Initial Commit

include/asio/detail/impl/io_uring_service.ipp

@@ -0,0 +1,918 @@
+//
+// detail/impl/io_uring_service.ipp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_DETAIL_IMPL_IO_URING_SERVICE_IPP
+#define ASIO_DETAIL_IMPL_IO_URING_SERVICE_IPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+
+#if defined(ASIO_HAS_IO_URING)
+
+#include <cstddef>
+#include <sys/eventfd.h>
+#include "asio/detail/io_uring_service.hpp"
+#include "asio/detail/reactor_op.hpp"
+#include "asio/detail/scheduler.hpp"
+#include "asio/detail/throw_error.hpp"
+#include "asio/error.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+io_uring_service::io_uring_service(asio::execution_context& ctx)
+  : execution_context_service_base<io_uring_service>(ctx),
+    scheduler_(use_service<scheduler>(ctx)),
+    mutex_(config(ctx).get("reactor", "registration_locking", true),
+        config(ctx).get("reactor", "registration_locking_spin_count", 0)),
+    outstanding_work_(0),
+    submit_sqes_op_(this),
+    pending_sqes_(0),
+    pending_submit_sqes_op_(false),
+    shutdown_(false),
+    io_locking_(config(ctx).get("reactor", "io_locking", true)),
+    io_locking_spin_count_(
+        config(ctx).get("reactor", "io_locking_spin_count", 0)),
+    timeout_(),
+    registration_mutex_(mutex_.enabled()),
+    registered_io_objects_(execution_context::allocator<void>(ctx),
+        config(ctx).get("reactor", "preallocated_io_objects", 0U),
+        io_locking_, io_locking_spin_count_),
+    reactor_(use_service<reactor>(ctx)),
+    reactor_data_(),
+    event_fd_(-1)
+{
+  reactor_.init_task();
+  init_ring();
+  register_with_reactor();
+}
+
+io_uring_service::~io_uring_service()
+{
+  if (ring_.ring_fd != -1)
+    ::io_uring_queue_exit(&ring_);
+  if (event_fd_ != -1)
+    ::close(event_fd_);
+}
+
+void io_uring_service::shutdown()
+{
+  mutex::scoped_lock lock(mutex_);
+  shutdown_ = true;
+  lock.unlock();
+
+  op_queue<operation> ops;
+
+  // Cancel all outstanding operations.
+  while (io_object* io_obj = registered_io_objects_.first())
+  {
+    for (int i = 0; i < max_ops; ++i)
+    {
+      if (!io_obj->queues_[i].op_queue_.empty())
+      {
+        ops.push(io_obj->queues_[i].op_queue_);
+        if (::io_uring_sqe* sqe = get_sqe())
+          ::io_uring_prep_cancel(sqe, &io_obj->queues_[i], 0);
+      }
+    }
+    io_obj->shutdown_ = true;
+    registered_io_objects_.free(io_obj);
+  }
+
+  // Cancel the timeout operation.
+  if (::io_uring_sqe* sqe = get_sqe())
+    ::io_uring_prep_cancel(sqe, &timeout_, IOSQE_IO_DRAIN);
+  submit_sqes();
+
+  // Wait for all completions to come back.
+  for (; outstanding_work_ > 0; --outstanding_work_)
+  {
+    ::io_uring_cqe* cqe = 0;
+    if (::io_uring_wait_cqe(&ring_, &cqe) != 0)
+      break;
+  }
+
+  timer_queues_.get_all_timers(ops);
+
+  scheduler_.abandon_operations(ops);
+}
+
+void io_uring_service::notify_fork(
+    asio::execution_context::fork_event fork_ev)
+{
+  switch (fork_ev)
+  {
+  case asio::execution_context::fork_prepare:
+    {
+      // Cancel all outstanding operations. They will be restarted
+      // after the fork completes.
+      mutex::scoped_lock registration_lock(registration_mutex_);
+      for (io_object* io_obj = registered_io_objects_.first();
+          io_obj != 0; io_obj = io_obj->next_)
+      {
+        mutex::scoped_lock io_object_lock(io_obj->mutex_);
+        for (int i = 0; i < max_ops; ++i)
+        {
+          if (!io_obj->queues_[i].op_queue_.empty()
+              && !io_obj->queues_[i].cancel_requested_)
+          {
+            mutex::scoped_lock lock(mutex_);
+            if (::io_uring_sqe* sqe = get_sqe())
+              ::io_uring_prep_cancel(sqe, &io_obj->queues_[i], 0);
+          }
+        }
+      }
+
+      // Cancel the timeout operation.
