diff --git a/src/mutex.hpp b/src/mutex.hpp
index 82b23632..db5056e4 100644
--- a/src/mutex.hpp
+++ b/src/mutex.hpp
@@ -181,6 +181,33 @@ namespace zmq
         scoped_lock_t (const scoped_lock_t&);
         const scoped_lock_t &operator = (const scoped_lock_t&);
     };
+
+
+    struct scoped_optional_lock_t
+    {
+        scoped_optional_lock_t (mutex_t* mutex_)
+            : mutex (mutex_)
+        {
+            if(mutex != 0)
+                mutex->lock ();
+        }
+
+        ~scoped_optional_lock_t ()
+        {
+            if(mutex != 0)
+                mutex->unlock ();
+        }
+
+    private:
+
+        mutex_t* mutex;
+
+        // Disable copy construction and assignment.
+        scoped_optional_lock_t (const scoped_lock_t&);
+        const scoped_optional_lock_t &operator = (const scoped_lock_t&);
+    };
+
+
 }
 
 #endif
diff --git a/src/socket_base.cpp b/src/socket_base.cpp
index a7d92c72..97b5ac70 100644
--- a/src/socket_base.cpp
+++ b/src/socket_base.cpp
@@ -97,13 +97,7 @@
 #include "scatter.hpp"
 #include "dgram.hpp"
 
-#define ENTER_MUTEX() \
-    if (thread_safe) \
-        sync.lock();
 
-#define EXIT_MUTEX(); \
-    if (thread_safe) \
-        sync.unlock();
 
 bool zmq::socket_base_t::check_tag ()
 {
@@ -338,24 +332,21 @@ void zmq::socket_base_t::attach_pipe (pipe_t *pipe_, bool subscribe_to_all_)
 int zmq::socket_base_t::setsockopt (int option_, const void *optval_,
     size_t optvallen_)
 {
-    ENTER_MUTEX ();
+    scoped_optional_lock_t sync_lock(thread_safe ? &sync : 0);
 
     if (!options.is_valid(option_)) {
         errno = EINVAL;
-        EXIT_MUTEX ();
         return -1;
     }
 
     if (unlikely (ctx_terminated)) {
         errno = ETERM;
-        EXIT_MUTEX ();
         return -1;
     }
 
     //  First, check whether specific socket type overloads the option.
     int rc = xsetsockopt (option_, optval_, optvallen_);
     if (rc == 0 || errno != EINVAL) {
-        EXIT_MUTEX ();
         return rc;
     }
 
@@ -364,64 +355,55 @@ int zmq::socket_base_t::setsockopt (int option_, const void *optval_,
     rc = options.setsockopt (option_, optval_, optvallen_);
     update_pipe_options(option_);
 
-    EXIT_MUTEX ();
     return rc;
 }
 
 int zmq::socket_base_t::getsockopt (int option_, void *optval_,
     size_t *optvallen_)
 {
-    ENTER_MUTEX ();
+    scoped_optional_lock_t sync_lock(thread_safe ? &sync : 0);
 
     if (unlikely (ctx_terminated)) {
         errno = ETERM;
-        EXIT_MUTEX ();
         return -1;
     }
 
     if (option_ == ZMQ_RCVMORE) {
         if (*optvallen_ < sizeof (int)) {
             errno = EINVAL;
-            EXIT_MUTEX ();
             return -1;
         }
         memset(optval_, 0, *optvallen_);
         *((int*) optval_) = rcvmore ? 1 : 0;
         *optvallen_ = sizeof (int);
-        EXIT_MUTEX ();
         return 0;
     }
 
     if (option_ == ZMQ_FD) {
         if (*optvallen_ < sizeof (fd_t)) {
             errno = EINVAL;
-            EXIT_MUTEX ();
             return -1;
         }
 
         if (thread_safe) {
             // thread safe socket doesn't provide file descriptor
             errno = EINVAL;
-            EXIT_MUTEX ();
             return -1;
         }
 
         *((fd_t*)optval_) = ((mailbox_t*)mailbox)->get_fd();
         *optvallen_ = sizeof(fd_t);
 
