2 files changed, 335 insertions, 352 deletions

diff --git a/src/linda.cpp b/src/linda.cpp
index dc5864b..77dc4cb 100644
--- a/src/linda.cpp
+++ b/src/linda.cpp
@@ -1,5 +1,5 @@
 /*
- * LINDA.C                          Copyright (c) 2018, Benoit Germain
+ * LINDA.CPP                        Copyright (c) 2018-2024, Benoit Germain
  *
  * Linda deep userdata.
 */
@@ -30,20 +30,15 @@ THE SOFTWARE.
 ===============================================================================
 */
 
-#include <stdlib.h>
-#include <string.h>
-#include <assert.h>
-
-#include "threading.h"
 #include "compat.h"
-#include "tools.h"
-#include "universe.h"
-#include "keeper.h"
 #include "deep.h"
+#include "keeper.h"
 #include "lanes_private.h"
+#include "threading.h"
+#include "tools.h"
+#include "universe.h"
 
 #include <array>
-#include <bit>
 #include <variant>
 
 /*
@@ -166,11 +161,10 @@ static inline Linda* lua_toLinda(lua_State* L, int idx_)
 
 static void check_key_types(lua_State* L, int start_, int end_)
 {
-    int i;
-    for( i = start_; i <= end_; ++ i)
+    for (int i{ start_ }; i <= end_; ++i)
     {
-        int t = lua_type( L, i);
-        if( t == LUA_TBOOLEAN || t == LUA_TNUMBER || t == LUA_TSTRING || t == LUA_TLIGHTUSERDATA)
+        int const t{ lua_type(L, i) };
+        if (t == LUA_TBOOLEAN || t == LUA_TNUMBER || t == LUA_TSTRING || t == LUA_TLIGHTUSERDATA)
         {
             continue;
         }
@@ -185,26 +179,27 @@ LUAG_FUNC(linda_protected_call)
     Linda* const linda{ lua_toLinda<false>(L, 1) };
 
     // acquire the keeper
-    Keeper* K = keeper_acquire( linda->U->keepers, linda->hashSeed());
-    lua_State* KL = K ? K->L : nullptr;
-    if( KL == nullptr) return 0;
+    Keeper* const K{ keeper_acquire(linda->U->keepers, linda->hashSeed()) };
+    lua_State* const KL{ K ? K->L : nullptr };
+    if (KL == nullptr)
+        return 0;
 
     // retrieve the actual function to be called and move it before the arguments
-    lua_pushvalue( L, lua_upvalueindex( 1));
-    lua_insert( L, 1);
+    lua_pushvalue(L, lua_upvalueindex(1));
+    lua_insert(L, 1);
     // do a protected call
     int const rc{ lua_pcall(L, lua_gettop(L) - 1, LUA_MULTRET, 0) };
 
     // release the keeper
-    keeper_release( K);
+    keeper_release(K);
 
     // if there was an error, forward it
-    if( rc != LUA_OK)
+    if (rc != LUA_OK)
     {
         raise_lua_error(L);
     }
     // return whatever the actual operation provided
-    return lua_gettop( L);
+    return lua_gettop(L);
 }
 
 // #################################################################################################
@@ -218,7 +213,7 @@ LUAG_FUNC(linda_protected_call)
 *           'false' for timeout (only happens when the queue size is limited)
 *           nil, CANCEL_ERROR if cancelled
 */
-LUAG_FUNC( linda_send)
+LUAG_FUNC(linda_send)
 {
     Linda* const linda{ lua_toLinda<false>(L, 1) };
     bool ret{ false };
@@ -227,56 +222,57 @@ LUAG_FUNC( linda_send)
     time_d timeout = -1.0;
     int key_i = 2; // index of first key, if timeout not there
 