+      {
+        mutex::scoped_lock lock(mutex_);
+        if (::io_uring_sqe* sqe = get_sqe())
+          ::io_uring_prep_cancel(sqe, &timeout_, IOSQE_IO_DRAIN);
+        submit_sqes();
+      }
+
+      // Wait for all completions to come back, and post all completed I/O
+      // queues to the scheduler. Note that some operations may have already
+      // completed, or were explicitly cancelled. All others will be
+      // automatically restarted.
+      op_queue<operation> ops;
+      for (; outstanding_work_ > 0; --outstanding_work_)
+      {
+        ::io_uring_cqe* cqe = 0;
+        if (::io_uring_wait_cqe(&ring_, &cqe) != 0)
+          break;
+        if (void* ptr = ::io_uring_cqe_get_data(cqe))
+        {
+          if (ptr != this && ptr != &timer_queues_ && ptr != &timeout_)
+          {
+            io_queue* io_q = static_cast<io_queue*>(ptr);
+            io_q->set_result(cqe->res);
+            ops.push(io_q);
+          }
+        }
+      }
+      scheduler_.post_deferred_completions(ops);
+
+      // Restart and eventfd operation.
+      register_with_reactor();
+    }
+    break;
+
+  case asio::execution_context::fork_parent:
+    // Restart the timeout and eventfd operations.
+    update_timeout();
+    register_with_reactor();
+    break;
+
+  case asio::execution_context::fork_child:
+    {
+      // The child process gets a new io_uring instance.
+      ::io_uring_queue_exit(&ring_);
+      init_ring();
+      register_with_reactor();
+    }
+    break;
+  default:
+    break;
+  }
+}
+
+void io_uring_service::init_task()
+{
+  scheduler_.init_task();
+}
+
+void io_uring_service::register_io_object(
+    io_uring_service::per_io_object_data& io_obj)
+{
+  io_obj = allocate_io_object();
+
+  mutex::scoped_lock io_object_lock(io_obj->mutex_);
+
+  io_obj->service_ = this;
+  io_obj->shutdown_ = false;
+  for (int i = 0; i < max_ops; ++i)
+  {
+    io_obj->queues_[i].io_object_ = io_obj;
+    io_obj->queues_[i].cancel_requested_ = false;
+  }
+}
+
+void io_uring_service::register_internal_io_object(
+    io_uring_service::per_io_object_data& io_obj,
+    int op_type, io_uring_operation* op)
+{
+  io_obj = allocate_io_object();
+
+  mutex::scoped_lock io_object_lock(io_obj->mutex_);
+
+  io_obj->service_ = this;
+  io_obj->shutdown_ = false;
+  for (int i = 0; i < max_ops; ++i)
+  {
+    io_obj->queues_[i].io_object_ = io_obj;
+    io_obj->queues_[i].cancel_requested_ = false;
+  }
+
+  io_obj->queues_[op_type].op_queue_.push(op);
+  io_object_lock.unlock();
+  mutex::scoped_lock lock(mutex_);
+  if (::io_uring_sqe* sqe = get_sqe())
+  {
+    op->prepare(sqe);
+    ::io_uring_sqe_set_data(sqe, &io_obj->queues_[op_type]);
+    post_submit_sqes_op(lock);
+  }
+  else
+  {
+    asio::error_code ec(ENOBUFS,
+        asio::error::get_system_category());
+    asio::detail::throw_error(ec, "io_uring_get_sqe");
+  }
+}
+
+void io_uring_service::register_buffers(const ::iovec* v, unsigned n)
+{
+  int result = ::io_uring_register_buffers(&ring_, v, n);
+  if (result < 0)
+  {
+    asio::error_code ec(-result,
+        asio::error::get_system_category());
+    asio::detail::throw_error(ec, "io_uring_register_buffers");
+  }
+}
+
+void io_uring_service::unregister_buffers()
+{
+  (void)::io_uring_unregister_buffers(&ring_);
+}
+
+void io_uring_service::start_op(int op_type,
+    io_uring_service::per_io_object_data& io_obj,
