diff --git a/src/c/symbols_list.h b/src/c/symbols_list.h
index 820df6de5..94425ad29 100755
--- a/src/c/symbols_list.h
+++ b/src/c/symbols_list.h
@@ -1564,6 +1564,7 @@ cl_symbols[] = {
 {MP_ "INTERRUPT-PROCESS", MP_ORDINARY, IF_MP(mp_interrupt_process), 2, OBJNULL},
 {MP_ "+LOAD-COMPILE-LOCK+", MP_CONSTANT, NULL, -1, OBJNULL},
 {MP_ "WITH-LOCK", MP_CONSTANT, NULL, -1, OBJNULL},
+{MP_ "WITH-RWLOCK", MP_CONSTANT, NULL, -1, OBJNULL},
 {MP_ "BLOCK-SIGNALS", MP_ORDINARY, IF_MP(mp_block_signals), 0, OBJNULL},
 {MP_ "RESTORE-SIGNALS", MP_ORDINARY, IF_MP(mp_restore_signals), 1, OBJNULL},
 {MP_ "PROCESS-SUSPEND", MP_ORDINARY, IF_MP(mp_process_suspend), 1, OBJNULL},
@@ -1584,6 +1585,7 @@ cl_symbols[] = {
 {MP_ "MAKE-SEMAPHORE", MP_ORDINARY, IF_MP(mp_make_semaphore), -1, OBJNULL},
 {MP_ "SIGNAL-SEMAPHORE", MP_ORDINARY, IF_MP(mp_signal_semaphore), -1, OBJNULL},
 {MP_ "WAIT-ON-SEMAPHORE", MP_ORDINARY, IF_MP(mp_wait_on_semaphore), 1, OBJNULL},
+{MP_ "TRY-GET-SEMAPHORE", MP_ORDINARY, IF_MP(mp_try_get_semaphore), 1, OBJNULL},
 {MP_ "SEMAPHORE-COUNT", MP_ORDINARY, IF_MP(mp_semaphore_count), 1, OBJNULL},
 {MP_ "SEMAPHORE-NAME", MP_ORDINARY, IF_MP(mp_semaphore_name), 1, OBJNULL},
 {MP_ "SEMAPHORE-WAIT-COUNT", MP_ORDINARY, IF_MP(mp_semaphore_wait_count), 1, OBJNULL},
@@ -1607,7 +1609,9 @@ cl_symbols[] = {
 {MP_ "MAILBOX-COUNT", MP_ORDINARY, IF_MP(mp_mailbox_count), 1, OBJNULL},
 {MP_ "MAILBOX-EMPTY-P", MP_ORDINARY, IF_MP(mp_mailbox_empty_p), 1, OBJNULL},
 {MP_ "MAILBOX-READ", MP_ORDINARY, IF_MP(mp_mailbox_read), 1, OBJNULL},
+{MP_ "MAILBOX-TRY-READ", MP_ORDINARY, IF_MP(mp_mailbox_try_read), 1, OBJNULL},
 {MP_ "MAILBOX-SEND", MP_ORDINARY, IF_MP(mp_mailbox_send), 2, OBJNULL},
+{MP_ "MAILBOX-TRY-SEND", MP_ORDINARY, IF_MP(mp_mailbox_try_send), 2, OBJNULL},
 /* #endif defined(ECL_THREADS) */
 
 {SYS_ "WHILE", SI_ORDINARY, NULL, -1, OBJNULL},
diff --git a/src/c/symbols_list2.h b/src/c/symbols_list2.h
index 8a9e314ca..ea645173a 100644
--- a/src/c/symbols_list2.h
+++ b/src/c/symbols_list2.h
@@ -1564,6 +1564,7 @@ cl_symbols[] = {
 {MP_ "INTERRUPT-PROCESS",IF_MP("mp_interrupt_process")},
 {MP_ "+LOAD-COMPILE-LOCK+",NULL},
 {MP_ "WITH-LOCK",NULL},
+{MP_ "WITH-RWLOCK",NULL},
 {MP_ "BLOCK-SIGNALS",IF_MP("mp_block_signals")},
 {MP_ "RESTORE-SIGNALS",IF_MP("mp_restore_signals")},
 {MP_ "PROCESS-SUSPEND",IF_MP("mp_process_suspend")},
@@ -1584,6 +1585,7 @@ cl_symbols[] = {
 {MP_ "MAKE-SEMAPHORE",IF_MP("mp_make_semaphore")},
 {MP_ "SIGNAL-SEMAPHORE",IF_MP("mp_signal_semaphore")},
 {MP_ "WAIT-ON-SEMAPHORE",IF_MP("mp_wait_on_semaphore")},
+{MP_ "TRY-GET-SEMAPHORE",IF_MP("mp_try_get_semaphore")},
 {MP_ "SEMAPHORE-COUNT",IF_MP("mp_semaphore_count")},
 {MP_ "SEMAPHORE-NAME",IF_MP("mp_semaphore_name")},
 {MP_ "SEMAPHORE-WAIT-COUNT",IF_MP("mp_semaphore_wait_count")},
@@ -1607,7 +1609,9 @@ cl_symbols[] = {
 {MP_ "MAILBOX-COUNT",IF_MP("mp_mailbox_count")},
 {MP_ "MAILBOX-EMPTY-P",IF_MP("mp_mailbox_empty_p")},
 {MP_ "MAILBOX-READ",IF_MP("mp_mailbox_read")},
+{MP_ "MAILBOX-TRY-READ",IF_MP("mp_mailbox_try_read")},
 {MP_ "MAILBOX-SEND",IF_MP("mp_mailbox_send")},
+{MP_ "MAILBOX-TRY-SEND",IF_MP("mp_mailbox_try_send")},
 /* #endif defined(ECL_THREADS) */
 
