diff --git a/src/ast/rewriter/th_rewriter.cpp b/src/ast/rewriter/th_rewriter.cpp
index e2aca747b..a91a681d9 100644
--- a/src/ast/rewriter/th_rewriter.cpp
+++ b/src/ast/rewriter/th_rewriter.cpp
@@ -734,11 +734,8 @@ unsigned th_rewriter::get_num_steps() const {
 
 void th_rewriter::cleanup() {
     ast_manager & m = m_imp->m();
-    #pragma omp critical (th_rewriter)
-    {
-        dealloc(m_imp);
-        m_imp = alloc(imp, m, m_params);
-    }
+    dealloc(m_imp);
+    m_imp = alloc(imp, m, m_params);    
 }
 
 void th_rewriter::reset() {
diff --git a/src/math/euclid/euclidean_solver.cpp b/src/math/euclid/euclidean_solver.cpp
index 25419d7d1..af11d4304 100644
--- a/src/math/euclid/euclidean_solver.cpp
+++ b/src/math/euclid/euclidean_solver.cpp
@@ -796,12 +796,9 @@ void euclidean_solver::reset() {
     numeral_manager * m = m_imp->m_manager;
     bool owns_m         = m_imp->m_owns_m;
     m_imp->m_owns_m     = false;
-    #pragma omp critical (euclidean_solver)
-    {
-        dealloc(m_imp);
-        m_imp = alloc(imp, m);
-        m_imp->m_owns_m = owns_m;
-    }
+    dealloc(m_imp);
+    m_imp = alloc(imp, m);
+    m_imp->m_owns_m = owns_m;    
 }
 
 euclidean_solver::var euclidean_solver::mk_var() {
diff --git a/src/math/subpaving/tactic/subpaving_tactic.cpp b/src/math/subpaving/tactic/subpaving_tactic.cpp
index a0f84c04c..27e096777 100644
--- a/src/math/subpaving/tactic/subpaving_tactic.cpp
+++ b/src/math/subpaving/tactic/subpaving_tactic.cpp
@@ -261,17 +261,8 @@ public:
     
     virtual void cleanup() {
         ast_manager & m = m_imp->m();
-        imp * d = m_imp;
-        #pragma omp critical (tactic_cancel)
-        {
-            d = m_imp;
-        }
-        dealloc(d);
-        d = alloc(imp, m, m_params);
-        #pragma omp critical (tactic_cancel) 
-        {
-            m_imp = d;
-        }
+        dealloc(m_imp);
+        m_imp = alloc(imp, m, m_params);
     }
 
 };
diff --git a/src/muz/fp/horn_tactic.cpp b/src/muz/fp/horn_tactic.cpp
index c1a74f5c7..b3e7eeb67 100644
--- a/src/muz/fp/horn_tactic.cpp
+++ b/src/muz/fp/horn_tactic.cpp
@@ -403,18 +403,10 @@ public:
     
     virtual void cleanup() {
         ast_manager & m = m_imp->m;
-        imp * d = m_imp;
-        d->collect_statistics(m_stats);
-        #pragma omp critical (tactic_cancel)
-        {
-            m_imp = 0;
-        }
-        dealloc(d);
-        d = alloc(imp, m_is_simplify, m, m_params);
-        #pragma omp critical (tactic_cancel)
-        {
-            m_imp = d;
-        }
+        m_imp->collect_statistics(m_stats);
+        dealloc(m_imp);
+        m_imp = alloc(imp, m_is_simplify, m, m_params);
+        
     }
     
 
diff --git a/src/nlsat/tactic/goal2nlsat.cpp b/src/nlsat/tactic/goal2nlsat.cpp
index 031dc5ff5..00114cf05 100644
--- a/src/nlsat/tactic/goal2nlsat.cpp
+++ b/src/nlsat/tactic/goal2nlsat.cpp
@@ -262,17 +262,11 @@ struct goal2nlsat::imp {
 struct goal2nlsat::scoped_set_imp {
     goal2nlsat & m_owner; 
     scoped_set_imp(goal2nlsat & o, imp & i):m_owner(o) {
-        #pragma omp critical (tactic_cancel)
-        {
-            m_owner.m_imp = &i;
-        }
+        m_owner.m_imp = &i;        
     }
     
     ~scoped_set_imp() {
-        #pragma omp critical (tactic_cancel)
-        {
-            m_owner.m_imp = 0;
-        }
+        m_owner.m_imp = 0;        
     }
 };
 
diff --git a/src/nlsat/tactic/nlsat_tactic.cpp b/src/nlsat/tactic/nlsat_tactic.cpp
index 8ab6ed83f..94c57e16d 100644
--- a/src/nlsat/tactic/nlsat_tactic.cpp
+++ b/src/nlsat/tactic/nlsat_tactic.cpp
@@ -175,18 +175,12 @@ class nlsat_tactic : public tactic {
     struct scoped_set_imp {
         nlsat_tactic & m_owner; 
         scoped_set_imp(nlsat_tactic & o, imp & i):m_owner(o) {
-            #pragma omp critical (tactic_cancel)
-            {
-                m_owner.m_imp = &i;
-            }
+            m_owner.m_imp = &i;            
         }
 
