Optimise block/non-block switching in mailbox_t

For the platforms that don't support MSG_DONTWAIT the reader
socket in mailbox_t was kept in non-blocking state and flipped
to blocking state and back when blocking read was requested.
Now, the state is preserved between calls and flipped only
if different type of operation (block vs. non-block) is
requested.
Signed-off-by: Fabien Ninoles <fabien@tzone.org>
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

src/mailbox.cpp

@@ -79,7 +79,8 @@ zmq::fd_t zmq::mailbox_t::get_fd ()
 
 #if defined ZMQ_HAVE_WINDOWS
 
-zmq::mailbox_t::mailbox_t ()
+zmq::mailbox_t::mailbox_t () :
+    blocking (true)
 {
     //  Create the socketpair for signalling.
     int rc = make_socketpair (&r, &w);
@@ -89,11 +90,6 @@ zmq::mailbox_t::mailbox_t ()
     unsigned long argp = 1;
     rc = ioctlsocket (w, FIONBIO, &argp);
     wsa_assert (rc != SOCKET_ERROR);
-
-    //  Set the reader to non-blocking mode.
-    argp = 1;
-    rc = ioctlsocket (r, FIONBIO, &argp);
-    wsa_assert (rc != SOCKET_ERROR);
 }
 
 zmq::mailbox_t::~mailbox_t ()
@@ -121,33 +117,18 @@ int zmq::mailbox_t::recv (command_t *cmd_, int timeout_)
     if (timeout_ > 0)
         return recv_timeout (cmd_, timeout_);
 
-    //  If required, set the reader to blocking mode.
-    if (timeout_ < 0) {
-        unsigned long argp = 0;
+    //  If required, switch the reader to blocking or non-blocking mode.
+    if ((timeout_ < 0 && !blocking) || (timeout_ == 0 && blocking)) {
+        blocking = (timeout_ < 0);
+        unsigned long argp = blocking ? 0 : 1;
         int rc = ioctlsocket (r, FIONBIO, &argp);
         wsa_assert (rc != SOCKET_ERROR);
     }
 
-    //  Attempt to read an entire command. Returns EAGAIN if non-blocking
-    //  and a command is not available. Save value of errno if we wish to pass
-    //  it to caller.
-    int err = 0;
+    //  Attempt to read an entire command.
     int nbytes = ::recv (r, (char*) cmd_, sizeof (command_t), 0);
     if (nbytes == -1 && WSAGetLastError () == WSAEWOULDBLOCK)
-        err = EAGAIN;
-
-    //  Re-set the reader to non-blocking mode.
-    if (timeout_ < 0) {
-        unsigned long argp = 1;
-        int rc = ioctlsocket (r, FIONBIO, &argp);
-        wsa_assert (rc != SOCKET_ERROR);
-    }
-
-    //  If the recv failed, return with the saved errno.
-    if (err != 0) {
-        errno = err;
         return -1;
-    }
 
     //  Sanity check for success.
     wsa_assert (nbytes != SOCKET_ERROR);
@@ -160,7 +141,8 @@ int zmq::mailbox_t::recv (command_t *cmd_, int timeout_)
 
 #else
 
-zmq::mailbox_t::mailbox_t ()
+zmq::mailbox_t::mailbox_t () :
+    blocking (true)
 {
 #ifdef PIPE_BUF
     //  Make sure that command can be written to the socket in atomic fashion.
@@ -178,14 +160,6 @@ zmq::mailbox_t::mailbox_t ()
     errno_assert (flags >= 0);
     rc = fcntl (w, F_SETFL, flags | O_NONBLOCK);
     errno_assert (rc == 0);
-
-#ifndef MSG_DONTWAIT
-    //  Set the reader to non-blocking mode.
-    flags = fcntl (r, F_GETFL, 0);
-    errno_assert (flags >= 0);
-    rc = fcntl (r, F_SETFL, flags | O_NONBLOCK);
-    errno_assert (rc == 0);
-#endif
 }
 
 zmq::mailbox_t::~mailbox_t ()
@@ -250,35 +224,20 @@ int zmq::mailbox_t::recv (command_t *cmd_, int timeout_)
         return -1;
 #else
 
-    //  If required, set the reader to blocking mode.
-    if (timeout_ < 0) {
+    //  If required, switch the reader to blocking or non-blocking mode.
+    if ((timeout_ < 0 && !blocking) || (timeout_ == 0 && blocking)) {
+        blocking = (timeout_ < 0);
         int flags = fcntl (r, F_GETFL, 0);
         errno_assert (flags >= 0);
-        int rc = fcntl (r, F_SETFL, flags & ~O_NONBLOCK);
+        int rc = fcntl (r, F_SETFL,
+            blocking ? flags | O_NONBLOCK : flags & ~O_NONBLOCK);
         errno_assert (rc == 0);
     }
 
-    //  Attempt to read an entire command. Returns EAGAIN if non-blocking
-    //  and a command is not available. Save value of errno if we wish to pass
-    //  it to caller.
-    int err = 0;
+    //  Attempt to read an entire command.
     ssize_t nbytes = ::recv (r, cmd_, sizeof (command_t), 0);
     if (nbytes == -1 && (errno == EAGAIN || errno == EINTR))  
-        err = errno;
-
-    //  Re-set the reader to non-blocking mode.
-    if (timeout_ < 0) {
-        int flags = fcntl (r, F_GETFL, 0);
-        errno_assert (flags >= 0);
-        int rc = fcntl (r, F_SETFL, flags | O_NONBLOCK);
-        errno_assert (rc == 0);
-    }
-
-    //  If the recv failed, return with the saved errno if set.
-    if (err != 0) {
-        errno = err;
         return -1;
-    }
 
 #endif
 

src/mailbox.hpp

@@ -45,10 +45,6 @@ namespace zmq
         
     private:
 
-        //  Write & read end of the socketpair.
-        fd_t w;
-        fd_t r;
-
         //  Platform-dependent function to create a socketpair.
         static int make_socketpair (fd_t *r_, fd_t *w_);
 
@@ -57,6 +53,14 @@ namespace zmq
         //  blocking recvs.
         int recv_timeout (command_t *cmd_, int timeout_);
 
+        //  Write & read end of the socketpair.
+        fd_t w;
+        fd_t r;
+
+        //  Used on platforms where there's no MSG_DONTWAIT functionality.
+        //  True if the read socket is set to the blocking state.
+        bool blocking;
+
         //  Disable copying of mailbox_t object.
         mailbox_t (const mailbox_t&);
         const mailbox_t &operator = (const mailbox_t&);