.h"
 #include <array>
 #include <atomic>
 #include <cstddef>
@@ -48,12 +48,12 @@ class IOUring {
   IOUring();
   IOUring &operator=(IOUring &&rhs);
   void Read(int fileDescriptor, std::array<char, kReadBufferSize> &buffer, std::function<void(int)> complete);
-  CoFuture<int> ReadAsync(int fileDescriptor, std::array<char, kReadBufferSize> &buffer);
+  OwningCoFuture<int> ReadAsync(int fileDescriptor, std::array<char, kReadBufferSize> &buffer);
   void Write(int fileDescriptor, std::string_view data, size_t offset, size_t len,
              std::function<void(int)> complete);
-  CoFuture<int> WriteAsync(int fileDescriptor, std::string_view data, size_t offset,
+  OwningCoFuture<int> WriteAsync(int fileDescriptor, std::string_view data, size_t offset,
                               size_t len);
   void Accept(int fileDescriptor, std::function<void(int)> complete);
-  CoFuture<int> AcceptAsync(int fileDescriptor);
+  OwningCoFuture<int> AcceptAsync(int fileDescriptor);
 };
 }

server/include/non_owning_co_future.h

@@ -0,0 +1,316 @@
+#pragma once
+
+#include "owning_co_future.h"
+#include <coroutine>
+#include <exception>
+#include <functional>
+#include <mutex>
+#include <stdexcept>
+#include <type_traits>
+#include <utility>
+
+namespace HTTP {
+
+template <typename T>
+class NonOwningCoFuture;
+
+template <typename T>
+class NonOwningCoFutureCoroutinePromise {
+  using ControlBlock = detail::StackFutureControl<T>;
+
+  ControlBlock control_;
+  std::unique_lock<std::mutex> producerLock_{control_.mutex};
+  bool completed_{false};
+
+  template <typename>
+  friend class NonOwningCoFuture;
+
+  template <typename Fn>
+  void StoreCompletion(Fn &&store) {
+    if (completed_) {
+      throw std::runtime_error("Future already satisfied");
+    }
+    std::forward<Fn>(store)();
+    completed_ = true;
+  }
+
+  void PublishCompletion() noexcept {
+    if (!completed_) {
+      StoreCompletion([this] {
+        control_.exception =
+            std::make_exception_ptr(std::runtime_error("Coroutine did not complete"));
+      });
+    }
+
+    control_.ready.store(true, std::memory_order_release);
+    auto continuation =
+        control_.continuation.exchange(nullptr, std::memory_order_acq_rel);
+    producerLock_.unlock();
+
+    if (continuation) {
+      (*continuation)();
+    }
+  }
+
+public:
+  NonOwningCoFuture<T> get_return_object() {
+    return NonOwningCoFuture<T>(
+        std::coroutine_handle<NonOwningCoFutureCoroutinePromise>::from_promise(
+            *this));
+  }
+
+  std::suspend_never initial_suspend() noexcept { return {}; }
+
+  struct FinalAwaiter {
+    bool await_ready() noexcept { return false; }
+    void await_resume() noexcept {}
+    void await_suspend(
+        std::coroutine_handle<NonOwningCoFutureCoroutinePromise> handle) noexcept {
+      handle.promise().PublishCompletion();
+    }
+  };
+
+  FinalAwaiter final_suspend() noexcept { return {}; }
+
+  template <typename U>
+  requires(!std::is_void_v<T>)
+  void return_value(U &&value) {
+    StoreCompletion([this, value = std::forward<U>(value)]() mutable {
+      control_.value = std::move(value);
+    });
+  }
+
+  void unhandled_exception() {
+    StoreCompletion([this] { control_.exception = std::current_exception(); });
+  }
+};
+
+template <>
+class NonOwningCoFutureCoroutinePromise<void> {
+  using ControlBlock = detail::StackFutureControl<void>;
+
+  ControlBlock control_;
+  std::unique_lock<std::mutex> producerLock_{control_.mutex};
+  bool completed_{false};
+
+  template <typename>
+  friend class NonOwningCoFuture;
+
+  template <typename Fn>
+  void StoreCompletion(Fn &&store) {
+    if (completed_) {
+      throw std::runtime_error("Future already satisfied");
+    }
+    std::forward<Fn>(store)();
+    completed_ = true;
+  }
+
+  void PublishCompletion() noexcept {
+    if (!completed_) {
+      StoreCompletion([this] {
+        control_.exception =
+            std::make_exception_ptr(std::runtime_error("Coroutine did not complete"));
+      });
+    }
+
+    control_.ready.store(true, std::memory_order_release);
+    auto continuation =
+        control_.continuation.exchange(nullptr, std::memory_order_acq_rel);
+    producerLock_.unlock();
+
+    if (continuation) {
+      (*continuation)();
+    }
+  }
+
+public:
+  NonOwningCoFuture<void> get_return_object();
+
+  std::suspend_never initial_suspend() noexcept { return {}; }
+
+  struct FinalAwaiter {
+    bool await_ready() noexcept { return false; }
+    void await_resume() noexcept {}
+    void await_suspend(
+        std::coroutine_handle<NonOwningCoFutureCoroutinePromise> handle) noexcept {
+      handle.promise().PublishCompletion();
+    }
+  };
+
+  FinalAwaiter final_suspend() noexcept { return {}; }
+
+  void return_void() { StoreCompletion([this] { control_.value = true; }); }
+
+  void unhandled_exception() {
+    StoreCompletion([this] { control_.exception = std::current_exception(); });
+  }
+};
+
+template <typename T>
+class NonOwningCoFuture {
+  using Promise = NonOwningCoFutureCoroutinePromise<T>;