-        EXIT_MUTEX ();
         return 0;
     }
 
     if (option_ == ZMQ_EVENTS) {
         if (*optvallen_ < sizeof (int)) {
             errno = EINVAL;
-            EXIT_MUTEX ();
             return -1;
         }
         int rc = process_commands (0, false);
         if (rc != 0 && (errno == EINTR || errno == ETERM)) {
-            EXIT_MUTEX ();
             return -1;
         }
         errno_assert (rc == 0);
@@ -431,108 +413,94 @@ int zmq::socket_base_t::getsockopt (int option_, void *optval_,
         if (has_in ())
             *((int*) optval_) |= ZMQ_POLLIN;
         *optvallen_ = sizeof (int);
-        EXIT_MUTEX ();
         return 0;
     }
 
     if (option_ == ZMQ_LAST_ENDPOINT) {
         if (*optvallen_ < last_endpoint.size () + 1) {
             errno = EINVAL;
-            EXIT_MUTEX ();
             return -1;
         }
         strncpy(static_cast <char *> (optval_), last_endpoint.c_str(), last_endpoint.size() + 1);
         *optvallen_ = last_endpoint.size () + 1;
-        EXIT_MUTEX ();
         return 0;
     }
 
     if (option_ == ZMQ_THREAD_SAFE) {
         if (*optvallen_ < sizeof (int)) {
             errno = EINVAL;
-            EXIT_MUTEX ();
             return -1;
         }
         memset(optval_, 0, *optvallen_);
         *((int*) optval_) = thread_safe	? 1 : 0;
         *optvallen_ = sizeof (int);
-        EXIT_MUTEX ();
         return 0;
     }
 
     int rc = options.getsockopt (option_, optval_, optvallen_);
-    EXIT_MUTEX ();
     return rc;
 }
 
 int zmq::socket_base_t::join (const char* group_)
 {
-    ENTER_MUTEX ();
+    scoped_optional_lock_t sync_lock(thread_safe ? &sync : 0);
 
     int rc = xjoin (group_);
 
-    EXIT_MUTEX();
 
     return rc;
 }
 
 int zmq::socket_base_t::leave (const char* group_)
 {
-    ENTER_MUTEX ();
+    scoped_optional_lock_t sync_lock(thread_safe ? &sync : 0);
 
     int rc = xleave (group_);
 
-    EXIT_MUTEX();
 
     return rc;
 }
 
 int zmq::socket_base_t::add_signaler(signaler_t *s_)
 {
-    ENTER_MUTEX ();
+    scoped_optional_lock_t sync_lock(thread_safe ? &sync : 0);
 
     if (!thread_safe) {
         errno = EINVAL;
-        EXIT_MUTEX ();
         return -1;
     }
 
     ((mailbox_safe_t*)mailbox)->add_signaler(s_);
 
-    EXIT_MUTEX ();
     return 0;
 }
 
 int zmq::socket_base_t::remove_signaler(signaler_t *s_)
 {
-    ENTER_MUTEX ();
+    scoped_optional_lock_t sync_lock(thread_safe ? &sync : 0);
 
     if (!thread_safe) {
         errno = EINVAL;
-        EXIT_MUTEX ();
         return -1;
     }
 
     ((mailbox_safe_t*)mailbox)->remove_signaler(s_);
 
-    EXIT_MUTEX ();
     return 0;
 }
 
 int zmq::socket_base_t::bind (const char *addr_)
 {
-    ENTER_MUTEX ();
+    scoped_optional_lock_t sync_lock(thread_safe ? &sync : 0);
 
     if (unlikely (ctx_terminated)) {
         errno = ETERM;
-        EXIT_MUTEX ();
         return -1;
     }
 
     //  Process pending commands, if any.
     int rc = process_commands (0, false);
     if (unlikely (rc != 0)) {
-        EXIT_MUTEX ();
         return -1;
     }
 
@@ -540,7 +508,6 @@ int zmq::socket_base_t::bind (const char *addr_)
     std::string protocol;
     std::string address;
     if (parse_uri (addr_, protocol, address) || check_protocol (protocol)) {
-        EXIT_MUTEX ();
         return -1;
     }
 
@@ -552,14 +519,12 @@ int zmq::socket_base_t::bind (const char *addr_)
             last_endpoint.assign (addr_);
             options.connected = true;
         }
-        EXIT_MUTEX ();
         return rc;
     }
 
     if (protocol == "pgm" || protocol == "epgm" || protocol == "norm") {
         //  For convenience's sake, bind can be used interchangeable with
         //  connect for PGM, EPGM, NORM transports.
-        EXIT_MUTEX ();
         rc = connect (addr_);
         if (rc != -1)
             options.connected = true;
@@ -569,7 +534,6 @@ int zmq::socket_base_t::bind (const char *addr_)
     if (protocol == "udp") {
         if (!(options.type == ZMQ_DGRAM || options.type == ZMQ_DISH)) {
             errno = ENOCOMPATPROTO;
-            EXIT_MUTEX ();
             return -1;
         }
 