         ~scoped_set_imp() {
             m_owner.m_imp->m_solver.collect_statistics(m_owner.m_stats);
-            #pragma omp critical (tactic_cancel)
-            {
-                m_owner.m_imp = 0;
-            }
+            m_owner.m_imp = 0;
         }
     };
 
diff --git a/src/qe/qe_lite.cpp b/src/qe/qe_lite.cpp
index c3fed3676..4364d4a21 100644
--- a/src/qe/qe_lite.cpp
+++ b/src/qe/qe_lite.cpp
@@ -2569,17 +2569,8 @@ public:
     
     virtual void cleanup() {
         ast_manager & m = m_imp->m;
-        imp * d = m_imp;
-        #pragma omp critical (tactic_cancel)
-        {
-            m_imp = 0;
-        }
-        dealloc(d);
-        d = alloc(imp, m, m_params);
-        #pragma omp critical (tactic_cancel)
-        {
-            m_imp = d;
-        }
+        dealloc(m_imp);
+        m_imp = alloc(imp, m, m_params);
     }
     
 };
diff --git a/src/qe/qe_tactic.cpp b/src/qe/qe_tactic.cpp
index 0c3a79f68..d72727250 100644
--- a/src/qe/qe_tactic.cpp
+++ b/src/qe/qe_tactic.cpp
@@ -121,17 +121,8 @@ public:
     
     virtual void cleanup() {
         ast_manager & m = m_imp->m;
-        imp * d = m_imp;
-        #pragma omp critical (tactic_cancel)
-        {
-            m_imp = 0;
-        }
-        dealloc(d);
-        d = alloc(imp, m, m_params);
-        #pragma omp critical (tactic_cancel)
-        {
-            m_imp = d;
-        }
+        dealloc(m_imp);
+        m_imp = alloc(imp, m, m_params);
     }
     
 };
diff --git a/src/sat/tactic/goal2sat.cpp b/src/sat/tactic/goal2sat.cpp
index 4e649862a..fbf34e741 100644
--- a/src/sat/tactic/goal2sat.cpp
+++ b/src/sat/tactic/goal2sat.cpp
@@ -485,16 +485,10 @@ void goal2sat::collect_param_descrs(param_descrs & r) {
 struct goal2sat::scoped_set_imp {
     goal2sat * m_owner; 
     scoped_set_imp(goal2sat * o, goal2sat::imp * i):m_owner(o) {
-        #pragma omp critical (goal2sat)
-        {
-            m_owner->m_imp = i;
-        }
+        m_owner->m_imp = i;        
     }
     ~scoped_set_imp() {
-        #pragma omp critical (goal2sat)
-        {
-            m_owner->m_imp = 0;
-        }
+        m_owner->m_imp = 0;        
     }
 };
 
@@ -732,16 +726,10 @@ void sat2goal::collect_param_descrs(param_descrs & r) {
 struct sat2goal::scoped_set_imp {
     sat2goal * m_owner; 
     scoped_set_imp(sat2goal * o, sat2goal::imp * i):m_owner(o) {
-        #pragma omp critical (sat2goal)
-        {
-            m_owner->m_imp = i;
-        }
+        m_owner->m_imp = i;        
     }
     ~scoped_set_imp() {
-        #pragma omp critical (sat2goal)
-        {
-            m_owner->m_imp = 0;
-        }
+        m_owner->m_imp = 0;        
     }
 };
 
diff --git a/src/sat/tactic/sat_tactic.cpp b/src/sat/tactic/sat_tactic.cpp
index d6ec1dff0..da513d97b 100644
--- a/src/sat/tactic/sat_tactic.cpp
+++ b/src/sat/tactic/sat_tactic.cpp
@@ -145,17 +145,11 @@ class sat_tactic : public tactic {
         sat_tactic * m_owner; 
 
         scoped_set_imp(sat_tactic * o, imp * i):m_owner(o) {
-            #pragma omp critical (sat_tactic)
-            {
-                m_owner->m_imp = i;
-            }
+            m_owner->m_imp = i;            
         }
         
         ~scoped_set_imp() {
-            #pragma omp critical (sat_tactic)
-            {
-                m_owner->m_imp = 0;
-            }
+            m_owner->m_imp = 0;        
         }
     };
 
diff --git a/src/smt/tactic/smt_tactic.cpp b/src/smt/tactic/smt_tactic.cpp
index 4ae31d778..63ca3e4e3 100644
--- a/src/smt/tactic/smt_tactic.cpp
+++ b/src/smt/tactic/smt_tactic.cpp
@@ -167,18 +167,14 @@ public:
             if (o.m_callback) {
                 new_ctx->set_progress_callback(o.m_callback);
             }
-            #pragma omp critical (as_st_solver) 
-            {
-                o.m_ctx = new_ctx;
-            }
+            o.m_ctx = new_ctx;
+            
         }
 
