From 2a4ad2c8ddc1eb1be8b7ffb607de954ccc2b666e Mon Sep 17 00:00:00 2001
From: Dan Melnic <dmm@fb.com>
Date: Tue, 9 Jan 2018 11:36:55 -0800
Subject: [PATCH] Return if we handle any error messages to avoid unnecessarily
 calling recv/send

Summary: Return if we handle any error messages to avoid unnecessarily calling recv/send

Reviewed By: yfeldblum

Differential Revision: D6677314

fbshipit-source-id: 21f724bb2c92b954888ba97bf7820d72decd2775
---
 folly/io/async/AsyncSocket.cpp | 20 ++++++++++++++------
 folly/io/async/AsyncSocket.h   |  5 ++---
 2 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/folly/io/async/AsyncSocket.cpp b/folly/io/async/AsyncSocket.cpp
index 883ee1d7..3065c1cd 100644
--- a/folly/io/async/AsyncSocket.cpp
+++ b/folly/io/async/AsyncSocket.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright 2017 Facebook, Inc.
+ * Copyright 2017-present Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -13,7 +13,6 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-
 #include <folly/io/async/AsyncSocket.h>
 
 #include <folly/ExceptionWrapper.h>
@@ -1672,7 +1671,11 @@ void AsyncSocket::ioReady(uint16_t events) noexcept {
   // EventHandler::WRITE is set. Any of these flags can
   // indicate that there are messages available in the socket
   // error message queue.
-  handleErrMessages();
+  // Return if we handle any error messages - this is to avoid
+  // unnecessary read/write calls
+  if (handleErrMessages()) {
+    return;
+  }
 
   // Return now if handleErrMessages() detached us from our EventBase
   if (eventBase_ != originalEventBase) {
@@ -1746,7 +1749,7 @@ void AsyncSocket::prepareReadBuffer(void** buf, size_t* buflen) {
   readCallback_->getReadBuffer(buf, buflen);
 }
 
-void AsyncSocket::handleErrMessages() noexcept {
+size_t AsyncSocket::handleErrMessages() noexcept {
   // This method has non-empty implementation only for platforms
   // supporting per-socket error queues.
   VLOG(5) << "AsyncSocket::handleErrMessages() this=" << this << ", fd=" << fd_
@@ -1754,7 +1757,7 @@ void AsyncSocket::handleErrMessages() noexcept {
   if (errMessageCallback_ == nullptr && idZeroCopyBufPtrMap_.empty()) {
     VLOG(7) << "AsyncSocket::handleErrMessages(): "
             << "no callback installed - exiting.";
-    return;
+    return 0;
   }
 
 #ifdef FOLLY_HAVE_MSG_ERRQUEUE
@@ -1774,6 +1777,7 @@ void AsyncSocket::handleErrMessages() noexcept {
   msg.msg_flags = 0;
 
   int ret;
+  size_t num = 0;
   while (true) {
     ret = recvmsg(fd_, &msg, MSG_ERRQUEUE);
     VLOG(5) << "AsyncSocket::handleErrMessages(): recvmsg returned " << ret;
@@ -1789,12 +1793,14 @@ void AsyncSocket::handleErrMessages() noexcept {
           errnoCopy);
         failErrMessageRead(__func__, ex);
       }
-      return;
+
+      return num;
     }
 
     for (struct cmsghdr* cmsg = CMSG_FIRSTHDR(&msg);
          cmsg != nullptr && cmsg->cmsg_len != 0;
          cmsg = CMSG_NXTHDR(&msg, cmsg)) {
+      ++num;
       if (isZeroCopyMsg(*cmsg)) {
         processZeroCopyMsg(*cmsg);
       } else {
@@ -1804,6 +1810,8 @@ void AsyncSocket::handleErrMessages() noexcept {
       }
     }
   }
+#else
+  return 0;
 #endif // FOLLY_HAVE_MSG_ERRQUEUE
 }
 
diff --git a/folly/io/async/AsyncSocket.h b/folly/io/async/AsyncSocket.h
index 44ae5968..c85ac6b8 100644
--- a/folly/io/async/AsyncSocket.h
+++ b/folly/io/async/AsyncSocket.h
@@ -1,5 +1,5 @@
 /*
- * Copyright 2017 Facebook, Inc.
+ * Copyright 2017-present Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -13,7 +13,6 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-
 #pragma once
 
 #include <folly/Optional.h>
@@ -1023,7 +1022,7 @@ class AsyncSocket : virtual public AsyncTransportWrapper {
   virtual void checkForImmediateRead() noexcept;
   virtual void handleInitialReadWrite() noexcept;
   virtual void prepareReadBuffer(void** buf, size_t* buflen);
-  virtual void handleErrMessages() noexcept;
+  virtual size_t handleErrMessages() noexcept;
   virtual void handleRead() noexcept;
   virtual void handleWrite() noexcept;
   virtual void handleConnect() noexcept;
-- 
2.34.1