@@ -577,7 +541,6 @@ int zmq::socket_base_t::bind (const char *addr_)
         io_thread_t *io_thread = choose_io_thread (options.affinity);
         if (!io_thread) {
             errno = EMTHREAD;
-            EXIT_MUTEX ();
             return -1;
         }
 
@@ -589,7 +552,6 @@ int zmq::socket_base_t::bind (const char *addr_)
         rc = paddr->resolved.udp_addr->resolve (address.c_str(), true);
         if (rc != 0) {
             LIBZMQ_DELETE(paddr);
-            EXIT_MUTEX ();
             return -1;
         }
 
@@ -620,7 +582,6 @@ int zmq::socket_base_t::bind (const char *addr_)
 
         add_endpoint (addr_, (own_t *) session, newpipe);
 
-        EXIT_MUTEX ();
         return 0;
     }
 
@@ -629,7 +590,6 @@ int zmq::socket_base_t::bind (const char *addr_)
     io_thread_t *io_thread = choose_io_thread (options.affinity);
     if (!io_thread) {
         errno = EMTHREAD;
-        EXIT_MUTEX ();
         return -1;
     }
 
@@ -641,7 +601,6 @@ int zmq::socket_base_t::bind (const char *addr_)
         if (rc != 0) {
             LIBZMQ_DELETE(listener);
             event_bind_failed (address, zmq_errno());
-            EXIT_MUTEX ();
             return -1;
         }
 
@@ -650,7 +609,6 @@ int zmq::socket_base_t::bind (const char *addr_)
 
         add_endpoint (last_endpoint.c_str (), (own_t *) listener, NULL);
         options.connected = true;
-        EXIT_MUTEX ();
         return 0;
     }
 
@@ -663,7 +621,6 @@ int zmq::socket_base_t::bind (const char *addr_)
         if (rc != 0) {
             LIBZMQ_DELETE(listener);
             event_bind_failed (address, zmq_errno());
-            EXIT_MUTEX ();
             return -1;
         }
 
@@ -672,7 +629,6 @@ int zmq::socket_base_t::bind (const char *addr_)
 
         add_endpoint (last_endpoint.c_str (), (own_t *) listener, NULL);
         options.connected = true;
-        EXIT_MUTEX ();
         return 0;
     }
 #endif
@@ -685,7 +641,6 @@ int zmq::socket_base_t::bind (const char *addr_)
          if (rc != 0) {
              LIBZMQ_DELETE(listener);
              event_bind_failed (address, zmq_errno());
-             EXIT_MUTEX ();
              return -1;
          }
 
@@ -694,7 +649,6 @@ int zmq::socket_base_t::bind (const char *addr_)
 
         add_endpoint (addr_, (own_t *) listener, NULL);
         options.connected = true;
-        EXIT_MUTEX ();
         return 0;
     }
 #endif
@@ -707,7 +661,6 @@ int zmq::socket_base_t::bind (const char *addr_)
         if (rc != 0) {
             LIBZMQ_DELETE(listener);
             event_bind_failed (address, zmq_errno ());
-            EXIT_MUTEX ();
             return -1;
         }
 
@@ -715,30 +668,26 @@ int zmq::socket_base_t::bind (const char *addr_)
 
         add_endpoint (last_endpoint.c_str(), (own_t *) listener, NULL);
         options.connected = true;
-        EXIT_MUTEX ();
         return 0;
     }
 #endif
 
-    EXIT_MUTEX ();
     zmq_assert (false);
     return -1;
 }
 
 int zmq::socket_base_t::connect (const char *addr_)
 {
-    ENTER_MUTEX ();
+    scoped_optional_lock_t sync_lock(thread_safe ? &sync : 0);
 
     if (unlikely (ctx_terminated)) {
         errno = ETERM;
-        EXIT_MUTEX ();
         return -1;
     }
 
     //  Process pending commands, if any.
     int rc = process_commands (0, false);
     if (unlikely (rc != 0)) {
-        EXIT_MUTEX ();
         return -1;
     }
 