         ~scoped_init_ctx() {
             smt::kernel * d = m_owner.m_ctx;
-            #pragma omp critical (as_st_cancel)
-            {
-                m_owner.m_ctx = 0;
-            }
+            m_owner.m_ctx = 0;
+            
             if (d)
                 dealloc(d);
         }
diff --git a/src/tactic/arith/diff_neq_tactic.cpp b/src/tactic/arith/diff_neq_tactic.cpp
index 7f03c05b2..5cc021f6f 100644
--- a/src/tactic/arith/diff_neq_tactic.cpp
+++ b/src/tactic/arith/diff_neq_tactic.cpp
@@ -394,10 +394,7 @@ public:
     virtual void cleanup() {
         imp * d = alloc(imp, m_imp->m, m_params);
         d->m_num_conflicts = m_imp->m_num_conflicts;
-        #pragma omp critical (tactic_cancel)
-        {
-            std::swap(d, m_imp);
-        }
+        std::swap(d, m_imp);        
         dealloc(d);
     }
 
diff --git a/src/tactic/arith/factor_tactic.cpp b/src/tactic/arith/factor_tactic.cpp
index f00ff81c9..70bff2610 100644
--- a/src/tactic/arith/factor_tactic.cpp
+++ b/src/tactic/arith/factor_tactic.cpp
@@ -330,10 +330,7 @@ public:
 
     virtual void cleanup() {
         imp * d = alloc(imp, m_imp->m, m_params);
-        #pragma omp critical (tactic_cancel)
-        {
-            std::swap(d, m_imp);
-        }
+        std::swap(d, m_imp);        
         dealloc(d);
     }
 
diff --git a/src/tactic/arith/fix_dl_var_tactic.cpp b/src/tactic/arith/fix_dl_var_tactic.cpp
index d9a3150fc..1a9a18c44 100644
--- a/src/tactic/arith/fix_dl_var_tactic.cpp
+++ b/src/tactic/arith/fix_dl_var_tactic.cpp
@@ -335,10 +335,7 @@ public:
     
     virtual void cleanup() {
         imp * d = alloc(imp, m_imp->m, m_params);
-        #pragma omp critical (tactic_cancel)
-        {
-            std::swap(d, m_imp);
-        }
+        std::swap(d, m_imp);        
         dealloc(d);
     }
 };
diff --git a/src/tactic/arith/fm_tactic.cpp b/src/tactic/arith/fm_tactic.cpp
index 722b3db30..4674459dd 100644
--- a/src/tactic/arith/fm_tactic.cpp
+++ b/src/tactic/arith/fm_tactic.cpp
@@ -1669,10 +1669,7 @@ public:
 
     virtual void cleanup() {
         imp * d = alloc(imp, m_imp->m, m_params);
-        #pragma omp critical (tactic_cancel)
-        {
-            std::swap(d, m_imp);
-        }
+        std::swap(d, m_imp);        
         dealloc(d);
     }
 
diff --git a/src/tactic/arith/lia2card_tactic.cpp b/src/tactic/arith/lia2card_tactic.cpp
index 7dda928d3..f36a93e6d 100644
--- a/src/tactic/arith/lia2card_tactic.cpp
+++ b/src/tactic/arith/lia2card_tactic.cpp
@@ -400,11 +400,8 @@ public:
     virtual void cleanup() {        
         expr_set* d = alloc(expr_set);
         ptr_vector<expr>* todo = alloc(ptr_vector<expr>);
-        #pragma omp critical (tactic_cancel)
-        {
-            std::swap(m_01s, d);
-            std::swap(m_todo, todo);
-        }
+        std::swap(m_01s, d);
+        std::swap(m_todo, todo);        
         dealloc(d);
         dealloc(todo);
     }
diff --git a/src/tactic/arith/lia2pb_tactic.cpp b/src/tactic/arith/lia2pb_tactic.cpp
index 3a745fae3..1ad662218 100644
--- a/src/tactic/arith/lia2pb_tactic.cpp
+++ b/src/tactic/arith/lia2pb_tactic.cpp
@@ -346,10 +346,7 @@ public:
     
     virtual void cleanup() {
         imp * d = alloc(imp, m_imp->m, m_params);
-        #pragma omp critical (tactic_cancel)
-        {
-            std::swap(d, m_imp);
-        }
+        std::swap(d, m_imp);        
         dealloc(d);
     }
 
diff --git a/src/tactic/arith/nla2bv_tactic.cpp b/src/tactic/arith/nla2bv_tactic.cpp
index bd5af58f2..085cb4de3 100644
--- a/src/tactic/arith/nla2bv_tactic.cpp
+++ b/src/tactic/arith/nla2bv_tactic.cpp
@@ -404,17 +404,11 @@ class nla2bv_tactic : public tactic {
         nla2bv_tactic & m_owner; 
         scoped_set_imp(nla2bv_tactic & o, imp & i):
             m_owner(o) {
-            #pragma omp critical (tactic_cancel)
-            {
-                m_owner.m_imp = &i;
-            }
+            m_owner.m_imp = &i;            
         }
 
