Change CallbackDeferrer to use a variant and callback pointer instead of std::function

This should substantially reduce the overhead due to deferred callbacks in profiles.

Bug: webrtc:15723
Change-Id: I4c52beb91eb08c9b0ac2d1ce9a4e11839aa35e38
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/331020
Reviewed-by: Victor Boivie <boivie@webrtc.org>
Commit-Queue: Daniel Collins <dpcollins@google.com>
Cr-Commit-Position: refs/heads/main@{#41363}

net/dcsctp/socket/BUILD.gn

@@ -178,6 +178,7 @@ rtc_library("dcsctp_socket") {
     "//third_party/abseil-cpp/absl/memory",
     "//third_party/abseil-cpp/absl/strings",
     "//third_party/abseil-cpp/absl/types:optional",
+    "//third_party/abseil-cpp/absl/types:variant",
   ]
 }
 

net/dcsctp/socket/callback_deferrer.cc

@@ -12,31 +12,6 @@
 #include "api/make_ref_counted.h"
 
 namespace dcsctp {
-namespace {
-// A wrapper around the move-only DcSctpMessage, to let it be captured in a
-// lambda.
-class MessageDeliverer {
- public:
-  explicit MessageDeliverer(DcSctpMessage&& message)
-      : state_(rtc::make_ref_counted<State>(std::move(message))) {}
-
-  void Deliver(DcSctpSocketCallbacks& c) {
-    // Really ensure that it's only called once.
-    RTC_DCHECK(!state_->has_delivered);
-    state_->has_delivered = true;
-    c.OnMessageReceived(std::move(state_->message));
-  }
-
- private:
-  struct State : public webrtc::RefCountInterface {
-    explicit State(DcSctpMessage&& m)
-        : has_delivered(false), message(std::move(m)) {}
-    bool has_delivered;
-    DcSctpMessage message;
-  };
-  rtc::scoped_refptr<State> state_;
-};
-}  // namespace
 
 void CallbackDeferrer::Prepare() {
   RTC_DCHECK(!prepared_);
@@ -48,12 +23,12 @@ void CallbackDeferrer::TriggerDeferred() {
   // callback, and that might result in adding new callbacks to this instance,
   // and the vector can't be modified while iterated on.
   RTC_DCHECK(prepared_);
-  std::vector<std::function<void(DcSctpSocketCallbacks & cb)>> deferred;
+  std::vector<std::pair<Callback, CallbackData>> deferred;
   deferred.swap(deferred_);
   prepared_ = false;
 
-  for (auto& cb : deferred) {
-    cb(underlying_);
+  for (auto& [cb, data] : deferred) {
+    cb(std::move(data), underlying_);
   }
 }
 
@@ -84,40 +59,57 @@ uint32_t CallbackDeferrer::GetRandomInt(uint32_t low, uint32_t high) {
 void CallbackDeferrer::OnMessageReceived(DcSctpMessage message) {
   RTC_DCHECK(prepared_);
   deferred_.emplace_back(
-      [deliverer = MessageDeliverer(std::move(message))](
-          DcSctpSocketCallbacks& cb) mutable { deliverer.Deliver(cb); });
+      +[](CallbackData data, DcSctpSocketCallbacks& cb) {
+        return cb.OnMessageReceived(absl::get<DcSctpMessage>(std::move(data)));
+      },
+      std::move(message));
 }
 
 void CallbackDeferrer::OnError(ErrorKind error, absl::string_view message) {
   RTC_DCHECK(prepared_);
   deferred_.emplace_back(
-      [error, message = std::string(message)](DcSctpSocketCallbacks& cb) {
-        cb.OnError(error, message);
-      });
+      +[](CallbackData data, DcSctpSocketCallbacks& cb) {
+        Error error = absl::get<Error>(std::move(data));
+        return cb.OnError(error.error, error.message);
+      },
+      Error{error, std::string(message)});
 }
 
 void CallbackDeferrer::OnAborted(ErrorKind error, absl::string_view message) {
   RTC_DCHECK(prepared_);
   deferred_.emplace_back(
-      [error, message = std::string(message)](DcSctpSocketCallbacks& cb) {
-        cb.OnAborted(error, message);
-      });
+      +[](CallbackData data, DcSctpSocketCallbacks& cb) {
+        Error error = absl::get<Error>(std::move(data));
+        return cb.OnAborted(error.error, error.message);
+      },
+      Error{error, std::string(message)});
 }
 
 void CallbackDeferrer::OnConnected() {
   RTC_DCHECK(prepared_);
-  deferred_.emplace_back([](DcSctpSocketCallbacks& cb) { cb.OnConnected(); });
+  deferred_.emplace_back(
+      +[](CallbackData data, DcSctpSocketCallbacks& cb) {
+        return cb.OnConnected();
+      },
+      absl::monostate{});
 }
 
 void CallbackDeferrer::OnClosed() {
   RTC_DCHECK(prepared_);
-  deferred_.emplace_back([](DcSctpSocketCallbacks& cb) { cb.OnClosed(); });
+  deferred_.emplace_back(
+      +[](CallbackData data, DcSctpSocketCallbacks& cb) {
+        return cb.OnClosed();
+      },
+      absl::monostate{});
 }
 
