Command are now stored in ypipes instead of in socketpairs

Storing commands in OS socket buffers caused whole lot of
problems when free space in the buffer ran out. This patch
stores commands in ypipes instead and uses socketpair just
to signal the other thread, ie. at most one byte is stored
in the socketpair at any single instant.

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

7 files changed, 458 insertions, 422 deletions

diff --git a/src/Makefile.am b/src/Makefile.am
index 45e8ac0..9c2fbf1 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -60,6 +60,7 @@ libzmq_la_SOURCES = \
     select.hpp \
     semaphore.hpp \
     session.hpp \
+    signaler.hpp \
     socket_base.hpp \
     stdint.hpp \
     sub.hpp \
@@ -123,6 +124,7 @@ libzmq_la_SOURCES = \
     router.cpp \
     select.cpp \
     session.cpp \
+    signaler.cpp \
     socket_base.cpp \
     sub.cpp \
     tcp_connecter.cpp \
diff --git a/src/config.hpp b/src/config.hpp
index dff3f87..3984fcf 100644
--- a/src/config.hpp
+++ b/src/config.hpp
@@ -36,6 +36,9 @@ namespace zmq
         //  memory allocation by approximately 99.6%
         message_pipe_granularity = 256,
 
+        //  Commands in pipe per allocation event.
+        command_pipe_granularity = 16,
+
         //  Size in bytes of the largest message that is still copied around
         //  rather than being reference-counted.
         max_vsm_size = 29,
diff --git a/src/mailbox.cpp b/src/mailbox.cpp
index 7fdb93e..9ef3e19 100644
--- a/src/mailbox.cpp
+++ b/src/mailbox.cpp
@@ -18,439 +18,64 @@
     along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
-#include "platform.hpp"
-
-#if defined ZMQ_FORCE_SELECT
-#define ZMQ_RCVTIMEO_BASED_ON_SELECT
-#elif defined ZMQ_FORCE_POLL
-#define ZMQ_RCVTIMEO_BASED_ON_POLL
-#elif defined ZMQ_HAVE_LINUX || defined ZMQ_HAVE_FREEBSD ||\
-    defined ZMQ_HAVE_OPENBSD || defined ZMQ_HAVE_SOLARIS ||\
-    defined ZMQ_HAVE_OSX || defined ZMQ_HAVE_QNXNTO ||\
-    defined ZMQ_HAVE_HPUX || defined ZMQ_HAVE_AIX ||\
-    defined ZMQ_HAVE_NETBSD
-#define ZMQ_RCVTIMEO_BASED_ON_POLL
-#elif defined ZMQ_HAVE_WINDOWS || defined ZMQ_HAVE_OPENVMS
-#define ZMQ_RCVTIMEO_BASED_ON_SELECT
-#endif
-
-//  On AIX, poll.h has to be included before zmq.h to get consistent
-//  definition of pollfd structure (AIX uses 'reqevents' and 'retnevents'
-//  instead of 'events' and 'revents' and defines macros to map from POSIX-y
-//  names to AIX-specific names).
-#if defined ZMQ_RCVTIMEO_BASED_ON_POLL
-#include <poll.h>
-#elif defined ZMQ_RCVTIMEO_BASED_ON_SELECT
-#if defined ZMQ_HAVE_WINDOWS
-#include "windows.hpp"
-#elif defined ZMQ_HAVE_HPUX
-#include <sys/param.h>
-#include <sys/types.h>
-#include <sys/time.h>
-#elif defined ZMQ_HAVE_OPENVMS
-#include <sys/types.h>
-#include <sys/time.h>
-#else
-#include <sys/select.h>
-#endif
-#endif
-
 #include "mailbox.hpp"
 #include "err.hpp"
-#include "fd.hpp"
-#include "ip.hpp"
-
-#if defined ZMQ_HAVE_WINDOWS
-#include "windows.hpp"
-#else
-#include <unistd.h>
-#include <fcntl.h>
-#include <limits.h>
-#include <netinet/tcp.h>
-#include <unistd.h>
-#include <sys/types.h>
-#include <sys/socket.h>
-#endif
-
-zmq::fd_t zmq::mailbox_t::get_fd ()
-{
-    return r;
-}
-
-#if defined ZMQ_HAVE_WINDOWS
 