         ~scoped_set_imp() {
-            #pragma omp critical (tactic_cancel)
-            {
-                m_owner.m_imp = 0;
-            }
+            m_owner.m_imp = 0;            
         }
     };
     
diff --git a/src/tactic/arith/normalize_bounds_tactic.cpp b/src/tactic/arith/normalize_bounds_tactic.cpp
index 729d9986e..b3ec505ea 100644
--- a/src/tactic/arith/normalize_bounds_tactic.cpp
+++ b/src/tactic/arith/normalize_bounds_tactic.cpp
@@ -189,10 +189,7 @@ public:
     virtual void cleanup() {
         ast_manager & m = m_imp->m;
         imp * d = alloc(imp, m, m_params);
-        #pragma omp critical (tactic_cancel)
-        {
-            std::swap(d, m_imp);
-        }
+        std::swap(d, m_imp);        
         dealloc(d);
     }
 };
diff --git a/src/tactic/arith/pb2bv_tactic.cpp b/src/tactic/arith/pb2bv_tactic.cpp
index ebb82fbc1..4c3790af3 100644
--- a/src/tactic/arith/pb2bv_tactic.cpp
+++ b/src/tactic/arith/pb2bv_tactic.cpp
@@ -1004,10 +1004,7 @@ public:
     virtual void cleanup() {
         ast_manager & m = m_imp->m;
         imp * d = alloc(imp, m, m_params);
-        #pragma omp critical (tactic_cancel)
-        {
-            std::swap(d, m_imp);
-        }
+        std::swap(d, m_imp);        
         dealloc(d);
     }
 
diff --git a/src/tactic/arith/propagate_ineqs_tactic.cpp b/src/tactic/arith/propagate_ineqs_tactic.cpp
index cec110fd1..1a3447f38 100644
--- a/src/tactic/arith/propagate_ineqs_tactic.cpp
+++ b/src/tactic/arith/propagate_ineqs_tactic.cpp
@@ -544,9 +544,6 @@ void propagate_ineqs_tactic::operator()(goal_ref const & g,
  
 void propagate_ineqs_tactic::cleanup() {
     imp * d = alloc(imp, m_imp->m, m_params);
-    #pragma omp critical (tactic_cancel)
-    {
-        std::swap(d, m_imp);
-    }
+    std::swap(d, m_imp);    
     dealloc(d);
 }
diff --git a/src/tactic/arith/recover_01_tactic.cpp b/src/tactic/arith/recover_01_tactic.cpp
index 4e7f8f342..393d30b58 100644
--- a/src/tactic/arith/recover_01_tactic.cpp
+++ b/src/tactic/arith/recover_01_tactic.cpp
@@ -423,10 +423,7 @@ public:
     
     virtual void cleanup() {
         imp * d = alloc(imp, m_imp->m, m_params);
-        #pragma omp critical (tactic_cancel)
-        {
-            std::swap(d, m_imp);
-        }
+        std::swap(d, m_imp);        
         dealloc(d);
     }
 };
diff --git a/src/tactic/bv/bit_blaster_tactic.cpp b/src/tactic/bv/bit_blaster_tactic.cpp
index 391057877..7e19585d9 100644
--- a/src/tactic/bv/bit_blaster_tactic.cpp
+++ b/src/tactic/bv/bit_blaster_tactic.cpp
@@ -149,10 +149,7 @@ public:
 
     virtual void cleanup() {
         imp * d = alloc(imp, m_imp->m(), m_rewriter, m_params);
-        #pragma omp critical (tactic_cancel)
-        {
-            std::swap(d, m_imp);
-        }
+        std::swap(d, m_imp);        
         dealloc(d);
     }
     
diff --git a/src/tactic/bv/bv1_blaster_tactic.cpp b/src/tactic/bv/bv1_blaster_tactic.cpp
index 55709b01e..2e142cb13 100644
--- a/src/tactic/bv/bv1_blaster_tactic.cpp
+++ b/src/tactic/bv/bv1_blaster_tactic.cpp
@@ -464,10 +464,7 @@ public:
     
     virtual void cleanup() {
         imp * d = alloc(imp, m_imp->m(), m_params);
-        #pragma omp critical (tactic_cancel)
-        {
-            std::swap(d, m_imp);
-        }
+        std::swap(d, m_imp);        
         dealloc(d);
     }
     
diff --git a/src/tactic/bv/bv_size_reduction_tactic.cpp b/src/tactic/bv/bv_size_reduction_tactic.cpp
index 0bc41ad11..8c93aeb90 100644
--- a/src/tactic/bv/bv_size_reduction_tactic.cpp
+++ b/src/tactic/bv/bv_size_reduction_tactic.cpp
@@ -400,10 +400,7 @@ void bv_size_reduction_tactic::operator()(goal_ref const & g,
  
 void bv_size_reduction_tactic::cleanup() {
     imp * d = alloc(imp, m_imp->m);
-    #pragma omp critical (tactic_cancel)
-    {
-        std::swap(d, m_imp);
-    }
+    std::swap(d, m_imp);    
     dealloc(d);
 }
 