-    if( lua_type( L, 2) == LUA_TNUMBER) // we don't want to use lua_isnumber() because of autocoercion
+    if (lua_type(L, 2) == LUA_TNUMBER) // we don't want to use lua_isnumber() because of autocoercion
     {
-        timeout = SIGNAL_TIMEOUT_PREPARE( lua_tonumber( L, 2));
-        ++ key_i;
+        timeout = SIGNAL_TIMEOUT_PREPARE(lua_tonumber(L, 2));
+        ++key_i;
     }
-    else if( lua_isnil( L, 2)) // alternate explicit "no timeout" by passing nil before the key
+    else if (lua_isnil(L, 2)) // alternate explicit "no timeout" by passing nil before the key
     {
-        ++ key_i;
+        ++key_i;
     }
 
     bool const as_nil_sentinel{ NIL_SENTINEL.equals(L, key_i) }; // if not nullptr, send() will silently send a single nil if nothing is provided
-    if( as_nil_sentinel)
+    if (as_nil_sentinel)
     {
         // the real key to send data to is after the NIL_SENTINEL marker
-        ++ key_i;
+        ++key_i;
     }
 
     // make sure the key is of a valid type
-    check_key_types( L, key_i, key_i);
+    check_key_types(L, key_i, key_i);
 
-    STACK_GROW( L, 1);
+    STACK_GROW(L, 1);
 
     // make sure there is something to send
-    if( lua_gettop( L) == key_i)
+    if (lua_gettop(L) == key_i)
     {
-        if( as_nil_sentinel)
+        if (as_nil_sentinel)
         {
             // send a single nil if nothing is provided
             NIL_SENTINEL.push(L);
         }
         else
         {
-            return luaL_error( L, "no data to send");
+            return luaL_error(L, "no data to send");
         }
     }
 
     // convert nils to some special non-nil sentinel in sent values
-    keeper_toggle_nil_sentinels( L, key_i + 1, eLM_ToKeeper);
+    keeper_toggle_nil_sentinels(L, key_i + 1, eLM_ToKeeper);
 
     {
-        Lane* const s{ get_lane_from_registry(L) };
+        Lane* const lane{ get_lane_from_registry(L) };
         Keeper* const K{ which_keeper(linda->U->keepers, linda->hashSeed()) };
-        lua_State* KL = K ? K->L : nullptr;
-        if( KL == nullptr) return 0;
+        lua_State* const KL{ K ? K->L : nullptr };
+        if (KL == nullptr)
+            return 0;
         STACK_CHECK_START_REL(KL, 0);
-        for(bool try_again{ true };;)
+        for (bool try_again{ true };;)
         {
-            if( s != nullptr)
+            if (lane != nullptr)
             {
-                cancel = s->cancel_request;
+                cancel = lane->cancel_request;
             }
             cancel = (cancel != CancelRequest::None) ? cancel : linda->simulate_cancel;
             // if user wants to cancel, or looped because of a timeout, the call returns without sending anything
@@ -286,60 +282,60 @@ LUAG_FUNC( linda_send)
                 break;
             }
 
-            STACK_CHECK( KL, 0);
-            pushed = keeper_call( linda->U, KL, KEEPER_API( send), L, linda, key_i);
-            if( pushed < 0)
+            STACK_CHECK(KL, 0);
+            pushed = keeper_call(linda->U, KL, KEEPER_API(send), L, linda, key_i);
+            if (pushed < 0)
             {
                 break;
             }
-            ASSERT_L( pushed == 1);
+            ASSERT_L(pushed == 1);
 
-            ret = lua_toboolean( L, -1) ? true : false;
-            lua_pop( L, 1);
+            ret = lua_toboolean(L, -1) ? true : false;
+            lua_pop(L, 1);
 
-            if( ret)
+            if (ret)
             {
                 // Wake up ALL waiting threads
-                SIGNAL_ALL( &linda->write_happened);
+                SIGNAL_ALL(&linda->write_happened);
                 break;
             }
 
             // instant timout to bypass the wait syscall
-            if( timeout == 0.0)
+            if (timeout == 0.0)
             {
-                break;  /* no wait; instant timeout */
+                break; /* no wait; instant timeout */
             }
 