-zmq::mailbox_t::mailbox_t () :
-    blocking (true)
+zmq::mailbox_t::mailbox_t ()
 {
-    //  Create the socketpair for signalling.
-    int rc = make_socketpair (&r, &w);
-    errno_assert (rc == 0);
-
-    //  Set the writer to non-blocking mode.
-    unsigned long argp = 1;
-    rc = ioctlsocket (w, FIONBIO, &argp);
-    wsa_assert (rc != SOCKET_ERROR);
+    //  Get the pipe into passive state. That way, if the users starts by
+    //  polling on the associated file descriptor it will get woken up when
+    //  new command is posted.
+    bool ok = cpipe.read (NULL);
+    zmq_assert (!ok);
+    active = false;
 }
 
 zmq::mailbox_t::~mailbox_t ()
 {
-    int rc = closesocket (w);
-    wsa_assert (rc != SOCKET_ERROR);
-
-    rc = closesocket (r);
-    wsa_assert (rc != SOCKET_ERROR);
-}
-
-void zmq::mailbox_t::send (const command_t &cmd_)
-{
-    //  TODO: Implement SNDBUF auto-resizing as for POSIX platforms.
-    //  In the mean time, the following code with assert if the send()
-    //  call would block.
-    int nbytes = ::send (w, (char *)&cmd_, sizeof (command_t), 0);
-    wsa_assert (nbytes != SOCKET_ERROR);
-    zmq_assert (nbytes == sizeof (command_t));
+    //  TODO: Retrieve and deallocate commands inside the cpipe.
 }
 
-int zmq::mailbox_t::recv (command_t *cmd_, int timeout_)
-{
-    //  If there's a finite timeout, poll on the fd.
-    if (timeout_ > 0)
-        return recv_timeout (cmd_, timeout_);
-
-    //  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.
-    int nbytes = ::recv (r, (char*) cmd_, sizeof (command_t), 0);
-    if (nbytes == -1 && WSAGetLastError () == WSAEWOULDBLOCK) {
-        errno = EAGAIN;
-        return -1;
-    }
-
-    //  Sanity check for success.
-    wsa_assert (nbytes != SOCKET_ERROR);
-
-    //  Check whether we haven't got half of command.
-    zmq_assert (nbytes == sizeof (command_t));
-
-    return 0;
-}
-
-#else
-
-zmq::mailbox_t::mailbox_t () :
-    blocking (true)
-{
-#ifdef PIPE_BUF
-    //  Make sure that command can be written to the socket in atomic fashion.
-    //  If this wasn't guaranteed, commands from different threads would be
-    //  interleaved.
-    zmq_assert (sizeof (command_t) <= PIPE_BUF);
-#endif
-
-    //  Create the socketpair for signaling.
-    int rc = make_socketpair (&r, &w);
-    errno_assert (rc == 0);
-
-    //  Set the writer to non-blocking mode.
-    int flags = fcntl (w, F_GETFL, 0);
-    errno_assert (flags >= 0);
-    rc = fcntl (w, F_SETFL, flags | O_NONBLOCK);
-    errno_assert (rc == 0);
-}
-
-zmq::mailbox_t::~mailbox_t ()
+zmq::fd_t zmq::mailbox_t::get_fd ()
 {
-    close (w);
-    close (r);
+    return signaler.get_fd ();
 }
 
 void zmq::mailbox_t::send (const command_t &cmd_)
 {
-    //  Attempt to write an entire command without blocking.
-    ssize_t nbytes;
-    do {
-        nbytes = ::send (w, &cmd_, sizeof (command_t), 0);
-    } while (nbytes == -1 && errno == EINTR);
-
-    //  Attempt to increase mailbox SNDBUF if the send failed.
-    if (nbytes == -1 && errno == EAGAIN) {
-        int old_sndbuf, new_sndbuf;
-        socklen_t sndbuf_size = sizeof old_sndbuf;
-
-        //  Retrieve current send buffer size.
-        int rc = getsockopt (w, SOL_SOCKET, SO_SNDBUF, &old_sndbuf,
-            &sndbuf_size);
-        errno_assert (rc == 0);
-        new_sndbuf = old_sndbuf * 2;
-
-        //  Double the new send buffer size.
-        rc = setsockopt (w, SOL_SOCKET, SO_SNDBUF, &new_sndbuf, sndbuf_size);
-        errno_assert (rc == 0);
-
-        //  Verify that the OS actually honored the request.
-        rc = getsockopt (w, SOL_SOCKET, SO_SNDBUF, &new_sndbuf, &sndbuf_size);
-        errno_assert (rc == 0);
-        zmq_assert (new_sndbuf > old_sndbuf);
-
-        //  Retry the sending operation; at this point it must succeed.
-        do {
-            nbytes = ::send (w, &cmd_, sizeof (command_t), 0);
-        } while (nbytes == -1 && errno == EINTR);
-    }
-    errno_assert (nbytes != -1);
-
-    //  This should never happen as we've already checked that command size is
-    //  less than PIPE_BUF.
-    zmq_assert (nbytes == sizeof (command_t));
+    sync.lock ();
+    cpipe.write (cmd_, false);
+    bool ok = cpipe.flush ();
+    sync.unlock ();
+    if (!ok)
+        signaler.send ();
 }
 