diff --git a/src/tactic/bv/bvarray2uf_tactic.cpp b/src/tactic/bv/bvarray2uf_tactic.cpp
index d5c381ad7..50063b8a5 100644
--- a/src/tactic/bv/bvarray2uf_tactic.cpp
+++ b/src/tactic/bv/bvarray2uf_tactic.cpp
@@ -143,10 +143,7 @@ public:
     virtual void cleanup() {
         ast_manager & m = m_imp->m();
         imp * d = alloc(imp, m, m_params);
-    #pragma omp critical (tactic_cancel)
-        {
-            std::swap(d, m_imp);
-        }
+        std::swap(d, m_imp);        
         dealloc(d);
     }
 
diff --git a/src/tactic/bv/elim_small_bv_tactic.cpp b/src/tactic/bv/elim_small_bv_tactic.cpp
index f93102645..7a83ee403 100644
--- a/src/tactic/bv/elim_small_bv_tactic.cpp
+++ b/src/tactic/bv/elim_small_bv_tactic.cpp
@@ -307,10 +307,7 @@ public:
     virtual void cleanup() {
         ast_manager & m = m_imp->m;
         imp * d = alloc(imp, m, m_params);
-#pragma omp critical (tactic_cancel)
-        {
-            std::swap(d, m_imp);
-        }
+        std::swap(d, m_imp);    
         dealloc(d);
     }
 
diff --git a/src/tactic/bv/max_bv_sharing_tactic.cpp b/src/tactic/bv/max_bv_sharing_tactic.cpp
index 5e25b719d..675f26ace 100644
--- a/src/tactic/bv/max_bv_sharing_tactic.cpp
+++ b/src/tactic/bv/max_bv_sharing_tactic.cpp
@@ -308,10 +308,7 @@ public:
     
     virtual void cleanup() {
         imp * d = alloc(imp, m_imp->m(), m_params);
-        #pragma omp critical (tactic_cancel)
-        {
-            std::swap(d, m_imp);
-        }
+        std::swap(d, m_imp);        
         dealloc(d);
     }
 };
diff --git a/src/tactic/core/blast_term_ite_tactic.cpp b/src/tactic/core/blast_term_ite_tactic.cpp
index 4251a10bd..03b8e6cfa 100644
--- a/src/tactic/core/blast_term_ite_tactic.cpp
+++ b/src/tactic/core/blast_term_ite_tactic.cpp
@@ -183,16 +183,11 @@ public:
     virtual void cleanup() {
         ast_manager & m = m_imp->m;
         imp * d = m_imp;
-        #pragma omp critical (tactic_cancel)
-        {
-            m_imp = 0;
-        }
+        m_imp = 0;
+        
         dealloc(d);
         d = alloc(imp, m, m_params);
-        #pragma omp critical (tactic_cancel)
-        {
-            m_imp = d;
-        }
+        m_imp = d;        
     }
 
     static void blast_term_ite(expr_ref& fml) {
diff --git a/src/tactic/core/cofactor_elim_term_ite.cpp b/src/tactic/core/cofactor_elim_term_ite.cpp
index 305b59ab4..43e3559ba 100644
--- a/src/tactic/core/cofactor_elim_term_ite.cpp
+++ b/src/tactic/core/cofactor_elim_term_ite.cpp
@@ -697,10 +697,7 @@ void cofactor_elim_term_ite::operator()(expr * t, expr_ref & r) {
 void cofactor_elim_term_ite::cleanup() {
     ast_manager & m = m_imp->m;    
     imp * d = alloc(imp, m, m_params);
-    #pragma omp critical (tactic_cancel)
-    {
-        std::swap(d, m_imp);
-    }
+    std::swap(d, m_imp);    
     dealloc(d);
 }
 
diff --git a/src/tactic/core/ctx_simplify_tactic.cpp b/src/tactic/core/ctx_simplify_tactic.cpp
index 27354a7e0..987d5a48d 100644
--- a/src/tactic/core/ctx_simplify_tactic.cpp
+++ b/src/tactic/core/ctx_simplify_tactic.cpp
@@ -540,10 +540,7 @@ void ctx_simplify_tactic::operator()(goal_ref const & in,
 void ctx_simplify_tactic::cleanup() {
     ast_manager & m   = m_imp->m;
     imp * d = alloc(imp, m, m_params);
-    #pragma omp critical (tactic_cancel)
-    {
-        std::swap(d, m_imp);
-    }
+    std::swap(d, m_imp);    
     dealloc(d);
 }
 
diff --git a/src/tactic/core/der_tactic.cpp b/src/tactic/core/der_tactic.cpp
index b136adef7..ece1ec42f 100644
--- a/src/tactic/core/der_tactic.cpp
+++ b/src/tactic/core/der_tactic.cpp
@@ -87,10 +87,7 @@ public:
     virtual void cleanup() {
         ast_manager & m = m_imp->m();
         imp * d = alloc(imp, m);
-        #pragma omp critical (tactic_cancel)
-        {
-            std::swap(d, m_imp);
-        }
+        std::swap(d, m_imp);        
         dealloc(d);
     }
     
diff --git a/src/tactic/core/distribute_forall_tactic.cpp b/src/tactic/core/distribute_forall_tactic.cpp
index 074dfdb54..769f415f2 100644
--- a/src/tactic/core/distribute_forall_tactic.cpp
+++ b/src/tactic/core/distribute_forall_tactic.cpp
@@ -108,10 +108,7 @@ public:
         ast_manager & m = g->m();
         bool produce_proofs = g->proofs_enabled();
         rw r(m, produce_proofs);
-        #pragma omp critical (tactic_cancel)
-        {
-            m_rw = &r;
-        }
+        m_rw = &r;        
         mc = 0; pc = 0; core = 0; result.reset();
         tactic_report report("distribute-forall", *g);
         