             // storage limit hit, wait until timeout or signalled that we should try again
             {
                 enum e_status prev_status = ERROR_ST; // prevent 'might be used uninitialized' warnings
-                if( s != nullptr)
+                if (lane != nullptr)
                 {
                     // change status of lane to "waiting"
-                    prev_status = s->status; // RUNNING, most likely
-                    ASSERT_L( prev_status == RUNNING); // but check, just in case
-                    s->status = WAITING;
-                    ASSERT_L( s->waiting_on == nullptr);
-                    s->waiting_on = &linda->read_happened;
+                    prev_status = lane->status; // RUNNING, most likely
+                    ASSERT_L(prev_status == RUNNING); // but check, just in case
+                    lane->status = WAITING;
+                    ASSERT_L(lane->waiting_on == nullptr);
+                    lane->waiting_on = &linda->read_happened;
                 }
                 // could not send because no room: wait until some data was read before trying again, or until timeout is reached
-                try_again = SIGNAL_WAIT( &linda->read_happened, &K->keeper_cs, timeout);
-                if( s != nullptr)
+                try_again = SIGNAL_WAIT(&linda->read_happened, &K->keeper_cs, timeout);
+                if (lane != nullptr)
                 {
-                    s->waiting_on = nullptr;
-                    s->status = prev_status;
+                    lane->waiting_on = nullptr;
+                    lane->status = prev_status;
                 }
             }
         }
-        STACK_CHECK( KL, 0);
+        STACK_CHECK(KL, 0);
     }
 
-    if( pushed < 0)
+    if (pushed < 0)
     {
-        return luaL_error( L, "tried to copy unsupported types");
+        return luaL_error(L, "tried to copy unsupported types");
     }
 
-    switch( cancel)
+    switch (cancel)
     {
         case CancelRequest::Soft:
         // if user wants to soft-cancel, the call returns lanes.cancel_error
@@ -351,7 +347,7 @@ LUAG_FUNC( linda_send)
         raise_cancel_error(L); // raises an error and doesn't return
 
         default:
-        lua_pushboolean( L, ret); // true (success) or false (timeout)
+        lua_pushboolean(L, ret); // true (success) or false (timeout)
         return 1;
     }
 }
@@ -369,132 +365,130 @@ LUAG_FUNC( linda_send)
  * returns the actual consumed values, or nil if there weren't enough values to consume
  *
  */
-#define BATCH_SENTINEL "270e6c9d-280f-4983-8fee-a7ecdda01475"
-LUAG_FUNC( linda_receive)
+// xxh64 of string "CANCEL_ERROR" generated at https://www.pelock.com/products/hash-calculator
+static constexpr UniqueKey BATCH_SENTINEL{ 0x2DDFEE0968C62AA7ull };
+LUAG_FUNC(linda_receive)
 {
     Linda* const linda{ lua_toLinda<false>(L, 1) };
-    int pushed, expected_pushed_min, expected_pushed_max;
-    CancelRequest cancel{ CancelRequest::None };
-    keeper_api_t keeper_receive;
-    
-    time_d timeout = -1.0;
-    int key_i = 2;
 
-    if( lua_type( L, 2) == LUA_TNUMBER) // we don't want to use lua_isnumber() because of autocoercion
+    time_d timeout{ -1.0 };
+    int key_i{ 2 };
+
+    if (lua_type(L, 2) == LUA_TNUMBER) // we don't want to use lua_isnumber() because of autocoercion
     {
-        timeout = SIGNAL_TIMEOUT_PREPARE( lua_tonumber( L, 2));
-        ++ key_i;
+        timeout = SIGNAL_TIMEOUT_PREPARE(lua_tonumber(L, 2));
+        ++key_i;
     }
-    else if( lua_isnil( L, 2)) // alternate explicit "no timeout" by passing nil before the key
+    else if (lua_isnil(L, 2)) // alternate explicit "no timeout" by passing nil before the key
     {
-        ++ key_i;
+        ++key_i;
     }
 