 int zmq::mailbox_t::recv (command_t *cmd_, int timeout_)
 {
-    //  If there's a finite timeout, poll on the fd.
-    if (timeout_ > 0)
-        return recv_timeout (cmd_, timeout_);
-
-#ifdef MSG_DONTWAIT
-
-    //  Attempt to read an entire command. Returns EAGAIN if non-blocking
-    //  mode is requested and a command is not available.
-    ssize_t nbytes = ::recv (r, cmd_, sizeof (command_t),
-        timeout_ < 0 ? 0 : MSG_DONTWAIT);
-    if (nbytes == -1 && (errno == EAGAIN || errno == EINTR))
-        return -1;
-#else
-
-    //  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,
-            blocking ? flags | O_NONBLOCK : flags & ~O_NONBLOCK);
-        errno_assert (rc == 0);
+    //  Try to get the command straight away.
+    if (active) {
+        bool ok = cpipe.read (cmd_);
+        if (ok)
+            return 0;
+
+        //  If there are no more commands available, switch into passive state.
+        active = false;
+        signaler.recv ();
     }
 
-    //  Attempt to read an entire command.
-    ssize_t nbytes = ::recv (r, cmd_, sizeof (command_t), 0);
-    if (nbytes == -1 && (errno == EAGAIN || errno == EINTR))  
+    //  Wait for signal from the command sender.
+    int rc = signaler.wait (timeout_);
+    if (rc != 0 && errno == EAGAIN)
         return -1;
 
-#endif
-
-    //  Sanity check for success.
-    errno_assert (nbytes != -1);
-
-    //  Check whether we haven't got half of command.
-    zmq_assert (nbytes == sizeof (command_t));
-
-    return 0;
-}
-
-#endif
-
-int zmq::mailbox_t::make_socketpair (fd_t *r_, fd_t *w_)
-{
-#if defined ZMQ_HAVE_WINDOWS
-
-    //  Windows has no 'socketpair' function. CreatePipe is no good as pipe
-    //  handles cannot be polled on. Here we create the socketpair by hand.
-    *w_ = INVALID_SOCKET;
-    *r_ = INVALID_SOCKET;
-
-    //  Create listening socket.
-    SOCKET listener;
-    listener = socket (AF_INET, SOCK_STREAM, 0);
-    wsa_assert (listener != INVALID_SOCKET);
-
-    //  Set SO_REUSEADDR and TCP_NODELAY on listening socket.
-    BOOL so_reuseaddr = 1;
-    int rc = setsockopt (listener, SOL_SOCKET, SO_REUSEADDR,
-        (char *)&so_reuseaddr, sizeof (so_reuseaddr));
-    wsa_assert (rc != SOCKET_ERROR);
-    BOOL tcp_nodelay = 1;
-    rc = setsockopt (listener, IPPROTO_TCP, TCP_NODELAY,
-        (char *)&tcp_nodelay, sizeof (tcp_nodelay));
-    wsa_assert (rc != SOCKET_ERROR);
-
-    //  Bind listening socket to any free local port.
-    struct sockaddr_in addr;
-    memset (&addr, 0, sizeof (addr));
-    addr.sin_family = AF_INET;
-    addr.sin_addr.s_addr = htonl (INADDR_LOOPBACK);
-    addr.sin_port = 0;
-    rc = bind (listener, (const struct sockaddr*) &addr, sizeof (addr));
-    wsa_assert (rc != SOCKET_ERROR);
-
-    //  Retrieve local port listener is bound to (into addr).
-    int addrlen = sizeof (addr);
-    rc = getsockname (listener, (struct sockaddr*) &addr, &addrlen);
-    wsa_assert (rc != SOCKET_ERROR);
-
-    //  Listen for incomming connections.
-    rc = listen (listener, 1);
-    wsa_assert (rc != SOCKET_ERROR);
-
-    //  Create the writer socket.
-    *w_ = WSASocket (AF_INET, SOCK_STREAM, 0, NULL, 0,  0);
-    wsa_assert (*w_ != INVALID_SOCKET);
-
-    //  Set TCP_NODELAY on writer socket.
-    rc = setsockopt (*w_, IPPROTO_TCP, TCP_NODELAY,
-        (char *)&tcp_nodelay, sizeof (tcp_nodelay));
-    wsa_assert (rc != SOCKET_ERROR);
-
-    //  Connect writer to the listener.
-    rc = connect (*w_, (sockaddr *) &addr, sizeof (addr));
-    wsa_assert (rc != SOCKET_ERROR);
-
-    //  Accept connection from writer.
-    *r_ = accept (listener, NULL, NULL);
-    wsa_assert (*r_ != INVALID_SOCKET);
-
-    //  We don't need the listening socket anymore. Close it.
-    rc = closesocket (listener);
-    wsa_assert (rc != SOCKET_ERROR);
-
-    return 0;
-
-#elif defined ZMQ_HAVE_OPENVMS
-
-    //  Whilst OpenVMS supports socketpair - it maps to AF_INET only.  Further,
-    //  it does not set the socket options TCP_NODELAY and TCP_NODELACK which
-    //  can lead to performance problems.
-    //
-    //  The bug will be fixed in V5.6 ECO4 and beyond.  In the meantime, we'll
-    //  create the socket pair manually.
-    sockaddr_in lcladdr;
-    memset (&lcladdr, 0, sizeof (lcladdr));
-    lcladdr.sin_family = AF_INET;
-    lcladdr.sin_addr.s_addr = htonl (INADDR_LOOPBACK);
-    lcladdr.sin_port = 0;
-
-    int listener = socket (AF_INET, SOCK_STREAM, 0);
-    errno_assert (listener != -1);
-
-    int on = 1;
-    int rc = setsockopt (listener, IPPROTO_TCP, TCP_NODELAY, &on, sizeof (on));
-    errno_assert (rc != -1);
-
-    rc = setsockopt (listener, IPPROTO_TCP, TCP_NODELACK, &on, sizeof (on));
-    errno_assert (rc != -1);
-
-    rc = bind(listener, (struct sockaddr*) &lcladdr, sizeof (lcladdr));
-    errno_assert (rc != -1);
-
-    socklen_t lcladdr_len = sizeof (lcladdr);
-
-    rc = getsockname (listener, (struct sockaddr*) &lcladdr, &lcladdr_len);
-    errno_assert (rc != -1);
-
-    rc = listen (listener, 1);
-    errno_assert (rc != -1);
-
-    *w_ = socket (AF_INET, SOCK_STREAM, 0);
-    errno_assert (*w_ != -1);
-
-    rc = setsockopt (*w_, IPPROTO_TCP, TCP_NODELAY, &on, sizeof (on));
-    errno_assert (rc != -1);
-
-    rc = setsockopt (*w_, IPPROTO_TCP, TCP_NODELACK, &on, sizeof (on));
-    errno_assert (rc != -1);
+    //  We've got the signal. Now we can switch into active state.
+    active = true;
 