@@ -134,10 +131,7 @@ public:
         result.push_back(g.get());
         TRACE("distribute-forall", g->display(tout););
         SASSERT(g->is_well_sorted());
-        #pragma omp critical (tactic_cancel)
-        {
-            m_rw = 0;
-        }
+        m_rw = 0;        
     }
 
     virtual void cleanup() {}
diff --git a/src/tactic/core/elim_term_ite_tactic.cpp b/src/tactic/core/elim_term_ite_tactic.cpp
index 1e7f91c1c..6cc989d0f 100644
--- a/src/tactic/core/elim_term_ite_tactic.cpp
+++ b/src/tactic/core/elim_term_ite_tactic.cpp
@@ -172,10 +172,7 @@ public:
     virtual void cleanup() {
         ast_manager & m = m_imp->m;
         imp * d = alloc(imp, m, m_params);
-        #pragma omp critical (tactic_cancel)
-        {
-            std::swap(d, m_imp);
-        }
+        std::swap(d, m_imp);        
         dealloc(d);
     }
 
diff --git a/src/tactic/core/elim_uncnstr_tactic.cpp b/src/tactic/core/elim_uncnstr_tactic.cpp
index 6ccbe2a56..538797ddf 100644
--- a/src/tactic/core/elim_uncnstr_tactic.cpp
+++ b/src/tactic/core/elim_uncnstr_tactic.cpp
@@ -895,10 +895,7 @@ class elim_uncnstr_tactic : public tactic {
         }
         
         void init_rw(bool produce_proofs) {
-            #pragma omp critical (tactic_cancel)
-            {
-                m_rw = alloc(rw, m(), produce_proofs, m_vars, m_mc.get(), m_max_memory, m_max_steps);
-            }
+            m_rw = alloc(rw, m(), produce_proofs, m_vars, m_mc.get(), m_max_memory, m_max_steps);            
         }
 
         virtual void operator()(goal_ref const & g, 
@@ -968,10 +965,7 @@ class elim_uncnstr_tactic : public tactic {
                         }
                     }
                     m_mc = 0;
-                    #pragma omp critical (tactic_cancel)
-                    {
-                        m_rw  = 0;
-                    }
+                    m_rw  = 0;                    
                     TRACE("elim_uncnstr", if (mc) mc->display(tout););
                     result.push_back(g.get());
                     g->inc_depth();
@@ -1034,10 +1028,7 @@ public:
         unsigned num_elim_apps = get_num_elim_apps();
         ast_manager & m = m_imp->m_manager;        
         imp * d = alloc(imp, m, m_params);
-        #pragma omp critical (tactic_cancel)
-        {
-            std::swap(d, m_imp);
-        }
+        std::swap(d, m_imp);        
         dealloc(d);
         m_imp->m_num_elim_apps = num_elim_apps;
     }
diff --git a/src/tactic/core/nnf_tactic.cpp b/src/tactic/core/nnf_tactic.cpp
index f921330e3..f9244f8e7 100644
--- a/src/tactic/core/nnf_tactic.cpp
+++ b/src/tactic/core/nnf_tactic.cpp
@@ -29,17 +29,11 @@ class nnf_tactic : public tactic {
         
         set_nnf(nnf_tactic & owner, nnf & n):
             m_owner(owner) {
-            #pragma omp critical (nnf_tactic)
-            {
-                m_owner.m_nnf = &n;
-            }
+            m_owner.m_nnf = &n;            
         }
         
         ~set_nnf() {
-            #pragma omp critical (nnf_tactic)
-            {
-                m_owner.m_nnf = 0;
-            }
+            m_owner.m_nnf = 0;            
         }
     };
 public:
diff --git a/src/tactic/core/occf_tactic.cpp b/src/tactic/core/occf_tactic.cpp
index 0914bfdef..c080ee915 100644
--- a/src/tactic/core/occf_tactic.cpp
+++ b/src/tactic/core/occf_tactic.cpp
@@ -220,10 +220,7 @@ public:
     
     virtual void cleanup() {
         imp * d = alloc(imp, m_imp->m);
-        #pragma omp critical (tactic_cancel)
-        {
-            std::swap(d, m_imp);
-        }
+        std::swap(d, m_imp);        
         dealloc(d);
     }
     