+    io_uring_operation* op, bool is_continuation)
+{
+  if (!io_obj)
+  {
+    op->ec_ = asio::error::bad_descriptor;
+    post_immediate_completion(op, is_continuation);
+    return;
+  }
+
+  mutex::scoped_lock io_object_lock(io_obj->mutex_);
+
+  if (io_obj->shutdown_)
+  {
+    io_object_lock.unlock();
+    post_immediate_completion(op, is_continuation);
+    return;
+  }
+
+  if (io_obj->queues_[op_type].op_queue_.empty())
+  {
+    if (op->perform(false))
+    {
+      io_object_lock.unlock();
+      scheduler_.post_immediate_completion(op, is_continuation);
+    }
+    else
+    {
+      io_obj->queues_[op_type].op_queue_.push(op);
+      io_object_lock.unlock();
+      mutex::scoped_lock lock(mutex_);
+      if (::io_uring_sqe* sqe = get_sqe())
+      {
+        op->prepare(sqe);
+        ::io_uring_sqe_set_data(sqe, &io_obj->queues_[op_type]);
+        scheduler_.work_started();
+        post_submit_sqes_op(lock);
+      }
+      else
+      {
+        lock.unlock();
+        io_obj->queues_[op_type].set_result(-ENOBUFS);
+        post_immediate_completion(&io_obj->queues_[op_type], is_continuation);
+      }
+    }
+  }
+  else
+  {
+    io_obj->queues_[op_type].op_queue_.push(op);
+    scheduler_.work_started();
+  }
+}
+
+void io_uring_service::cancel_ops(io_uring_service::per_io_object_data& io_obj)
+{
+  if (!io_obj)
+    return;
+
+  mutex::scoped_lock io_object_lock(io_obj->mutex_);
+  op_queue<operation> ops;
+  do_cancel_ops(io_obj, ops);
+  io_object_lock.unlock();
+  scheduler_.post_deferred_completions(ops);
+}
+
+void io_uring_service::cancel_ops_by_key(
+    io_uring_service::per_io_object_data& io_obj,
+    int op_type, void* cancellation_key)
+{
+  if (!io_obj)
+    return;
+
+  mutex::scoped_lock io_object_lock(io_obj->mutex_);
+
+  bool first = true;
+  op_queue<operation> ops;
+  op_queue<io_uring_operation> other_ops;
+  while (io_uring_operation* op = io_obj->queues_[op_type].op_queue_.front())
+  {
+    io_obj->queues_[op_type].op_queue_.pop();
+    if (op->cancellation_key_ == cancellation_key)
+    {
+      if (first)
+      {
+        other_ops.push(op);
+        if (!io_obj->queues_[op_type].cancel_requested_)
+        {
+          io_obj->queues_[op_type].cancel_requested_ = true;
+          mutex::scoped_lock lock(mutex_);
+          if (::io_uring_sqe* sqe = get_sqe())
+          {
+            ::io_uring_prep_cancel(sqe, &io_obj->queues_[op_type], 0);
+            submit_sqes();
+          }
+        }
+      }
+      else
+      {
+        op->ec_ = asio::error::operation_aborted;
+        ops.push(op);
+      }
+    }
+    else
+      other_ops.push(op);
+    first = false;
+  }
+  io_obj->queues_[op_type].op_queue_.push(other_ops);
+
+  io_object_lock.unlock();
+
+  scheduler_.post_deferred_completions(ops);
+}
+
+void io_uring_service::deregister_io_object(
+    io_uring_service::per_io_object_data& io_obj)
+{
+  if (!io_obj)
+    return;
+
+  mutex::scoped_lock io_object_lock(io_obj->mutex_);
+  if (!io_obj->shutdown_)
+  {
+    op_queue<operation> ops;
+    bool pending_cancelled_ops = do_cancel_ops(io_obj, ops);
+    io_obj->shutdown_ = true;
+    io_object_lock.unlock();
+    scheduler_.post_deferred_completions(ops);
+    if (pending_cancelled_ops)
+    {
+      // There are still pending operations. Prevent cleanup_io_object from
+      // freeing the I/O object and let the last operation to complete free it.