-    rc = connect (*w_, (struct sockaddr*) &lcladdr, sizeof (lcladdr));
-    errno_assert (rc != -1);
-
-    *r_ = accept (listener, NULL, NULL);
-    errno_assert (*r_ != -1);
-
-    close (listener);
-
-    return 0;
-
-#else // All other implementations support socketpair()
-
-    int sv [2];
-    int rc = socketpair (AF_UNIX, SOCK_STREAM, 0, sv);
+    //  Get a command.
     errno_assert (rc == 0);
-    *w_ = sv [0];
-    *r_ = sv [1];
+    bool ok = cpipe.read (cmd_);
+    zmq_assert (ok);
     return 0;
-
-#endif
 }
 
-int zmq::mailbox_t::recv_timeout (command_t *cmd_, int timeout_)
-{
-#ifdef ZMQ_RCVTIMEO_BASED_ON_POLL
-
-    struct pollfd pfd;
-    pfd.fd = r;
-    pfd.events = POLLIN;
-    int rc = poll (&pfd, 1, timeout_);
-    if (unlikely (rc < 0)) {
-        zmq_assert (errno == EINTR);
-        return -1;
-    }
-    else if (unlikely (rc == 0)) {
-        errno = EAGAIN;
-        return -1;
-    }
-    zmq_assert (rc == 1);
-    zmq_assert (pfd.revents & POLLIN);
-
-#elif defined ZMQ_RCVTIMEO_BASED_ON_SELECT
-
-    fd_set fds;
-    FD_ZERO (&fds);
-    FD_SET (r, &fds);
-    struct timeval timeout;
-    timeout.tv_sec = timeout_ / 1000;
-    timeout.tv_usec = timeout_ % 1000 * 1000;
-#ifdef ZMQ_HAVE_WINDOWS
-    int rc = select (0, &fds, NULL, NULL, &timeout);
-    wsa_assert (rc != SOCKET_ERROR);
-#else
-    int rc = select (r + 1, &fds, NULL, NULL, &timeout);
-    if (unlikely (rc < 0)) {
-        zmq_assert (errno == EINTR);
-        return -1;
-    }
-#endif
-    if (unlikely (rc == 0)) {
-        errno = EAGAIN;
-        return -1;
-    }
-    zmq_assert (rc == 1);
-
-
-#else
-#error
-#endif
-
-    //  The file descriptor is ready for reading. Extract one command out of it.
-#ifdef ZMQ_HAVE_WINDOWS
-    int nbytes = ::recv (r, (char*) cmd_, sizeof (command_t), 0);
-    wsa_assert (nbytes != SOCKET_ERROR);
-#else
-    ssize_t nbytes = ::recv (r, cmd_, sizeof (command_t), 0);
-    if (unlikely (rc < 0 && errno == EINTR))
-        return -1;
-    errno_assert (nbytes > 0);
-#endif
-    zmq_assert (nbytes == sizeof (command_t));
-    return 0;
-}
-
-#if defined ZMQ_RCVTIMEO_BASED_ON_SELECT
-#undef ZMQ_RCVTIMEO_BASED_ON_SELECT
-#endif
-#if defined ZMQ_RCVTIMEO_BASED_ON_POLL
-#undef ZMQ_RCVTIMEO_BASED_ON_POLL
-#endif
-
diff --git a/src/mailbox.hpp b/src/mailbox.hpp
index eb02e39..0675b99 100644
--- a/src/mailbox.hpp
+++ b/src/mailbox.hpp
@@ -24,10 +24,12 @@
 #include <stddef.h>
 