 {SYS_ "WHILE",NULL},
diff --git a/src/c/threads/mailbox.d b/src/c/threads/mailbox.d
index fdda559df..615c2ec34 100755
--- a/src/c/threads/mailbox.d
+++ b/src/c/threads/mailbox.d
@@ -107,6 +107,25 @@ mp_mailbox_read(cl_object mailbox)
         ecl_return1(env, output);
 }
 
+cl_object
+mp_mailbox_try_read(cl_object mailbox)
+{
+        cl_env_ptr env = ecl_process_env();
+        cl_fixnum ndx;
+        cl_object output;
+        unlikely_if (ecl_t_of(mailbox) != t_mailbox) {
+                FEerror_not_a_mailbox(mailbox);
+        }
+        output = mp_try_get_semaphore(mailbox->mailbox.reader_semaphore);
+        if (output != ECL_NIL) {
+                ndx = AO_fetch_and_add1((AO_t*)&mailbox->mailbox.read_pointer) &
+                        mailbox->mailbox.mask;
+                output = mailbox->mailbox.data->vector.self.t[ndx];
+                mp_signal_semaphore(1, mailbox->mailbox.writer_semaphore);
+        }
+        ecl_return1(env, output);
+}
+
 cl_object
 mp_mailbox_send(cl_object mailbox, cl_object msg)
 {
@@ -124,3 +143,24 @@ mp_mailbox_send(cl_object mailbox, cl_object msg)
         mp_signal_semaphore(1, mailbox->mailbox.reader_semaphore);
         ecl_return0(env);
 }
+
+cl_object
+mp_mailbox_try_send(cl_object mailbox, cl_object msg)
+{
+        cl_env_ptr env = ecl_process_env();
+        cl_object output;
+        cl_fixnum ndx;
+        unlikely_if (ecl_t_of(mailbox) != t_mailbox) {
+                FEerror_not_a_mailbox(mailbox);
+        }
+        output = mp_try_get_semaphore(mailbox->mailbox.writer_semaphore);
+        if (output != ECL_NIL) {
+                output = msg;
+                ndx = AO_fetch_and_add1((AO_t*)&mailbox->mailbox.write_pointer) &
+                        mailbox->mailbox.mask;
+                mailbox->mailbox.data->vector.self.t[ndx] = msg;
+                mp_signal_semaphore(1, mailbox->mailbox.reader_semaphore);
+        }
+        ecl_return1(env, output);
+}
+
diff --git a/src/c/threads/semaphore.d b/src/c/threads/semaphore.d
index ccd4bf21b..04d7850dc 100644
--- a/src/c/threads/semaphore.d
+++ b/src/c/threads/semaphore.d
@@ -127,3 +127,15 @@ mp_wait_on_semaphore(cl_object semaphore)
         }
         ecl_return1(env, output);
 }
+
+cl_object
+mp_try_get_semaphore(cl_object semaphore)
+{
+        cl_env_ptr env = ecl_process_env();
+        cl_object output;
+        unlikely_if (ecl_t_of(semaphore) != t_semaphore) {
+                FEerror_not_a_semaphore(semaphore);
+        }
+        ecl_return1(env, get_semaphore_inner(env, semaphore));
+}
+
diff --git a/src/h/external.h b/src/h/external.h
index 2e05ede5c..20bf4692a 100755
--- a/src/h/external.h
+++ b/src/h/external.h
@@ -1734,6 +1734,7 @@ extern ECL_API cl_object mp_semaphore_count(cl_object);
 extern ECL_API cl_object mp_semaphore_name(cl_object);
 extern ECL_API cl_object mp_semaphore_wait_count(cl_object);
 extern ECL_API cl_object mp_wait_on_semaphore(cl_object);
+extern ECL_API cl_object mp_try_get_semaphore(cl_object);
 extern ECL_API cl_object mp_signal_semaphore _ECL_ARGS((cl_narg, cl_object, ...));
 extern ECL_API cl_object ecl_make_semaphore(cl_object name, cl_fixnum count);
 
