From d02ff9fd317abc2ca4e8f2d45c3b37b47c4ce0ff Mon Sep 17 00:00:00 2001
From: Christopher Kohlhoff <chris@kohlhoff.com>
Date: Mon, 14 Jan 2008 13:24:28 +0000
Subject: [PATCH] Don't call epoll_wait/kevent if there are no old operations
 (where old means added prior to the last epoll_wait/kevent call) needing to
 be demultiplexed.

[SVN r42755]
---
 include/boost/asio/detail/epoll_reactor.hpp  | 14 ++++++++++++--
 include/boost/asio/detail/kqueue_reactor.hpp | 14 ++++++++++++--
 2 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/include/boost/asio/detail/epoll_reactor.hpp b/include/boost/asio/detail/epoll_reactor.hpp
index 6cd72523..3fa36efa 100644
--- a/include/boost/asio/detail/epoll_reactor.hpp
+++ b/include/boost/asio/detail/epoll_reactor.hpp
@@ -67,7 +67,8 @@ public:
       pending_cancellations_(),
       stop_thread_(false),
       thread_(0),
-      shutdown_(false)
+      shutdown_(false),
+      need_epoll_wait_(true)
   {
     // Start the reactor's internal thread only if needed.
     if (Own_Thread)
@@ -388,7 +389,9 @@ private:
 
     // Block on the epoll descriptor.
     epoll_event events[128];
-    int num_events = epoll_wait(epoll_fd_, events, 128, timeout);
+    int num_events = (block || need_epoll_wait_)
+      ? epoll_wait(epoll_fd_, events, 128, timeout)
+      : 0;
 
     lock.lock();
     wait_in_progress_ = false;
@@ -479,6 +482,10 @@ private:
       cancel_ops_unlocked(pending_cancellations_[i]);
     pending_cancellations_.clear();
 
+    // Determine whether epoll_wait should be called when the reactor next runs.
+    need_epoll_wait_ = !read_op_queue_.empty()
+      || !write_op_queue_.empty() || !except_op_queue_.empty();
+
     cleanup_operations_and_timers(lock);
   }
 
@@ -633,6 +640,9 @@ private:
 
   // Whether the service has been shut down.
   bool shutdown_;
+
+  // Whether we need to call epoll_wait the next time the reactor is run.
+  bool need_epoll_wait_;
 };
 
 } // namespace detail
diff --git a/include/boost/asio/detail/kqueue_reactor.hpp b/include/boost/asio/detail/kqueue_reactor.hpp
index c4668e7a..04261e83 100644
--- a/include/boost/asio/detail/kqueue_reactor.hpp
+++ b/include/boost/asio/detail/kqueue_reactor.hpp
@@ -75,7 +75,8 @@ public:
       pending_cancellations_(),
       stop_thread_(false),
       thread_(0),
-      shutdown_(false)
+      shutdown_(false),
+      need_kqueue_wait_(true)
   {
     // Start the reactor's internal thread only if needed.
     if (Own_Thread)
@@ -374,7 +375,9 @@ private:
 
     // Block on the kqueue descriptor.
     struct kevent events[128];
-    int num_events = kevent(kqueue_fd_, 0, 0, events, 128, timeout);
+    int num_events = (block || need_kqueue_wait_)
+      ? kevent(kqueue_fd_, 0, 0, events, 128, timeout)
+      : 0;
 
     lock.lock();
     wait_in_progress_ = false;
@@ -479,6 +482,10 @@ private:
       cancel_ops_unlocked(pending_cancellations_[i]);
     pending_cancellations_.clear();
 
+    // Determine whether kqueue needs to be called next time the reactor is run.
+    need_kqueue_wait_ = !read_op_queue_.empty()
+      || !write_op_queue_.empty() || !except_op_queue_.empty();
+
     cleanup_operations_and_timers(lock);
   }
 
@@ -631,6 +638,9 @@ private:
 
   // Whether the service has been shut down.
   bool shutdown_;
+
+  // Whether we need to call kqueue the next time the reactor is run.
+  bool need_kqueue_wait_;
 };
 
 } // namespace detail