+    keeper_api_t keeper_receive;
+    int expected_pushed_min{ 0 }, expected_pushed_max{ 0 };
     // are we in batched mode?
+    BATCH_SENTINEL.push(L);
+    int const is_batched{ lua501_equal(L, key_i, -1) };
+    lua_pop(L, 1);
+    if (is_batched)
+    {
+        // no need to pass linda.batched in the keeper state
+        ++key_i;
+        // make sure the keys are of a valid type
+        check_key_types(L, key_i, key_i);
+        // receive multiple values from a single slot
+        keeper_receive = KEEPER_API(receive_batched);
+        // we expect a user-defined amount of return value
+        expected_pushed_min = (int) luaL_checkinteger(L, key_i + 1);
+        expected_pushed_max = (int) luaL_optinteger(L, key_i + 2, expected_pushed_min);
+        // don't forget to count the key in addition to the values
+        ++expected_pushed_min;
+        ++expected_pushed_max;
+        if (expected_pushed_min > expected_pushed_max)
+        {
+            return luaL_error(L, "batched min/max error");
+        }
+    }
+    else
+    {
+        // make sure the keys are of a valid type
+        check_key_types(L, key_i, lua_gettop(L));
+        // receive a single value, checking multiple slots
+        keeper_receive = KEEPER_API(receive);
+        // we expect a single (value, key) pair of returned values
+        expected_pushed_min = expected_pushed_max = 2;
+    }
+
+    Lane* const lane{ get_lane_from_registry(L) };
+    Keeper* const K{ which_keeper(linda->U->keepers, linda->hashSeed()) };
+    if (K == nullptr)
+        return 0;
+    CancelRequest cancel{ CancelRequest::None };
+    int pushed{ 0 };
+    for (bool try_again{ true };;)
     {
-        int is_batched;
-        lua_pushliteral( L, BATCH_SENTINEL);
-        is_batched = lua501_equal( L, key_i, -1);
-        lua_pop( L, 1);
-        if( is_batched)
+        if (lane != nullptr)
         {
-            // no need to pass linda.batched in the keeper state
-            ++ key_i;
-            // make sure the keys are of a valid type
-            check_key_types( L, key_i, key_i);
-            // receive multiple values from a single slot
-            keeper_receive = KEEPER_API( receive_batched);
-            // we expect a user-defined amount of return value
-            expected_pushed_min = (int)luaL_checkinteger( L, key_i + 1);
-            expected_pushed_max = (int)luaL_optinteger( L, key_i + 2, expected_pushed_min);
-            // don't forget to count the key in addition to the values
-            ++ expected_pushed_min;
-            ++ expected_pushed_max;
-            if( expected_pushed_min > expected_pushed_max)
-            {
-                return luaL_error( L, "batched min/max error");
-            }
+            cancel = lane->cancel_request;
         }
-        else
+        cancel = (cancel != CancelRequest::None) ? cancel : linda->simulate_cancel;
+        // if user wants to cancel, or looped because of a timeout, the call returns without sending anything
+        if (!try_again || cancel != CancelRequest::None)
         {
-            // make sure the keys are of a valid type
-            check_key_types( L, key_i, lua_gettop( L));
-            // receive a single value, checking multiple slots
-            keeper_receive = KEEPER_API( receive);
-            // we expect a single (value, key) pair of returned values
-            expected_pushed_min = expected_pushed_max = 2;
+            pushed = 0;
+            break;
         }
-    }
 
-    {
-        Lane* const s{ get_lane_from_registry(L) };
-        Keeper* const K{ which_keeper(linda->U->keepers, linda->hashSeed()) };
-        if( K == nullptr) return 0;
-        for (bool try_again{ true };;)
+        // all arguments of receive() but the first are passed to the keeper's receive function
+        pushed = keeper_call(linda->U, K->L, keeper_receive, L, linda, key_i);
+        if (pushed < 0)
         {
-            if( s != nullptr)
-            {
-                cancel = s->cancel_request;
-            }
-            cancel = (cancel != CancelRequest::None) ? cancel : linda->simulate_cancel;
-            // if user wants to cancel, or looped because of a timeout, the call returns without sending anything
-            if (!try_again || cancel != CancelRequest::None)
-            {
-                pushed = 0;
-                break;
-            }
+            break;
+        }
+        if (pushed > 0)
+        {
+            ASSERT_L(pushed >= expected_pushed_min && pushed <= expected_pushed_max);
+            // replace sentinels with real nils
+            keeper_toggle_nil_sentinels(L, lua_gettop(L) - pushed, eLM_FromKeeper);
+            // To be done from within the 'K' locking area
+            //
+            SIGNAL_ALL(&linda->read_happened);
+            break;
+        }
 