@@ -746,7 +695,6 @@ int zmq::socket_base_t::connect (const char *addr_)
     std::string protocol;
     std::string address;
     if (parse_uri (addr_, protocol, address) || check_protocol (protocol)) {
-        EXIT_MUTEX ();
         return -1;
     }
 
@@ -852,7 +800,6 @@ int zmq::socket_base_t::connect (const char *addr_)
         inprocs.insert (inprocs_t::value_type (std::string (addr_), new_pipes [0]));
 
         options.connected = true;
-        EXIT_MUTEX ();
         return 0;
     }
     bool is_single_connect = (options.type == ZMQ_DEALER ||
@@ -864,7 +811,6 @@ int zmq::socket_base_t::connect (const char *addr_)
             // There is no valid use for multiple connects for SUB-PUB nor
             // DEALER-ROUTER nor REQ-REP. Multiple connects produces
             // nonsensical results.
-            EXIT_MUTEX ();
             return 0;
         }
     }
@@ -873,7 +819,6 @@ int zmq::socket_base_t::connect (const char *addr_)
     io_thread_t *io_thread = choose_io_thread (options.affinity);
     if (!io_thread) {
         errno = EMTHREAD;
-        EXIT_MUTEX ();
         return -1;
     }
 
@@ -918,7 +863,6 @@ int zmq::socket_base_t::connect (const char *addr_)
         if (rc == -1) {
             errno = EINVAL;
             LIBZMQ_DELETE(paddr);
-            EXIT_MUTEX ();
             return -1;
         }
         //  Defer resolution until a socket is opened
@@ -932,7 +876,6 @@ int zmq::socket_base_t::connect (const char *addr_)
         int rc = paddr->resolved.ipc_addr->resolve (address.c_str ());
         if (rc != 0) {
             LIBZMQ_DELETE(paddr);
-            EXIT_MUTEX ();
             return -1;
         }
     }
@@ -942,7 +885,6 @@ if (protocol  == "udp") {
     if (options.type != ZMQ_RADIO) {
         errno = ENOCOMPATPROTO;
         LIBZMQ_DELETE(paddr);
-        EXIT_MUTEX ();
         return -1;
     }
 
@@ -951,7 +893,6 @@ if (protocol  == "udp") {
     rc = paddr->resolved.udp_addr->resolve (address.c_str(), false);
     if (rc != 0) {
         LIBZMQ_DELETE(paddr);
-        EXIT_MUTEX ();
         return -1;
     }
 }
@@ -966,7 +907,6 @@ if (protocol  == "udp") {
         if (res != NULL)
             pgm_freeaddrinfo (res);
         if (rc != 0 || port_number == 0) {
-          EXIT_MUTEX ();
           return -1;
         }
     }
@@ -979,7 +919,6 @@ if (protocol  == "udp") {
         int rc = paddr->resolved.tipc_addr->resolve (address.c_str());
         if (rc != 0) {
             LIBZMQ_DELETE(paddr);
-            EXIT_MUTEX ();
             return -1;
         }
     }
@@ -992,7 +931,6 @@ if (protocol  == "udp") {
         int rc = paddr->resolved.vmci_addr->resolve (address.c_str ());
         if (rc != 0) {
             LIBZMQ_DELETE(paddr);
-            EXIT_MUTEX ();
             return -1;
         }
     }
@@ -1038,7 +976,6 @@ if (protocol  == "udp") {
     paddr->to_string (last_endpoint);
 
     add_endpoint (addr_, (own_t *) session, newpipe);
-    EXIT_MUTEX ();
     return 0;
 }
 
@@ -1051,19 +988,17 @@ void zmq::socket_base_t::add_endpoint (const char *addr_, own_t *endpoint_, pipe
 
 int zmq::socket_base_t::term_endpoint (const char *addr_)
 {
-    ENTER_MUTEX ();
+    scoped_optional_lock_t sync_lock(thread_safe ? &sync : 0);
 
     //  Check whether the library haven't been shut down yet.
     if (unlikely (ctx_terminated)) {
         errno = ETERM;
-        EXIT_MUTEX ();
         return -1;
     }
 
     //  Check whether endpoint address passed to the function is valid.
     if (unlikely (!addr_)) {
         errno = EINVAL;
-        EXIT_MUTEX ();
         return -1;
     }
 
@@ -1071,7 +1006,6 @@ int zmq::socket_base_t::term_endpoint (const char *addr_)
     //  (from launch_child() for example) we're asked to terminate now.
     int rc = process_commands (0, false);
     if (unlikely(rc != 0)) {
-        EXIT_MUTEX ();
         return -1;
     }
 