+      io_obj = 0;
+    }
+    else
+    {
+      // Leave io_obj set so that it will be freed by the subsequent call to
+      // cleanup_io_object.
+    }
+  }
+  else
+  {
+    // We are shutting down, so prevent cleanup_io_object from freeing
+    // the I/O object and let the destructor free it instead.
+    io_obj = 0;
+  }
+}
+
+void io_uring_service::cleanup_io_object(
+    io_uring_service::per_io_object_data& io_obj)
+{
+  if (io_obj)
+  {
+    free_io_object(io_obj);
+    io_obj = 0;
+  }
+}
+
+void io_uring_service::run(long usec, op_queue<operation>& ops)
+{
+  __kernel_timespec ts;
+  int local_ops = 0;
+
+  if (usec > 0)
+  {
+    ts.tv_sec = usec / 1000000;
+    ts.tv_nsec = (usec % 1000000) * 1000;
+    mutex::scoped_lock lock(mutex_);
+    if (::io_uring_sqe* sqe = get_sqe())
+    {
+      ++local_ops;
+      ::io_uring_prep_timeout(sqe, &ts, 0, 0);
+      ::io_uring_sqe_set_data(sqe, &ts);
+      submit_sqes();
+    }
+  }
+
+  ::io_uring_cqe* cqe = 0;
+  int result = (usec == 0)
+    ? ::io_uring_peek_cqe(&ring_, &cqe)
+    : ::io_uring_wait_cqe(&ring_, &cqe);
+
+  if (local_ops > 0)
+  {
+    if (result != 0 || ::io_uring_cqe_get_data(cqe) != &ts)
+    {
+      mutex::scoped_lock lock(mutex_);
+      if (::io_uring_sqe* sqe = get_sqe())
+      {
+        ++local_ops;
+        ::io_uring_prep_timeout_remove(sqe, reinterpret_cast<__u64>(&ts), 0);
+        ::io_uring_sqe_set_data(sqe, &ts);
+        submit_sqes();
+      }
+    }
+  }
+
+  bool check_timers = false;
+  int count = 0;
+  while (result == 0 || local_ops > 0)
+  {
+    if (result == 0)
+    {
+      if (void* ptr = ::io_uring_cqe_get_data(cqe))
+      {
+        if (ptr == this)
+        {
+          // The io_uring service was interrupted.
+        }
+        else if (ptr == &timer_queues_)
+        {
+          check_timers = true;
+        }
+        else if (ptr == &timeout_)
+        {
+          check_timers = true;
+          timeout_.tv_sec = 0;
+          timeout_.tv_nsec = 0;
+        }
+        else if (ptr == &ts)
+        {
+          --local_ops;
+        }
+        else
+        {
+          io_queue* io_q = static_cast<io_queue*>(ptr);
+          io_q->set_result(cqe->res);
+          ops.push(io_q);
+        }
+      }
+      ::io_uring_cqe_seen(&ring_, cqe);
+      ++count;
+    }
+    result = (count < complete_batch_size || local_ops > 0)
+      ? ::io_uring_peek_cqe(&ring_, &cqe) : -EAGAIN;
+  }
+
+  decrement(outstanding_work_, count);
+
+  if (check_timers)
+  {
+    mutex::scoped_lock lock(mutex_);
+    timer_queues_.get_ready_timers(ops);
+    if (timeout_.tv_sec == 0 && timeout_.tv_nsec == 0)
+    {
+      timeout_ = get_timeout();
+      if (::io_uring_sqe* sqe = get_sqe())
+      {
+        ::io_uring_prep_timeout(sqe, &timeout_, 0, 0);
+        ::io_uring_sqe_set_data(sqe, &timeout_);
+        push_submit_sqes_op(ops);
+      }
+    }
+  }
+}
+
+void io_uring_service::interrupt()
+{
+  mutex::scoped_lock lock(mutex_);
+  if (::io_uring_sqe* sqe = get_sqe())
+  {
+    ::io_uring_prep_nop(sqe);
+    ::io_uring_sqe_set_data(sqe, this);
+  }
+  submit_sqes();
+}
+
+void io_uring_service::init_ring()
+{
+  int result = ::io_uring_queue_init(ring_size, &ring_, 0);
+  if (result < 0)
+  {
+    ring_.ring_fd = -1;
+    asio::error_code ec(-result,
+        asio::error::get_system_category());
+    asio::detail::throw_error(ec, "io_uring_queue_init");