 #include "platform.hpp"
+#include "signaler.hpp"
 #include "fd.hpp"
-#include "stdint.hpp"
 #include "config.hpp"
 #include "command.hpp"
+#include "ypipe.hpp"
+#include "mutex.hpp"
 
 namespace zmq
 {
@@ -45,21 +47,22 @@ namespace zmq
         
     private:
 
-        //  Platform-dependent function to create a socketpair.
-        static int make_socketpair (fd_t *r_, fd_t *w_);
+        //  The pipe to store actual commands.
+        typedef ypipe_t <command_t, command_pipe_granularity> cpipe_t;
+        cpipe_t cpipe;
 
-        //  Receives a command with the specific timeout.
-        //  This function is not to be used for non-blocking or inifinitely
-        //  blocking recvs.
-        int recv_timeout (command_t *cmd_, int timeout_);
+        //  Signaler to pass signals from writer thread to reader thread.
+        signaler_t signaler;
 
-        //  Write & read end of the socketpair.
-        fd_t w;
-        fd_t r;
+        //  There's only one thread receiving from the mailbox, but there
+        //  is arbitrary number of threads sending. Given that ypipe requires
+        //  synchronised access on both of its endpoints, we have to synchronise
+        //  the sending side.
+        mutex_t sync;
 
-        //  Used on platforms where there's no MSG_DONTWAIT functionality.
-        //  True if the read socket is set to the blocking state.
-        bool blocking;
+        //  True if the underlying pipe is active, ie. when we are allowed to
+        //  read commands from it.
+        bool active;
 