diff --git a/src/tactic/core/propagate_values_tactic.cpp b/src/tactic/core/propagate_values_tactic.cpp
index 30f63942a..d266548d5 100644
--- a/src/tactic/core/propagate_values_tactic.cpp
+++ b/src/tactic/core/propagate_values_tactic.cpp
@@ -257,10 +257,7 @@ public:
     virtual void cleanup() {
         ast_manager & m = m_imp->m();
         imp * d = alloc(imp, m, m_params);
-        #pragma omp critical (tactic_cancel)
-        {
-            std::swap(d, m_imp);
-        }
+        std::swap(d, m_imp);        
         dealloc(d);
     }
     
diff --git a/src/tactic/core/reduce_args_tactic.cpp b/src/tactic/core/reduce_args_tactic.cpp
index 3990b9a1f..121dbeef3 100644
--- a/src/tactic/core/reduce_args_tactic.cpp
+++ b/src/tactic/core/reduce_args_tactic.cpp
@@ -532,10 +532,7 @@ void reduce_args_tactic::operator()(goal_ref const & g,
 void reduce_args_tactic::cleanup() {
     ast_manager & m   = m_imp->m();    
     imp * d = alloc(imp, m);
-    #pragma omp critical (tactic_cancel)
-    {
-        std::swap(d, m_imp);
-    }
+    std::swap(d, m_imp);    
     dealloc(d);
 }
 
diff --git a/src/tactic/core/simplify_tactic.cpp b/src/tactic/core/simplify_tactic.cpp
index 8f4b9fb9e..be89d356a 100644
--- a/src/tactic/core/simplify_tactic.cpp
+++ b/src/tactic/core/simplify_tactic.cpp
@@ -112,10 +112,7 @@ void simplify_tactic::operator()(goal_ref const & in,
 void simplify_tactic::cleanup() {
     ast_manager & m = m_imp->m();
     imp * d = alloc(imp, m, m_params);
-    #pragma omp critical (tactic_cancel)
-    {
-        std::swap(d, m_imp);
-    }
+    std::swap(d, m_imp);    
     dealloc(d);
 }
 
diff --git a/src/tactic/core/solve_eqs_tactic.cpp b/src/tactic/core/solve_eqs_tactic.cpp
index bf1364314..01c4bc10b 100644
--- a/src/tactic/core/solve_eqs_tactic.cpp
+++ b/src/tactic/core/solve_eqs_tactic.cpp
@@ -751,10 +751,7 @@ public:
 
         imp * d = alloc(imp, m, m_params, r, owner);
         d->m_num_eliminated_vars = num_elim_vars;
-        #pragma omp critical (tactic_cancel)
-        {
-            std::swap(d, m_imp);
-        }
+        std::swap(d, m_imp);        
         dealloc(d);
     }
 
diff --git a/src/tactic/core/tseitin_cnf_tactic.cpp b/src/tactic/core/tseitin_cnf_tactic.cpp
index ffdb36ac3..03e9ce7fa 100644
--- a/src/tactic/core/tseitin_cnf_tactic.cpp
+++ b/src/tactic/core/tseitin_cnf_tactic.cpp
@@ -896,10 +896,7 @@ public:
         ast_manager & m = m_imp->m;
         imp * d = alloc(imp, m, m_params);
         d->m_num_aux_vars = m_imp->m_num_aux_vars;
-        #pragma omp critical (tactic_cancel)
-        {
-            std::swap(d, m_imp);
-        }
+        std::swap(d, m_imp);        
         dealloc(d);
     }
 
diff --git a/src/tactic/fpa/fpa2bv_tactic.cpp b/src/tactic/fpa/fpa2bv_tactic.cpp
index e067a6ade..cfedb66d7 100644
--- a/src/tactic/fpa/fpa2bv_tactic.cpp
+++ b/src/tactic/fpa/fpa2bv_tactic.cpp
@@ -155,10 +155,7 @@ public:
 
     virtual void cleanup() {
         imp * d = alloc(imp, m_imp->m, m_params);
-        #pragma omp critical (tactic_cancel)
-        {
-            std::swap(d, m_imp);
-        }
+        std::swap(d, m_imp);        
         dealloc(d);
     }
 
diff --git a/src/tactic/sls/sls_tactic.cpp b/src/tactic/sls/sls_tactic.cpp
index 38101c2fe..4e49e0d76 100644
--- a/src/tactic/sls/sls_tactic.cpp
+++ b/src/tactic/sls/sls_tactic.cpp
@@ -80,10 +80,7 @@ public:
 
     virtual void cleanup() {        
         sls_engine * d = alloc(sls_engine, m, m_params);
-        #pragma omp critical (tactic_cancel)
-        {
-            std::swap(d, m_engine);
-        }
+        std::swap(d, m_engine);            
         dealloc(d);
     }
     
diff --git a/src/tactic/tactical.cpp b/src/tactic/tactical.cpp
index 14ceacdbf..d79bd2ed1 100644
--- a/src/tactic/tactical.cpp
+++ b/src/tactic/tactical.cpp
@@ -461,10 +461,21 @@ enum par_exception_kind {
 };
 
 class par_tactical : public or_else_tactical {
+
+    struct scoped_limits {
+        reslimit&  m_limit;
+        unsigned   m_sz;
+        scoped_limits(reslimit& lim): m_limit(lim), m_sz(0) {}
+        ~scoped_limits() { for (unsigned i = 0; i < m_sz; ++i) m_limit.pop_child(); }
+        void push_child(reslimit* lim) { m_limit.push_child(lim); ++m_sz; }
+    };
+
 public:
     par_tactical(unsigned num, tactic * const * ts):or_else_tactical(num, ts) {}
     virtual ~par_tactical() {}
 