@@ -1079,27 +1013,23 @@ int zmq::socket_base_t::term_endpoint (const char *addr_)
     std::string protocol;
     std::string address;
     if (parse_uri(addr_, protocol, address) || check_protocol(protocol)) {
-        EXIT_MUTEX ();
         return -1;
     }
 
     // Disconnect an inproc socket
     if (protocol == "inproc") {
         if (unregister_endpoint (std::string(addr_), this) == 0) {
-            EXIT_MUTEX ();
             return 0;
         }
         std::pair <inprocs_t::iterator, inprocs_t::iterator> range = inprocs.equal_range (std::string (addr_));
         if (range.first == range.second) {
             errno = ENOENT;
-            EXIT_MUTEX ();
             return -1;
         }
 
         for (inprocs_t::iterator it = range.first; it != range.second; ++it)
             it->second->terminate (true);
         inprocs.erase (range.first, range.second);
-        EXIT_MUTEX ();
         return 0;
     }
 
@@ -1137,7 +1067,6 @@ int zmq::socket_base_t::term_endpoint (const char *addr_)
     range = endpoints.equal_range (resolved_addr);
     if (range.first == range.second) {
         errno = ENOENT;
-        EXIT_MUTEX ();
         return -1;
     }
 
@@ -1148,32 +1077,28 @@ int zmq::socket_base_t::term_endpoint (const char *addr_)
         term_child (it->second.first);
     }
     endpoints.erase (range.first, range.second);
-    EXIT_MUTEX ();
     return 0;
 }
 
 int zmq::socket_base_t::send (msg_t *msg_, int flags_)
 {
-    ENTER_MUTEX ();
+    scoped_optional_lock_t sync_lock(thread_safe ? &sync : 0);
 
     //  Check whether the library haven't been shut down yet.
     if (unlikely (ctx_terminated)) {
         errno = ETERM;
-        EXIT_MUTEX ();
         return -1;
     }
 
     //  Check whether message passed to the function is valid.
     if (unlikely (!msg_ || !msg_->check ())) {
         errno = EFAULT;
-        EXIT_MUTEX ();
         return -1;
     }
 
     //  Process pending commands, if any.
     int rc = process_commands (0, true);
     if (unlikely (rc != 0)) {
-        EXIT_MUTEX ();
         return -1;
     }
 
@@ -1189,18 +1114,15 @@ int zmq::socket_base_t::send (msg_t *msg_, int flags_)
     //  Try to send the message using method in each socket class
     rc = xsend (msg_);
     if (rc == 0) {
-        EXIT_MUTEX ();
         return 0;
     }
     if (unlikely (errno != EAGAIN)) {
-        EXIT_MUTEX ();
         return -1;
     }
 
     //  In case of non-blocking send we'll simply propagate
     //  the error - including EAGAIN - up the stack.
     if (flags_ & ZMQ_DONTWAIT || options.sndtimeo == 0) {
-        EXIT_MUTEX ();
         return -1;
     }
 
@@ -1214,45 +1136,39 @@ int zmq::socket_base_t::send (msg_t *msg_, int flags_)
     //  If timeout is reached in the meantime, return EAGAIN.
     while (true) {
         if (unlikely (process_commands (timeout, false) != 0)) {
-            EXIT_MUTEX ();
             return -1;
         }
         rc = xsend (msg_);
         if (rc == 0)
             break;
         if (unlikely (errno != EAGAIN)) {
-            EXIT_MUTEX ();
             return -1;
         }
         if (timeout > 0) {
             timeout = (int) (end - clock.now_ms ());
             if (timeout <= 0) {
                 errno = EAGAIN;
-                EXIT_MUTEX ();
                 return -1;
             }
         }
     }
 
-    EXIT_MUTEX ();
     return 0;
 }
 
 int zmq::socket_base_t::recv (msg_t *msg_, int flags_)
 {
-    ENTER_MUTEX ();
+    scoped_optional_lock_t sync_lock(thread_safe ? &sync : 0);
 
     //  Check whether the library haven't been shut down yet.
     if (unlikely (ctx_terminated)) {
         errno = ETERM;
-        EXIT_MUTEX ();
         return -1;
     }
 
     //  Check whether message passed to the function is valid.
     if (unlikely (!msg_ || !msg_->check ())) {
         errno = EFAULT;
-        EXIT_MUTEX ();
         return -1;
     }
 