+  }
+
+#if !defined(ASIO_HAS_IO_URING_AS_DEFAULT)
+  event_fd_ = ::eventfd(0, EFD_CLOEXEC | EFD_NONBLOCK);
+  if (event_fd_ < 0)
+  {
+    asio::error_code ec(-result,
+        asio::error::get_system_category());
+    ::io_uring_queue_exit(&ring_);
+    asio::detail::throw_error(ec, "eventfd");
+  }
+
+  result = ::io_uring_register_eventfd(&ring_, event_fd_);
+  if (result < 0)
+  {
+    ::close(event_fd_);
+    ::io_uring_queue_exit(&ring_);
+    asio::error_code ec(-result,
+        asio::error::get_system_category());
+    asio::detail::throw_error(ec, "io_uring_queue_init");
+  }
+#endif // !defined(ASIO_HAS_IO_URING_AS_DEFAULT)
+}
+
+#if !defined(ASIO_HAS_IO_URING_AS_DEFAULT)
+class io_uring_service::event_fd_read_op :
+  public reactor_op
+{
+public:
+  event_fd_read_op(io_uring_service* s)
+    : reactor_op(asio::error_code(),
+        &event_fd_read_op::do_perform, event_fd_read_op::do_complete),
+      service_(s)
+  {
+  }
+
+  static status do_perform(reactor_op* base)
+  {
+    event_fd_read_op* o(static_cast<event_fd_read_op*>(base));
+
+    for (;;)
+    {
+      // Only perform one read. The kernel maintains an atomic counter.
+      uint64_t counter(0);
+      errno = 0;
+      int bytes_read = ::read(o->service_->event_fd_,
+          &counter, sizeof(uint64_t));
+      if (bytes_read < 0 && errno == EINTR)
+        continue;
+      break;
+    }
+
+    op_queue<operation> ops;
+    o->service_->run(0, ops);
+    o->service_->scheduler_.post_deferred_completions(ops);
+
+    return not_done;
+  }
+
+  static void do_complete(void* /*owner*/, operation* base,
+      const asio::error_code& /*ec*/,
+      std::size_t /*bytes_transferred*/)
+  {
+    event_fd_read_op* o(static_cast<event_fd_read_op*>(base));
+    delete o;
+  }
+
+private:
+  io_uring_service* service_;
+};
+#endif // !defined(ASIO_HAS_IO_URING_AS_DEFAULT)
+
+void io_uring_service::register_with_reactor()
+{
+#if !defined(ASIO_HAS_IO_URING_AS_DEFAULT)
+  reactor_.register_internal_descriptor(reactor::read_op,
+      event_fd_, reactor_data_, new event_fd_read_op(this));
+#endif // !defined(ASIO_HAS_IO_URING_AS_DEFAULT)
+}
+
+io_uring_service::io_object* io_uring_service::allocate_io_object()
+{
+  mutex::scoped_lock registration_lock(registration_mutex_);
+  return registered_io_objects_.alloc(io_locking_, io_locking_spin_count_);
+}
+
+void io_uring_service::free_io_object(io_uring_service::io_object* io_obj)
+{
+  mutex::scoped_lock registration_lock(registration_mutex_);
+  registered_io_objects_.free(io_obj);
+}
+
+bool io_uring_service::do_cancel_ops(
+    per_io_object_data& io_obj, op_queue<operation>& ops)
+{
+  bool cancel_op = false;
+
+  for (int i = 0; i < max_ops; ++i)
+  {
+    if (io_uring_operation* first_op = io_obj->queues_[i].op_queue_.front())
+    {
+      cancel_op = true;
+      io_obj->queues_[i].op_queue_.pop();
+      while (io_uring_operation* op = io_obj->queues_[i].op_queue_.front())
+      {
+        op->ec_ = asio::error::operation_aborted;
+        io_obj->queues_[i].op_queue_.pop();
+        ops.push(op);
+      }
+      io_obj->queues_[i].op_queue_.push(first_op);
+    }
+  }
+
+  if (cancel_op)
+  {
+    mutex::scoped_lock lock(mutex_);
+    for (int i = 0; i < max_ops; ++i)
+    {
+      if (!io_obj->queues_[i].op_queue_.empty()
+          && !io_obj->queues_[i].cancel_requested_)
+      {
