Wed Oct 28 19:49:39 UTC 2009 Chris Cleeland <cleeland@ociweb.com>

        * ace/Select_Reactor_Base.h:
        * ace/Select_Reactor_Base.cpp:

          Changed the second recv() that is used in case of a short first
          read to be a recv_n(), blocking until the rest of the buffer can
          be received on the pipe.  The problem was discovered during
          routine testing (Notify_Performance_Test) on VxWorks 6.7 on a P3
          platform, but could occur on any platform. [Bugzilla 3754]

3 files changed, 41 insertions, 3 deletions

diff --git a/ACE/ChangeLog b/ACE/ChangeLog
index c8258699330..2db9d44310a 100644
--- a/ACE/ChangeLog
+++ b/ACE/ChangeLog
@@ -1,3 +1,14 @@
+Wed Oct 28 19:49:39 UTC 2009  Chris Cleeland  <cleeland@ociweb.com>
+
+        * ace/Select_Reactor_Base.h:
+        * ace/Select_Reactor_Base.cpp:
+
+          Changed the second recv() that is used in case of a short first
+          read to be a recv_n(), blocking until the rest of the buffer can
+          be received on the pipe.  The problem was discovered during
+          routine testing (Notify_Performance_Test) on VxWorks 6.7 on a P3
+          platform, but could occur on any platform. [Bugzilla 3754]
+
 Wed Oct 28 11:58:21 UTC 2009  Olli Savia  <ops@iki.fi>
 
         * ace/config-win32-msvc-7.h:
diff --git a/ACE/ace/Select_Reactor_Base.cpp b/ACE/ace/Select_Reactor_Base.cpp
index 771a5b49d90..7f37dc89808 100644
--- a/ACE/ace/Select_Reactor_Base.cpp
+++ b/ACE/ace/Select_Reactor_Base.cpp
@@ -869,6 +869,25 @@ ACE_Select_Reactor_Notify::read_notify_pipe (ACE_HANDLE handle,
 {
   ACE_TRACE ("ACE_Select_Reactor_Notify::read_notify_pipe");
 
+  // This is kind of a weird, fragile beast.  We first read with a
+  // regular read.  The read side of this socket is non-blocking, so
+  // the read may end up being short.
+  //
+  // If the read is short, then we do a recv_n to insure that we block
+  // and read the rest of the buffer.
+  //
+  // Now, you might be tempted to say, "why don't we just replace the
+  // first recv with a recv_n?"  I was, too.  But that doesn't work
+  // because of how the calling code in handle_input() works.  In
+  // handle_input, the event will only be dispatched if the return
+  // value from read_notify_pipe() is > 0.  That means that we can't
+  // return zero from this func unless it's an EOF condition.
+  //
+  // Thus, the return value semantics for this are:
+  // -1: nothing read, fatal, unrecoverable error
+  // 0: nothing read at all
+  // 1: complete buffer read
+
   ssize_t const n = ACE::recv (handle, (char *) &buffer, sizeof buffer);
 
   if (n > 0)
@@ -882,9 +901,9 @@ ACE_Select_Reactor_Notify::read_notify_pipe (ACE_HANDLE handle,
           // doesn't work we're in big trouble since the input stream
           // won't be aligned correctly.  I'm not sure quite what to
           // do at this point.  It's probably best just to return -1.
-          if (ACE::recv (handle,
-                         ((char *) &buffer) + n,
-                         remainder) != remainder)
+          if (ACE::recv_n (handle,
+			   ((char *) &buffer) + n,
+			   remainder) != remainder)
             return -1;
         }
 
@@ -911,6 +930,9 @@ ACE_Select_Reactor_Notify::handle_input (ACE_HANDLE handle)
   int result = 0;
   ACE_Notification_Buffer buffer;
 
+  // If there is only one buffer in the pipe, this will loop and call
+  // read_notify_pipe() twice.  The first time will read the buffer, and
+  // the second will read the fact that the pipe is empty.
   while ((result = this->read_notify_pipe (handle, buffer)) > 0)
     {
       // Dispatch the buffer
diff --git a/ACE/ace/Select_Reactor_Base.h b/ACE/ace/Select_Reactor_Base.h
index 20c1e536e6a..565dd2c4afb 100644
--- a/ACE/ace/Select_Reactor_Base.h
+++ b/ACE/ace/Select_Reactor_Base.h
@@ -180,6 +180,11 @@ public:
   /// Read one of the notify call on the @a handle into the
   /// @a buffer. This could be because of a thread trying to unblock
   /// the Reactor_Impl
+  ///
+  /// Return value semantics for this are:
+  /// -1: nothing read, fatal, unrecoverable error
+  ///  0: nothing read at all
+  ///  1: complete buffer read
   virtual int read_notify_pipe (ACE_HANDLE handle,
                                 ACE_Notification_Buffer &buffer);