+    
+
     virtual void operator()(goal_ref const & in, 
                             goal_ref_buffer & result, 
                             model_converter_ref & mc, 
@@ -485,6 +496,7 @@ public:
         ast_manager & m = in->m();
         
         scoped_ptr_vector<ast_manager> managers;
+        scoped_limits scl(m.limit());
         goal_ref_vector                in_copies;
         tactic_ref_vector              ts;
         unsigned sz = m_ts.size();
@@ -494,6 +506,7 @@ public:
             ast_translation translator(m, *new_m);
             in_copies.push_back(in->translate(translator));
             ts.push_back(m_ts.get(i)->translate(*new_m));
+            scl.push_child(&new_m->limit());
         }
 
         unsigned finished_id       = UINT_MAX;
diff --git a/src/tactic/ufbv/macro_finder_tactic.cpp b/src/tactic/ufbv/macro_finder_tactic.cpp
index c14521bf4..e31682cd0 100644
--- a/src/tactic/ufbv/macro_finder_tactic.cpp
+++ b/src/tactic/ufbv/macro_finder_tactic.cpp
@@ -140,10 +140,7 @@ public:
     virtual void cleanup() {
         ast_manager & m = m_imp->m();
         imp * d = alloc(imp, m, m_params);
-        #pragma omp critical (tactic_cancel)
-        {
-            std::swap(d, m_imp);
-        }
+        std::swap(d, m_imp);        
         dealloc(d);
     }
 
diff --git a/src/tactic/ufbv/quasi_macros_tactic.cpp b/src/tactic/ufbv/quasi_macros_tactic.cpp
index 1647a97e2..5a5cba1f0 100644
--- a/src/tactic/ufbv/quasi_macros_tactic.cpp
+++ b/src/tactic/ufbv/quasi_macros_tactic.cpp
@@ -148,10 +148,7 @@ public:
     virtual void cleanup() {
         ast_manager & m = m_imp->m();
         imp * d = alloc(imp, m, m_params);
-        #pragma omp critical (tactic_cancel)
-        {
-            std::swap(d, m_imp);
-        }
+        std::swap(d, m_imp);        
         dealloc(d);
     }
 
diff --git a/src/tactic/ufbv/ufbv_rewriter_tactic.cpp b/src/tactic/ufbv/ufbv_rewriter_tactic.cpp
index ffe704354..5bcf5eae3 100644
--- a/src/tactic/ufbv/ufbv_rewriter_tactic.cpp
+++ b/src/tactic/ufbv/ufbv_rewriter_tactic.cpp
@@ -115,10 +115,7 @@ public:
     virtual void cleanup() {
         ast_manager & m = m_imp->m();
         imp * d = alloc(imp, m, m_params);
-        #pragma omp critical (tactic_cancel)
-        {
-            std::swap(d, m_imp);
-        }
+        std::swap(d, m_imp);        
         dealloc(d);
     }
 
diff --git a/src/util/rlimit.cpp b/src/util/rlimit.cpp
index 2a5746d0e..2ff079043 100644
--- a/src/util/rlimit.cpp
+++ b/src/util/rlimit.cpp
@@ -56,3 +56,16 @@ void reslimit::pop() {
     m_limits.pop_back();
     m_cancel = false;
 }
+
+void reslimit::cancel() { 
+    m_cancel = true; 
+    for (unsigned i = 0; i < m_children.size(); ++i) {
+        m_children[i]->cancel();
+    }
+}
+void reslimit::reset_cancel() { 
+    m_cancel = false; 
+    for (unsigned i = 0; i < m_children.size(); ++i) {
+        m_children[i]->reset_cancel();
+    }
+}
diff --git a/src/util/rlimit.h b/src/util/rlimit.h
index 10f58f5d5..9e7b4345a 100644
--- a/src/util/rlimit.h
+++ b/src/util/rlimit.h
@@ -26,19 +26,22 @@ class reslimit {
     uint64          m_count;
     uint64          m_limit;
     svector<uint64> m_limits;
-
+    ptr_vector<reslimit> m_children;
 public:    
     reslimit();
     void push(unsigned delta_limit);
     void pop();
+    void push_child(reslimit* r) { m_children.push_back(r); }
+    void pop_child() { m_children.pop_back(); }
+
     bool inc();
     bool inc(unsigned offset);
     uint64 count() const; 
 
 
     bool cancel_flag_set() { return m_cancel; }
-    void cancel() { m_cancel = true; }
-    void reset_cancel() { m_cancel = false; }
+    void cancel();
+    void reset_cancel();
 };
 
 class scoped_rlimit {