         //  Disable copying of mailbox_t object.
         mailbox_t (const mailbox_t&);
diff --git a/src/signaler.cpp b/src/signaler.cpp
new file mode 100644
index 0000000..2ecfb98
--- /dev/null
+++ b/src/signaler.cpp
@@ -0,0 +1,340 @@
+/*
+    Copyright (c) 2007-2011 iMatix Corporation
+    Copyright (c) 2007-2011 Other contributors as noted in the AUTHORS file
+
+    This file is part of 0MQ.
+
+    0MQ is free software; you can redistribute it and/or modify it under
+    the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation; either version 3 of the License, or
+    (at your option) any later version.
+
+    0MQ is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Lesser General Public License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "platform.hpp"
+
+#if defined ZMQ_FORCE_SELECT
+#define ZMQ_SIGNALER_WAIT_BASED_ON_SELECT
+#elif defined ZMQ_FORCE_POLL
+#define ZMQ_SIGNALER_WAIT_BASED_ON_POLL
+#elif defined ZMQ_HAVE_LINUX || defined ZMQ_HAVE_FREEBSD ||\
+    defined ZMQ_HAVE_OPENBSD || defined ZMQ_HAVE_SOLARIS ||\
+    defined ZMQ_HAVE_OSX || defined ZMQ_HAVE_QNXNTO ||\
+    defined ZMQ_HAVE_HPUX || defined ZMQ_HAVE_AIX ||\
+    defined ZMQ_HAVE_NETBSD
+#define ZMQ_SIGNALER_WAIT_BASED_ON_POLL
+#elif defined ZMQ_HAVE_WINDOWS || defined ZMQ_HAVE_OPENVMS
+#define ZMQ_SIGNALER_WAIT_BASED_ON_SELECT
+#endif
+
+//  On AIX, poll.h has to be included before zmq.h to get consistent
+//  definition of pollfd structure (AIX uses 'reqevents' and 'retnevents'
+//  instead of 'events' and 'revents' and defines macros to map from POSIX-y
+//  names to AIX-specific names).
+#if defined ZMQ_SIGNALER_WAIT_BASED_ON_POLL
+#include <poll.h>
+#elif defined ZMQ_SIGNALER_WAIT_BASED_ON_SELECT
+#if defined ZMQ_HAVE_WINDOWS
+#include "windows.hpp"
+#elif defined ZMQ_HAVE_HPUX
+#include <sys/param.h>
+#include <sys/types.h>
+#include <sys/time.h>
+#elif defined ZMQ_HAVE_OPENVMS
+#include <sys/types.h>
+#include <sys/time.h>
+#else
+#include <sys/select.h>
+#endif
+#endif
+
+#include "signaler.hpp"
+#include "likely.hpp"
+#include "err.hpp"
+#include "fd.hpp"
+#include "ip.hpp"
+
+#if defined ZMQ_HAVE_WINDOWS
+#include "windows.hpp"
+#else
+#include <unistd.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <netinet/tcp.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#endif
+
+zmq::signaler_t::signaler_t ()
+{
+    //  Create the socketpair for signaling.
+    int rc = make_fdpair (&r, &w);
+    errno_assert (rc == 0);
+
+    //  Set both fds to non-blocking mode.
+#if defined ZMQ_HAVE_WINDOWS
+    unsigned long argp = 1;
+    rc = ioctlsocket (w, FIONBIO, &argp);
+    wsa_assert (rc != SOCKET_ERROR);
+    rc = ioctlsocket (r, FIONBIO, &argp);
+    wsa_assert (rc != SOCKET_ERROR);
+#else
+    int flags = fcntl (w, F_GETFL, 0);
+    errno_assert (flags >= 0);
+    rc = fcntl (w, F_SETFL, flags | O_NONBLOCK);
+    errno_assert (rc == 0);
+    flags = fcntl (r, F_GETFL, 0);
+    errno_assert (flags >= 0);
+    rc = fcntl (r, F_SETFL, flags | O_NONBLOCK);
+    errno_assert (rc == 0);
+#endif
+}
+
+zmq::signaler_t::~signaler_t ()
+{
+#if defined ZMQ_HAVE_WINDOWS
+    int rc = closesocket (w);
+    wsa_assert (rc != SOCKET_ERROR);
+    rc = closesocket (r);
+    wsa_assert (rc != SOCKET_ERROR);
+#else
+    close (w);
+    close (r);
+#endif
+}
+
+zmq::fd_t zmq::signaler_t::get_fd ()
+{
+    return r;
+}
+
+void zmq::signaler_t::send ()
+{
+#if defined ZMQ_HAVE_WINDOWS
+    unsigned char dummy = 0;
+    int nbytes = ::send (w, &dummy, sizeof (dummy), 0);
+    wsa_assert (nbytes != SOCKET_ERROR);
+    zmq_assert (nbytes == sizeof (dummy));
+#else
+    unsigned char dummy = 0;
+    while (true) {
+        ssize_t nbytes = ::send (w, &dummy, sizeof (dummy), 0);
+        if (unlikely (nbytes == -1 && errno == EINTR))
+            continue;
+        zmq_assert (nbytes == sizeof (dummy));
+        break;
+    }
+#endif
+}
+
+int zmq::signaler_t::wait (int timeout_)
+{
+#ifdef ZMQ_SIGNALER_WAIT_BASED_ON_POLL