-            // all arguments of receive() but the first are passed to the keeper's receive function
-            pushed = keeper_call( linda->U, K->L, keeper_receive, L, linda, key_i);
-            if( pushed < 0)
-            {
-                break;
-            }
-            if( pushed > 0)
-            {
-                ASSERT_L( pushed >= expected_pushed_min && pushed <= expected_pushed_max);
-                // replace sentinels with real nils
-                keeper_toggle_nil_sentinels( L, lua_gettop( L) - pushed, eLM_FromKeeper);
-                // To be done from within the 'K' locking area
-                //
-                SIGNAL_ALL( &linda->read_happened);
-                break;
-            }
+        if (timeout == 0.0)
+        {
+            break; /* instant timeout */
+        }
 
-            if( timeout == 0.0)
+        // nothing received, wait until timeout or signalled that we should try again
+        {
+            enum e_status prev_status = ERROR_ST; // prevent 'might be used uninitialized' warnings
+            if (lane != nullptr)
             {
-                break;  /* instant timeout */
+                // change status of lane to "waiting"
+                prev_status = lane->status; // RUNNING, most likely
+                ASSERT_L(prev_status == RUNNING); // but check, just in case
+                lane->status = WAITING;
+                ASSERT_L(lane->waiting_on == nullptr);
+                lane->waiting_on = &linda->write_happened;
             }
-
-            // nothing received, wait until timeout or signalled that we should try again
+            // not enough data to read: wakeup when data was sent, or when timeout is reached
+            try_again = SIGNAL_WAIT(&linda->write_happened, &K->keeper_cs, timeout);
+            if (lane != nullptr)
             {
-                enum e_status prev_status = ERROR_ST; // prevent 'might be used uninitialized' warnings
-                if( s != nullptr)
-                {
-                    // change status of lane to "waiting"
-                    prev_status = s->status; // RUNNING, most likely
-                    ASSERT_L( prev_status == RUNNING); // but check, just in case
-                    s->status = WAITING;
-                    ASSERT_L( s->waiting_on == nullptr);
-                    s->waiting_on = &linda->write_happened;
-                }
-                // not enough data to read: wakeup when data was sent, or when timeout is reached
-                try_again = SIGNAL_WAIT( &linda->write_happened, &K->keeper_cs, timeout);
-                if( s != nullptr)
-                {
-                    s->waiting_on = nullptr;
-                    s->status = prev_status;
-                }
+                lane->waiting_on = nullptr;
+                lane->status = prev_status;
             }
         }
     }
 
-    if( pushed < 0)
+    if (pushed < 0)
     {
-        return luaL_error( L, "tried to copy unsupported types");
+        return luaL_error(L, "tried to copy unsupported types");
     }
 
-    switch( cancel)
+    switch (cancel)
     {
         case CancelRequest::Soft:
         // if user wants to soft-cancel, the call returns CANCEL_ERROR
@@ -520,53 +514,49 @@ LUAG_FUNC( linda_receive)
 *
 * Existing slot value is replaced, and possible queued entries removed.
 */
-LUAG_FUNC( linda_set)
+LUAG_FUNC(linda_set)
 {
     Linda* const linda{ lua_toLinda<false>(L, 1) };
-    int pushed;
     bool const has_value{ lua_gettop(L) > 2 };
-
     // make sure the key is of a valid type (throws an error if not the case)
-    check_key_types( L, 2, 2);
+    check_key_types(L, 2, 2);
 