 void CallbackDeferrer::OnConnectionRestarted() {
   RTC_DCHECK(prepared_);
   deferred_.emplace_back(
-      [](DcSctpSocketCallbacks& cb) { cb.OnConnectionRestarted(); });
+      +[](CallbackData data, DcSctpSocketCallbacks& cb) {
+        return cb.OnConnectionRestarted();
+      },
+      absl::monostate{});
 }
 
 void CallbackDeferrer::OnStreamsResetFailed(
@@ -125,42 +117,53 @@ void CallbackDeferrer::OnStreamsResetFailed(
     absl::string_view reason) {
   RTC_DCHECK(prepared_);
   deferred_.emplace_back(
-      [streams = std::vector<StreamID>(outgoing_streams.begin(),
-                                       outgoing_streams.end()),
-       reason = std::string(reason)](DcSctpSocketCallbacks& cb) {
-        cb.OnStreamsResetFailed(streams, reason);
-      });
+      +[](CallbackData data, DcSctpSocketCallbacks& cb) {
+        StreamReset stream_reset = absl::get<StreamReset>(std::move(data));
+        return cb.OnStreamsResetFailed(stream_reset.streams,
+                                       stream_reset.message);
+      },
+      StreamReset{{outgoing_streams.begin(), outgoing_streams.end()},
+                  std::string(reason)});
 }
 
 void CallbackDeferrer::OnStreamsResetPerformed(
     rtc::ArrayView<const StreamID> outgoing_streams) {
   RTC_DCHECK(prepared_);
   deferred_.emplace_back(
-      [streams = std::vector<StreamID>(outgoing_streams.begin(),
-                                       outgoing_streams.end())](
-          DcSctpSocketCallbacks& cb) { cb.OnStreamsResetPerformed(streams); });
+      +[](CallbackData data, DcSctpSocketCallbacks& cb) {
+        StreamReset stream_reset = absl::get<StreamReset>(std::move(data));
+        return cb.OnStreamsResetPerformed(stream_reset.streams);
+      },
+      StreamReset{{outgoing_streams.begin(), outgoing_streams.end()}});
 }
 
 void CallbackDeferrer::OnIncomingStreamsReset(
     rtc::ArrayView<const StreamID> incoming_streams) {
   RTC_DCHECK(prepared_);
   deferred_.emplace_back(
-      [streams = std::vector<StreamID>(incoming_streams.begin(),
-                                       incoming_streams.end())](
-          DcSctpSocketCallbacks& cb) { cb.OnIncomingStreamsReset(streams); });
+      +[](CallbackData data, DcSctpSocketCallbacks& cb) {
+        StreamReset stream_reset = absl::get<StreamReset>(std::move(data));
+        return cb.OnIncomingStreamsReset(stream_reset.streams);
+      },
+      StreamReset{{incoming_streams.begin(), incoming_streams.end()}});
 }
 
 void CallbackDeferrer::OnBufferedAmountLow(StreamID stream_id) {
   RTC_DCHECK(prepared_);
-  deferred_.emplace_back([stream_id](DcSctpSocketCallbacks& cb) {
-    cb.OnBufferedAmountLow(stream_id);
-  });
+  deferred_.emplace_back(
+      +[](CallbackData data, DcSctpSocketCallbacks& cb) {
+        return cb.OnBufferedAmountLow(absl::get<StreamID>(std::move(data)));
+      },
+      stream_id);
 }
 
 void CallbackDeferrer::OnTotalBufferedAmountLow() {
   RTC_DCHECK(prepared_);
   deferred_.emplace_back(
-      [](DcSctpSocketCallbacks& cb) { cb.OnTotalBufferedAmountLow(); });
+      +[](CallbackData data, DcSctpSocketCallbacks& cb) {
+        return cb.OnTotalBufferedAmountLow();
+      },
+      absl::monostate{});
 }
 
 void CallbackDeferrer::OnLifecycleMessageExpired(LifecycleId lifecycle_id,

net/dcsctp/socket/callback_deferrer.h

@@ -18,6 +18,7 @@
 #include <vector>
 
 #include "absl/strings/string_view.h"
+#include "absl/types/variant.h"
 #include "api/array_view.h"
 #include "api/ref_counted_base.h"
 #include "api/scoped_refptr.h"
@@ -89,12 +90,26 @@ class CallbackDeferrer : public DcSctpSocketCallbacks {
   void OnLifecycleEnd(LifecycleId lifecycle_id) override;
 
  private:
+  struct Error {
+    ErrorKind error;
+    std::string message;
+  };
+  struct StreamReset {
+    std::vector<StreamID> streams;
+    std::string message;
+  };
+  // Use a pre-sized variant for storage to avoid double heap allocation. This
+  // variant can hold all cases of stored data.
+  using CallbackData = absl::
+      variant<absl::monostate, DcSctpMessage, Error, StreamReset, StreamID>;
+  using Callback = void (*)(CallbackData, DcSctpSocketCallbacks&);
+
   void Prepare();
   void TriggerDeferred();
 
   DcSctpSocketCallbacks& underlying_;
   bool prepared_ = false;
-  std::vector<std::function<void(DcSctpSocketCallbacks& cb)>> deferred_;
+  std::vector<std::pair<Callback, CallbackData>> deferred_;
 };
 }  // namespace dcsctp