+        io_obj->queues_[i].cancel_requested_ = true;
+        if (::io_uring_sqe* sqe = get_sqe())
+          ::io_uring_prep_cancel(sqe, &io_obj->queues_[i], 0);
+      }
+    }
+    submit_sqes();
+  }
+
+  return cancel_op;
+}
+
+void io_uring_service::do_add_timer_queue(timer_queue_base& queue)
+{
+  mutex::scoped_lock lock(mutex_);
+  timer_queues_.insert(&queue);
+}
+
+void io_uring_service::do_remove_timer_queue(timer_queue_base& queue)
+{
+  mutex::scoped_lock lock(mutex_);
+  timer_queues_.erase(&queue);
+}
+
+void io_uring_service::update_timeout()
+{
+  if (::io_uring_sqe* sqe = get_sqe())
+  {
+    ::io_uring_prep_timeout_remove(sqe, reinterpret_cast<__u64>(&timeout_), 0);
+    ::io_uring_sqe_set_data(sqe, &timer_queues_);
+  }
+}
+
+__kernel_timespec io_uring_service::get_timeout() const
+{
+  __kernel_timespec ts;
+  long usec = timer_queues_.wait_duration_usec(5 * 60 * 1000 * 1000);
+  ts.tv_sec = usec / 1000000;
+  ts.tv_nsec = usec ? (usec % 1000000) * 1000 : 1;
+  return ts;
+}
+
+::io_uring_sqe* io_uring_service::get_sqe()
+{
+  ::io_uring_sqe* sqe = ::io_uring_get_sqe(&ring_);
+  if (!sqe)
+  {
+    submit_sqes();
+    sqe = ::io_uring_get_sqe(&ring_);
+  }
+  if (sqe)
+  {
+    ::io_uring_sqe_set_data(sqe, 0);
+    ++pending_sqes_;
+  }
+  return sqe;
+}
+
+void io_uring_service::submit_sqes()
+{
+  if (pending_sqes_ != 0)
+  {
+    int result = ::io_uring_submit(&ring_);
+    if (result > 0)
+    {
+      pending_sqes_ -= result;
+      increment(outstanding_work_, result);
+    }
+  }
+}
+
+void io_uring_service::post_submit_sqes_op(mutex::scoped_lock& lock)
+{
+  if (pending_sqes_ >= submit_batch_size)
+  {
+    submit_sqes();
+  }
+  else if (pending_sqes_ != 0 && !pending_submit_sqes_op_)
+  {
+    pending_submit_sqes_op_ = true;
+    lock.unlock();
+    scheduler_.post_immediate_completion(&submit_sqes_op_, false);
+  }
+}
+
+void io_uring_service::push_submit_sqes_op(op_queue<operation>& ops)
+{
+  if (pending_sqes_ != 0 && !pending_submit_sqes_op_)
+  {
+    pending_submit_sqes_op_ = true;
+    ops.push(&submit_sqes_op_);
+    scheduler_.compensating_work_started();
+  }
+}
+
+io_uring_service::submit_sqes_op::submit_sqes_op(io_uring_service* s)
+  : operation(&io_uring_service::submit_sqes_op::do_complete),
+    service_(s)
+{
+}
+
+void io_uring_service::submit_sqes_op::do_complete(void* owner, operation* base,
+    const asio::error_code& /*ec*/, std::size_t /*bytes_transferred*/)
+{
+  if (owner)
+  {
+    submit_sqes_op* o = static_cast<submit_sqes_op*>(base);
+    mutex::scoped_lock lock(o->service_->mutex_);
+    o->service_->submit_sqes();
+    if (o->service_->pending_sqes_ != 0)
+      o->service_->scheduler_.post_immediate_completion(o, true);
+    else
+      o->service_->pending_submit_sqes_op_ = false;
+  }
+}
+
+io_uring_service::io_queue::io_queue()
+  : operation(&io_uring_service::io_queue::do_complete)
+{
+}
+
+struct io_uring_service::perform_io_cleanup_on_block_exit
+{
+  explicit perform_io_cleanup_on_block_exit(io_uring_service* s)
+    : service_(s), io_object_to_free_(0), first_op_(0)
+  {
+  }
+
+  ~perform_io_cleanup_on_block_exit()
+  {
+    if (io_object_to_free_)
+    {
+      mutex::scoped_lock lock(service_->mutex_);
+      service_->free_io_object(io_object_to_free_);
+    }
+
+    if (first_op_)
+    {
+      // Post the remaining completed operations for invocation.