+    Keeper* const K{ which_keeper(linda->U->keepers, linda->hashSeed()) };
+    int pushed{ 0 };
+    if (linda->simulate_cancel == CancelRequest::None)
     {
-        Keeper* const K{ which_keeper(linda->U->keepers, linda->hashSeed()) };
-
-        if (linda->simulate_cancel == CancelRequest::None)
+        if (has_value)
+        {
+            // convert nils to some special non-nil sentinel in sent values
+            keeper_toggle_nil_sentinels(L, 3, eLM_ToKeeper);
+        }
+        pushed = keeper_call(linda->U, K->L, KEEPER_API(set), L, linda, 2);
+        if (pushed >= 0) // no error?
         {
-            if( has_value)
+            ASSERT_L(pushed == 0 || pushed == 1);
+
+            if (has_value)
             {
-                // convert nils to some special non-nil sentinel in sent values
-                keeper_toggle_nil_sentinels( L, 3, eLM_ToKeeper);
+                // we put some data in the slot, tell readers that they should wake
+                SIGNAL_ALL(&linda->write_happened); // To be done from within the 'K' locking area
             }
-            pushed = keeper_call( linda->U, K->L, KEEPER_API( set), L, linda, 2);
-            if( pushed >= 0) // no error?
+            if (pushed == 1)
             {
-                ASSERT_L( pushed == 0 || pushed == 1);
-
-                if( has_value)
-                {
-                    // we put some data in the slot, tell readers that they should wake
-                    SIGNAL_ALL( &linda->write_happened); // To be done from within the 'K' locking area
-                }
-                if( pushed == 1)
-                {
-                    // the key was full, but it is no longer the case, tell writers they should wake
-                    ASSERT_L( lua_type( L, -1) == LUA_TBOOLEAN && lua_toboolean( L, -1) == 1);
-                    SIGNAL_ALL( &linda->read_happened); // To be done from within the 'K' locking area
-                }
+                // the key was full, but it is no longer the case, tell writers they should wake
+                ASSERT_L(lua_type(L, -1) == LUA_TBOOLEAN && lua_toboolean(L, -1) == 1);
+                SIGNAL_ALL(&linda->read_happened); // To be done from within the 'K' locking area
             }
         }
-        else // linda is cancelled
-        {
-            // do nothing and return lanes.cancel_error
-            CANCEL_ERROR.push(L);
-            pushed = 1;
-        }
+    }
+    else // linda is cancelled
+    {
+        // do nothing and return lanes.cancel_error
+        CANCEL_ERROR.push(L);
+        pushed = 1;
     }
 
     // must trigger any error after keeper state has been released
-    return (pushed < 0) ? luaL_error( L, "tried to copy unsupported types") : pushed;
+    return (pushed < 0) ? luaL_error(L, "tried to copy unsupported types") : pushed;
 }
 
 // #################################################################################################
@@ -576,21 +566,17 @@ LUAG_FUNC( linda_set)
  *
  * Get a count of the pending elements in the specified keys
  */
-LUAG_FUNC( linda_count)
+LUAG_FUNC(linda_count)
 {
     Linda* const linda{ lua_toLinda<false>(L, 1) };
-    int pushed;
-
     // make sure the keys are of a valid type
-    check_key_types( L, 2, lua_gettop( L));
+    check_key_types(L, 2, lua_gettop(L));
 