@@ -1266,7 +1182,6 @@ int zmq::socket_base_t::recv (msg_t *msg_, int flags_)
     //  ticks is more efficient than doing RDTSC all the time.
     if (++ticks == inbound_poll_rate) {
         if (unlikely (process_commands (0, false) != 0)) {
-            EXIT_MUTEX ();
             return -1;
         }
         ticks = 0;
@@ -1275,14 +1190,12 @@ int zmq::socket_base_t::recv (msg_t *msg_, int flags_)
     //  Get the message.
     int rc = xrecv (msg_);
     if (unlikely (rc != 0 && errno != EAGAIN)) {
-        EXIT_MUTEX ();
         return -1;
     }
 
     //  If we have the message, return immediately.
     if (rc == 0) {
         extract_flags (msg_);
-        EXIT_MUTEX ();
         return 0;
     }
 
@@ -1292,19 +1205,16 @@ int zmq::socket_base_t::recv (msg_t *msg_, int flags_)
     //  If it's not, return EAGAIN.
     if (flags_ & ZMQ_DONTWAIT || options.rcvtimeo == 0) {
         if (unlikely (process_commands (0, false) != 0)) {
-            EXIT_MUTEX ();
             return -1;
         }
         ticks = 0;
 
         rc = xrecv (msg_);
         if (rc < 0) {
-            EXIT_MUTEX ();
             return rc;
         }
         extract_flags (msg_);
 
-        EXIT_MUTEX ();
         return 0;
     }
 
@@ -1318,7 +1228,6 @@ int zmq::socket_base_t::recv (msg_t *msg_, int flags_)
     bool block = (ticks != 0);
     while (true) {
         if (unlikely (process_commands (block ? timeout : 0, false) != 0)) {
-            EXIT_MUTEX ();
             return -1;
         }
         rc = xrecv (msg_);
@@ -1327,7 +1236,6 @@ int zmq::socket_base_t::recv (msg_t *msg_, int flags_)
             break;
         }
         if (unlikely (errno != EAGAIN)) {
-            EXIT_MUTEX ();
             return -1;
         }
         block = true;
@@ -1335,20 +1243,18 @@ int zmq::socket_base_t::recv (msg_t *msg_, int flags_)
             timeout = (int) (end - clock.now_ms ());
             if (timeout <= 0) {
                 errno = EAGAIN;
-                EXIT_MUTEX ();
                 return -1;
             }
         }
     }
 
     extract_flags (msg_);
-    EXIT_MUTEX ();
     return 0;
 }
 
 int zmq::socket_base_t::close ()
 {
-    ENTER_MUTEX ();
+    scoped_optional_lock_t sync_lock(thread_safe ? &sync : 0);
 
     //  Remove all existing signalers for thread safe sockets
     if (thread_safe)
@@ -1357,7 +1263,6 @@ int zmq::socket_base_t::close ()
     //  Mark the socket as dead
     tag = 0xdeadbeef;
 
-    EXIT_MUTEX ();
 
     //  Transfer the ownership of the socket from this application thread
     //  to the reaper thread which will take care of the rest of shutdown
@@ -1387,7 +1292,7 @@ void zmq::socket_base_t::start_reaping (poller_t *poller_)
     if (!thread_safe)
         fd = ((mailbox_t*)mailbox)->get_fd();
     else {
-        ENTER_MUTEX ();
+        scoped_optional_lock_t sync_lock(thread_safe ? &sync : 0);
 
         reaper_signaler =  new signaler_t();
 
@@ -1398,7 +1303,6 @@ void zmq::socket_base_t::start_reaping (poller_t *poller_)
         //  Send a signal to make sure reaper handle existing commands
         reaper_signaler->send();
 
-        EXIT_MUTEX ();
     }
 
     handle = poller->add_fd (fd, this);
@@ -1581,14 +1485,13 @@ void zmq::socket_base_t::in_event ()
     //  of the reaper thread. Process any commands from other threads/sockets
     //  that may be available at the moment. Ultimately, the socket will
     //  be destroyed.
-    ENTER_MUTEX ();
+    scoped_optional_lock_t sync_lock(thread_safe ? &sync : 0);
 
     //  If the socket is thread safe we need to unsignal the reaper signaler
     if (thread_safe)
         reaper_signaler->recv();
 
     process_commands (0, false);
-    EXIT_MUTEX();
     check_destroy();
 }