+      if (!ops_.empty())
+        service_->scheduler_.post_deferred_completions(ops_);
+
+      // A user-initiated operation has completed, but there's no need to
+      // explicitly call work_finished() here. Instead, we'll take advantage of
+      // the fact that the scheduler will call work_finished() once we return.
+    }
+    else
+    {
+      // No user-initiated operations have completed, so we need to compensate
+      // for the work_finished() call that the scheduler will make once this
+      // operation returns.
+      service_->scheduler_.compensating_work_started();
+    }
+  }
+
+  io_uring_service* service_;
+  io_object* io_object_to_free_;
+  op_queue<operation> ops_;
+  operation* first_op_;
+};
+
+operation* io_uring_service::io_queue::perform_io(int result)
+{
+  perform_io_cleanup_on_block_exit io_cleanup(io_object_->service_);
+  mutex::scoped_lock io_object_lock(io_object_->mutex_);
+
+  if (result != -ECANCELED || cancel_requested_)
+  {
+    if (io_uring_operation* op = op_queue_.front())
+    {
+      if (result < 0)
+      {
+        op->ec_.assign(-result, asio::error::get_system_category());
+        op->bytes_transferred_ = 0;
+      }
+      else
+      {
+        op->ec_.assign(0, op->ec_.category());
+        op->bytes_transferred_ = static_cast<std::size_t>(result);
+      }
+    }
+
+    while (io_uring_operation* op = op_queue_.front())
+    {
+      if (op->perform(io_cleanup.ops_.empty()))
+      {
+        op_queue_.pop();
+        io_cleanup.ops_.push(op);
+      }
+      else
+        break;
+    }
+  }
+
+  cancel_requested_ = false;
+
+  if (!op_queue_.empty())
+  {
+    io_uring_service* service = io_object_->service_;
+    mutex::scoped_lock lock(service->mutex_);
+    if (::io_uring_sqe* sqe = service->get_sqe())
+    {
+      op_queue_.front()->prepare(sqe);
+      ::io_uring_sqe_set_data(sqe, this);
+      service->post_submit_sqes_op(lock);
+    }
+    else
+    {
+      lock.unlock();
+      while (io_uring_operation* op = op_queue_.front())
+      {
+        op->ec_ = asio::error::no_buffer_space;
+        op_queue_.pop();
+        io_cleanup.ops_.push(op);
+      }
+    }
+  }
+
+  // The last operation to complete on a shut down object must free it.
+  if (io_object_->shutdown_)
+  {
+    io_cleanup.io_object_to_free_ = io_object_;
+    for (int i = 0; i < max_ops; ++i)
+      if (!io_object_->queues_[i].op_queue_.empty())
+        io_cleanup.io_object_to_free_ = 0;
+  }
+
+  // The first operation will be returned for completion now. The others will
+  // be posted for later by the io_cleanup object's destructor.
+  io_cleanup.first_op_ = io_cleanup.ops_.front();
+  io_cleanup.ops_.pop();
+  return io_cleanup.first_op_;
+}
+
+void io_uring_service::io_queue::do_complete(void* owner, operation* base,
+    const asio::error_code& ec, std::size_t bytes_transferred)
+{
+  if (owner)
+  {
+    io_queue* io_q = static_cast<io_queue*>(base);
+    int result = static_cast<int>(bytes_transferred);
+    if (operation* op = io_q->perform_io(result))
+    {
+      op->complete(owner, ec, 0);
+    }
+  }
+}
+
+io_uring_service::io_object::io_object(bool locking, int spin_count)
+  : mutex_(locking, spin_count)
+{
+}
+
+} // namespace detail
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // defined(ASIO_HAS_IO_URING)
+
+#endif // ASIO_DETAIL_IMPL_IO_URING_SERVICE_IPP