+  using Handle = std::coroutine_handle<Promise>;
+  using ControlBlock = typename Promise::ControlBlock;
+
+  Handle handle_{};
+
+  explicit NonOwningCoFuture(Handle handle) : handle_(handle) {}
+
+  template <typename>
+  friend class NonOwningCoFutureCoroutinePromise;
+
+  Promise *promise() const {
+    if (!handle_) {
+      throw std::logic_error("Invalid future");
+    }
+    return &handle_.promise();
+  }
+
+public:
+  NonOwningCoFuture() = default;
+  NonOwningCoFuture(const NonOwningCoFuture &) = delete;
+  NonOwningCoFuture &operator=(const NonOwningCoFuture &) = delete;
+
+  NonOwningCoFuture(NonOwningCoFuture &&rhs) noexcept
+      : handle_(std::exchange(rhs.handle_, {})) {}
+
+  NonOwningCoFuture &operator=(NonOwningCoFuture &&rhs) noexcept {
+    if (this != &rhs) {
+      if (handle_) {
+        handle_.destroy();
+      }
+      handle_ = std::exchange(rhs.handle_, {});
+    }
+    return *this;
+  }
+
+  ~NonOwningCoFuture() {
+    if (handle_) {
+      handle_.destroy();
+    }
+  }
+
+  bool valid() const noexcept { return static_cast<bool>(handle_); }
+
+  bool isReady() const noexcept {
+    if (!handle_) {
+      return false;
+    }
+    return handle_.promise().control_.ready.load(std::memory_order_acquire);
+  }
+
+  T get() {
+    Promise *p = promise();
+    ControlBlock &control = p->control_;
+    if (!control.ready.load(std::memory_order_acquire)) {
+      control.mutex.lock();
+      control.mutex.unlock();
+    }
+
+    if (control.exception) {
+      std::rethrow_exception(control.exception);
+    }
+    if constexpr (!std::is_void_v<T>) {
+      if (!control.value) {
+        throw std::runtime_error("Future has no value");
+      }
+      return *control.value;
+    }
+  }
+
+  T Get() { return get(); }
+
+  bool await_ready() const noexcept { return isReady(); }
+
+  bool await_suspend(std::coroutine_handle<> awaiting) {
+    ControlBlock &control = promise()->control_;
+    auto callback = std::make_shared<typename ControlBlock::Callback>(
+        [awaiting]() mutable {
+          if (awaiting && !awaiting.done()) {
+            awaiting.resume();
+          }
+        });
+
+    if (control.ready.load(std::memory_order_acquire)) {
+      return false;
+    }
+
+    std::shared_ptr<typename ControlBlock::Callback> expected = nullptr;
+    if (!control.continuation.compare_exchange_strong(
+            expected, callback, std::memory_order_acq_rel,
+            std::memory_order_acquire)) {
+      throw std::runtime_error("Tried to set the subscriber second time");
+    }
+
+    if (control.ready.load(std::memory_order_acquire)) {
+      expected = callback;
+      if (control.continuation.compare_exchange_strong(
+              expected, nullptr, std::memory_order_acq_rel,
+              std::memory_order_acquire)) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  T await_resume() { return get(); }
+
+  template <typename T1, typename U = T,
+            typename = std::enable_if_t<!std::is_void_v<U>>>
+  OwningCoFuture<T1> Then(std::function<T1(U)> &&then) {
+    return OwningCoFuture<T1>(
+        [this, thenFn = std::move(then)](OwningCoFuture<T1> &next) mutable {
+          ControlBlock &control = promise()->control_;
+          auto run = [this, &next, thenFn = std::move(thenFn)]() mutable {
+            try {
+              if constexpr (std::is_void_v<T1>) {
+                thenFn(get());
+                next.Set();
+              } else {
+                next.Set(thenFn(get()));
+              }
+            } catch (...) {
+              next.SetException(std::current_exception());
+            }
+          };
+          detail::RegisterContinuation(control, std::move(run));
+        });
+  }
+
+  template <typename T1, typename U = T,
+            typename = std::enable_if_t<std::is_void_v<U>>, typename = void>
+  OwningCoFuture<T1> Then(std::function<T1()> &&then) {
+    return OwningCoFuture<T1>(
+        [this, thenFn = std::move(then)](OwningCoFuture<T1> &next) mutable {
+          ControlBlock &control = promise()->control_;
+          auto run = [this, &next, thenFn = std::move(thenFn)]() mutable {
+            try {
+              get();
+              if constexpr (std::is_void_v<T1>) {
+                thenFn();
+                next.Set();
+              } else {
+                next.Set(thenFn());
+              }
+            } catch (...) {
+              next.SetException(std::current_exception());
+            }
+          };
+          detail::RegisterContinuation(control, std::move(run));
+        });
+  }
+};
+
+inline NonOwningCoFuture<void>
+NonOwningCoFutureCoroutinePromise<void>::get_return_object() {
+  return NonOwningCoFuture<void>(
+      std::coroutine_handle<NonOwningCoFutureCoroutinePromise>::from_promise(
+          *this));
+}
+
+} // namespace HTTP
+
+template <typename T, typename... Args>
+struct std::coroutine_traits<HTTP::NonOwningCoFuture<T>, Args...> {
+  using promise_type = HTTP::NonOwningCoFutureCoroutinePromise<T>;
+};