+
+    struct pollfd pfd;
+    pfd.fd = r;
+    pfd.events = POLLIN;
+    int rc = poll (&pfd, 1, timeout_);
+    if (unlikely (rc < 0)) {
+        zmq_assert (errno == EINTR);
+        return -1;
+    }
+    else if (unlikely (rc == 0)) {
+        errno = EAGAIN;
+        return -1;
+    }
+    zmq_assert (rc == 1);
+    zmq_assert (pfd.revents & POLLIN);
+    return 0;
+
+#elif defined ZMQ_SIGNALER_WAIT_BASED_ON_SELECT
+
+    fd_set fds;
+    FD_ZERO (&fds);
+    FD_SET (r, &fds);
+    struct timeval timeout;
+    timeout.tv_sec = timeout_ / 1000;
+    timeout.tv_usec = timeout_ % 1000 * 1000;
+#ifdef ZMQ_HAVE_WINDOWS
+    int rc = select (0, &fds, NULL, NULL, &timeout);
+    wsa_assert (rc != SOCKET_ERROR);
+#else
+    int rc = select (r + 1, &fds, NULL, NULL, &timeout);
+    if (unlikely (rc < 0)) {
+        zmq_assert (errno == EINTR);
+        return -1;
+    }
+#endif
+    if (unlikely (rc == 0)) {
+        errno = EAGAIN;
+        return -1;
+    }
+    zmq_assert (rc == 1);
+    return 0;
+
+#else
+#error
+#endif
+}
+
+void zmq::signaler_t::recv ()
+{
+    //  Attempt to read a signal.
+    unsigned char dummy;
+#if ZMQ_HAVE_WINDOWS
+    int nbytes = ::recv (r, &dummy, sizeof (dummy), 0);
+    wsa_assert (nbytes != SOCKET_ERROR);
+#else
+    ssize_t nbytes = ::recv (r, &dummy, sizeof (dummy), 0);
+    errno_assert (nbytes >= 0);
+#endif
+    zmq_assert (nbytes == sizeof (dummy));
+    zmq_assert (dummy == 0);
+}
+
+int zmq::signaler_t::make_fdpair (fd_t *r_, fd_t *w_)
+{
+#if defined ZMQ_HAVE_WINDOWS
+
+    //  Windows has no 'socketpair' function. CreatePipe is no good as pipe
+    //  handles cannot be polled on. Here we create the socketpair by hand.
+    *w_ = INVALID_SOCKET;
+    *r_ = INVALID_SOCKET;
+
+    //  Create listening socket.
+    SOCKET listener;
+    listener = socket (AF_INET, SOCK_STREAM, 0);
+    wsa_assert (listener != INVALID_SOCKET);
+
+    //  Set SO_REUSEADDR and TCP_NODELAY on listening socket.
+    BOOL so_reuseaddr = 1;
+    int rc = setsockopt (listener, SOL_SOCKET, SO_REUSEADDR,
+        (char *)&so_reuseaddr, sizeof (so_reuseaddr));
+    wsa_assert (rc != SOCKET_ERROR);
+    BOOL tcp_nodelay = 1;
+    rc = setsockopt (listener, IPPROTO_TCP, TCP_NODELAY,
+        (char *)&tcp_nodelay, sizeof (tcp_nodelay));
+    wsa_assert (rc != SOCKET_ERROR);
+
+    //  Bind listening socket to any free local port.
+    struct sockaddr_in addr;
+    memset (&addr, 0, sizeof (addr));
+    addr.sin_family = AF_INET;
+    addr.sin_addr.s_addr = htonl (INADDR_LOOPBACK);
+    addr.sin_port = 0;
+    rc = bind (listener, (const struct sockaddr*) &addr, sizeof (addr));
+    wsa_assert (rc != SOCKET_ERROR);
+
+    //  Retrieve local port listener is bound to (into addr).
+    int addrlen = sizeof (addr);
+    rc = getsockname (listener, (struct sockaddr*) &addr, &addrlen);
+    wsa_assert (rc != SOCKET_ERROR);
+
+    //  Listen for incomming connections.
+    rc = listen (listener, 1);
+    wsa_assert (rc != SOCKET_ERROR);
+
+    //  Create the writer socket.
+    *w_ = WSASocket (AF_INET, SOCK_STREAM, 0, NULL, 0,  0);
+    wsa_assert (*w_ != INVALID_SOCKET);
+
+    //  Set TCP_NODELAY on writer socket.
+    rc = setsockopt (*w_, IPPROTO_TCP, TCP_NODELAY,
+        (char *)&tcp_nodelay, sizeof (tcp_nodelay));
+    wsa_assert (rc != SOCKET_ERROR);
+
+    //  Connect writer to the listener.
+    rc = connect (*w_, (sockaddr *) &addr, sizeof (addr));
+    wsa_assert (rc != SOCKET_ERROR);
+
+    //  Accept connection from writer.
+    *r_ = accept (listener, NULL, NULL);
+    wsa_assert (*r_ != INVALID_SOCKET);
+
+    //  We don't need the listening socket anymore. Close it.
+    rc = closesocket (listener);
+    wsa_assert (rc != SOCKET_ERROR);
+
+    return 0;
+
+#elif defined ZMQ_HAVE_OPENVMS
+
+    //  Whilst OpenVMS supports socketpair - it maps to AF_INET only.  Further,
+    //  it does not set the socket options TCP_NODELAY and TCP_NODELACK which