@@ -1754,7 +1755,9 @@ extern ECL_API cl_object mp_mailbox_name(cl_object mailbox);
 extern ECL_API cl_object mp_mailbox_count(cl_object mailbox);
 extern ECL_API cl_object mp_mailbox_empty_p(cl_object);
 extern ECL_API cl_object mp_mailbox_read(cl_object mailbox);
+extern ECL_API cl_object mp_mailbox_try_read(cl_object mailbox);
 extern ECL_API cl_object mp_mailbox_send(cl_object mailbox, cl_object msg);
+extern ECL_API cl_object mp_mailbox_try_send(cl_object mailbox, cl_object msg);
 
 /* threads/atomic.c */
 
diff --git a/src/lsp/mp.lsp b/src/lsp/mp.lsp
index 56c4770fe..c0f30f8fa 100644
--- a/src/lsp/mp.lsp
+++ b/src/lsp/mp.lsp
@@ -133,3 +133,18 @@ by ALLOW-WITH-INTERRUPTS."
                               (> (the fixnum (mp:lock-count ,lock))
                                  (the fixnum ,count))))
                  (mp::giveup-lock ,lock))))))))
+
+#+ecl-read-write-lock
+(defmacro with-rwlock ((lock op) &body body)
+  (assert (member op '(:read :write) :test #'eq))
+  (let ((s-lock (gensym)))
+    `(let ((,s-lock ,lock))
+       (,(if (eq :read op)
+             'mp:get-rwlock-read
+             'mp:get-rwlock-write) ,s-lock t)
+       (unwind-protect
+            (progn
+              ,@body)
+         (,(if (eq :read op)
+               'mp:giveup-rwlock-read
+               'mp:giveup-rwlock-write) ,s-lock)))))
diff --git a/src/lsp/top.lsp b/src/lsp/top.lsp
index f7eb627b6..867b2a2bc 100644
--- a/src/lsp/top.lsp
+++ b/src/lsp/top.lsp
@@ -41,6 +41,7 @@
 (defparameter *last-error* nil)
 
 (defparameter *break-message* nil)
+(defparameter *break-condition* nil)
 
 (defparameter *break-readtable* nil)
 (defparameter *tpl-level* -1)                   ; nesting level of top-level loops
@@ -773,7 +774,7 @@ Use special code 0 to cancel this operation.")
 
 (defun tpl-disassemble-command ()
   (let*((*print-level* 2)
-        (*print-length* 4)
+        (*print-length* 16)
         (*print-pretty* t)
         (*print-escape* nil)
         (*print-readably* nil)
@@ -1014,7 +1015,7 @@ Use special code 0 to cancel this operation.")
 
 (defun tpl-variables-command (&optional no-values)
   (let*((*print-level* 2)
-        (*print-length* 4)
+        (*print-length* 16)
         (*print-pretty* t)
         (*print-escape* nil)
         (*print-readably* nil))
@@ -1060,7 +1061,7 @@ Use special code 0 to cancel this operation.")
          (last (frs-bds (1+ *frs-top*)))
          (fi *frs-base*)
          (*print-level* 2)
-         (*print-length* 4)
+         (*print-length* 16)
          (*print-pretty* t))
         ((> bi last) (values))
       (do ()
@@ -1134,7 +1135,7 @@ Use special code 0 to cancel this operation.")
       ((= k 0) (values))
       (let*((j (or (sch-frs-base *frs-base* i) (1+ *frs-top*)))
             (*print-level* 2)
-            (*print-length* 4)
+            (*print-length* 16)
             (*print-pretty* t))
         (do () ((or (> j *frs-top*) (> (frs-ihs j) i)))
             (print-frs j)
@@ -1429,10 +1430,11 @@ package."
            (*print-readably* nil)
            (*print-pretty* nil)
            (*print-circle* t)
-           (*print-length* 2)
+           (*print-length* 16)
            (*readtable* (or *break-readtable* *readtable*))
            (*break-message* (format nil "~&Condition of type: ~A~%~A~%"
                                     (type-of condition) condition))
+           (*break-condition* condition)
            (*break-level* (1+ *break-level*))
            (break-level *break-level*)
            (*break-env* nil))
diff --git a/src/new-cmp/cmpmain.lsp b/src/new-cmp/cmpmain.lsp
index dce4982ae..c9219d5c0 100644
--- a/src/new-cmp/cmpmain.lsp
+++ b/src/new-cmp/cmpmain.lsp
@@ -19,6 +19,10 @@
 (defmacro with-lock ((lock) &body body)
   `(progn ,@body))
 
+#-ecl-read-write-lock
+(defmacro with-rwlock ((lock op) &body body)
+  `(progn ,@body))
+
 (defun safe-system (string)
   (cmpnote "Invoking external command:~%  ~A" string)
   (let ((result (si:system string)))