+    //  can lead to performance problems.
+    //
+    //  The bug will be fixed in V5.6 ECO4 and beyond.  In the meantime, we'll
+    //  create the socket pair manually.
+    sockaddr_in lcladdr;
+    memset (&lcladdr, 0, sizeof (lcladdr));
+    lcladdr.sin_family = AF_INET;
+    lcladdr.sin_addr.s_addr = htonl (INADDR_LOOPBACK);
+    lcladdr.sin_port = 0;
+
+    int listener = socket (AF_INET, SOCK_STREAM, 0);
+    errno_assert (listener != -1);
+
+    int on = 1;
+    int rc = setsockopt (listener, IPPROTO_TCP, TCP_NODELAY, &on, sizeof (on));
+    errno_assert (rc != -1);
+
+    rc = setsockopt (listener, IPPROTO_TCP, TCP_NODELACK, &on, sizeof (on));
+    errno_assert (rc != -1);
+
+    rc = bind(listener, (struct sockaddr*) &lcladdr, sizeof (lcladdr));
+    errno_assert (rc != -1);
+
+    socklen_t lcladdr_len = sizeof (lcladdr);
+
+    rc = getsockname (listener, (struct sockaddr*) &lcladdr, &lcladdr_len);
+    errno_assert (rc != -1);
+
+    rc = listen (listener, 1);
+    errno_assert (rc != -1);
+
+    *w_ = socket (AF_INET, SOCK_STREAM, 0);
+    errno_assert (*w_ != -1);
+
+    rc = setsockopt (*w_, IPPROTO_TCP, TCP_NODELAY, &on, sizeof (on));
+    errno_assert (rc != -1);
+
+    rc = setsockopt (*w_, IPPROTO_TCP, TCP_NODELACK, &on, sizeof (on));
+    errno_assert (rc != -1);
+
+    rc = connect (*w_, (struct sockaddr*) &lcladdr, sizeof (lcladdr));
+    errno_assert (rc != -1);
+
+    *r_ = accept (listener, NULL, NULL);
+    errno_assert (*r_ != -1);
+
+    close (listener);
+
+    return 0;
+
+#else // All other implementations support socketpair()
+
+    int sv [2];
+    int rc = socketpair (AF_UNIX, SOCK_STREAM, 0, sv);
+    errno_assert (rc == 0);
+    *w_ = sv [0];
+    *r_ = sv [1];
+    return 0;
+
+#endif
+}
+
+#if defined ZMQ_SIGNALER_WAIT_BASED_ON_SELECT
+#undef ZMQ_SIGNALER_WAIT_BASED_ON_SELECT
+#endif
+#if defined ZMQ_SIGNALER_WAIT_BASED_ON_POLL
+#undef ZMQ_SIGNALER_WAIT_BASED_ON_POLL
+#endif
+
diff --git a/src/signaler.hpp b/src/signaler.hpp
new file mode 100644
index 0000000..2ebff41
--- /dev/null
+++ b/src/signaler.hpp
@@ -0,0 +1,63 @@
+/*
+    Copyright (c) 2007-2011 iMatix Corporation
+    Copyright (c) 2007-2011 Other contributors as noted in the AUTHORS file
+
+    This file is part of 0MQ.
+
+    0MQ is free software; you can redistribute it and/or modify it under
+    the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation; either version 3 of the License, or
+    (at your option) any later version.
+
+    0MQ is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Lesser General Public License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef __ZMQ_SIGNALER_HPP_INCLUDED__
+#define __ZMQ_SIGNALER_HPP_INCLUDED__
+
+#include "fd.hpp"
+
+namespace zmq
+{
+
+    //  This is a cross-platform equivalent to signal_fd. However, as opposed
+    //  to signal_fd there can be at most one signal in the signaler at any
+    //  given moment. Attempt to send a signal before receiving the previous
+    //  one will result in undefined behaviour.
+
+    class signaler_t
+    {
+    public:
+
+        signaler_t ();
+        ~signaler_t ();
+
+        fd_t get_fd ();
+        void send ();
+        int wait (int timeout_);
+        void recv ();
+        
+    private:
+
+        //  Creates a pair of filedescriptors that will be used
+        //  to pass the signals.
+        static int make_fdpair (fd_t *r_, fd_t *w_);
+
+        //  Write & read end of the socketpair.
+        fd_t w;
+        fd_t r;
+
+        //  Disable copying of signaler_t object.
+        signaler_t (const signaler_t&);
+        const signaler_t &operator = (const signaler_t&);
+    };
+
+}
+
+#endif
diff --git a/tests/test_shutdown_stress.cpp b/tests/test_shutdown_stress.cpp
index ef81758..b3ee90f 100644
--- a/tests/test_shutdown_stress.cpp
+++ b/tests/test_shutdown_stress.cpp
@@ -23,7 +23,7 @@
 #include <pthread.h>
 #include <stddef.h>
 
-#define THREAD_COUNT 10
+#define THREAD_COUNT 100
 
 extern "C"
 {