+    Keeper* const K{ which_keeper(linda->U->keepers, linda->hashSeed()) };
+    int const pushed{ keeper_call(linda->U, K->L, KEEPER_API(count), L, linda, 2) };
+    if (pushed < 0)
     {
-        Keeper* const K{ which_keeper(linda->U->keepers, linda->hashSeed()) };
-        pushed = keeper_call( linda->U, K->L, KEEPER_API( count), L, linda, 2);
-        if( pushed < 0)
-        {
-            return luaL_error( L, "tried to count an invalid key");
-        }
+        return luaL_error(L, "tried to count an invalid key");
     }
     return pushed;
 }
@@ -602,39 +588,36 @@ LUAG_FUNC( linda_count)
 *
 * Get one or more values from Linda.
 */
-LUAG_FUNC( linda_get)
+LUAG_FUNC(linda_get)
 {
     Linda* const linda{ lua_toLinda<false>(L, 1) };
-    int pushed;
-    lua_Integer count = luaL_optinteger( L, 3, 1);
-    luaL_argcheck( L, count >= 1, 3, "count should be >= 1");
-    luaL_argcheck( L, lua_gettop( L) <= 3, 4, "too many arguments");
-
+    lua_Integer const count{ luaL_optinteger(L, 3, 1) };
+    luaL_argcheck(L, count >= 1, 3, "count should be >= 1");
+    luaL_argcheck(L, lua_gettop(L) <= 3, 4, "too many arguments");
     // make sure the key is of a valid type (throws an error if not the case)
-    check_key_types( L, 2, 2);
+    check_key_types(L, 2, 2);
+
+    int pushed{ 0 };
+    if (linda->simulate_cancel == CancelRequest::None)
     {
         Keeper* const K{ which_keeper(linda->U->keepers, linda->hashSeed()) };
-
-        if (linda->simulate_cancel == CancelRequest::None)
+        pushed = keeper_call(linda->U, K->L, KEEPER_API(get), L, linda, 2);
+        if (pushed > 0)
         {
-            pushed = keeper_call( linda->U, K->L, KEEPER_API( get), L, linda, 2);
-            if( pushed > 0)
-            {
-                keeper_toggle_nil_sentinels( L, lua_gettop( L) - pushed, eLM_FromKeeper);
-            }
-        }
-        else // linda is cancelled
-        {
-            // do nothing and return lanes.cancel_error
-            CANCEL_ERROR.push(L);
-            pushed = 1;
-        }
-        // an error can be raised if we attempt to read an unregistered function
-        if( pushed < 0)
-        {
-            return luaL_error( L, "tried to copy unsupported types");
+            keeper_toggle_nil_sentinels(L, lua_gettop(L) - pushed, eLM_FromKeeper);
         }
     }
+    else // linda is cancelled
+    {
+        // do nothing and return lanes.cancel_error
+        CANCEL_ERROR.push(L);
+        pushed = 1;
+    }
+    // an error can be raised if we attempt to read an unregistered function
+    if (pushed < 0)
+    {
+        return luaL_error(L, "tried to copy unsupported types");
+    }
 
     return pushed;
 }
@@ -650,8 +633,6 @@ LUAG_FUNC( linda_get)
 LUAG_FUNC( linda_limit)
 {
     Linda* const linda{ lua_toLinda<false>(L, 1) };
-    int pushed;
-
     // make sure we got 3 arguments: the linda, a key and a limit
     luaL_argcheck( L, lua_gettop( L) == 3, 2, "wrong number of arguments");
     // make sure we got a numeric limit
@@ -659,26 +640,24 @@ LUAG_FUNC( linda_limit)
     // make sure the key is of a valid type
     check_key_types( L, 2, 2);
 
+    int pushed{ 0 };
+    if (linda->simulate_cancel == CancelRequest::None)
     {
         Keeper* const K{ which_keeper(linda->U->keepers, linda->hashSeed()) };
-
-        if (linda->simulate_cancel == CancelRequest::None)
-        {
-            pushed = keeper_call( linda->U, K->L, KEEPER_API( limit), L, linda, 2);
-            ASSERT_L( pushed == 0 || pushed == 1); // no error, optional boolean value saying if we should wake blocked writer threads
-            if( pushed == 1)
-            {
-                ASSERT_L( lua_type( L, -1) == LUA_TBOOLEAN && lua_toboolean( L, -1) == 1);
-                SIGNAL_ALL( &linda->read_happened); // To be done from within the 'K' locking area
-            }
-        }
-        else // linda is cancelled
+        pushed = keeper_call(linda->U, K->L, KEEPER_API(limit), L, linda, 2);
+        ASSERT_L( pushed == 0 || pushed == 1); // no error, optional boolean value saying if we should wake blocked writer threads
+        if( pushed == 1)
         {
-            // do nothing and return lanes.cancel_error
-            CANCEL_ERROR.push(L);
-            pushed = 1;
+            ASSERT_L( lua_type( L, -1) == LUA_TBOOLEAN && lua_toboolean( L, -1) == 1);
+            SIGNAL_ALL( &linda->read_happened); // To be done from within the 'K' locking area
         }
     }
+    else // linda is cancelled
+    {
+        // do nothing and return lanes.cancel_error
+        CANCEL_ERROR.push(L);
+        pushed = 1;
+    }
     // propagate pushed boolean if any
     return pushed;
 }
@@ -690,35 +669,34 @@ LUAG_FUNC( linda_limit)
 *
 * Signal linda so that waiting threads wake up as if their own lane was cancelled
 */
-LUAG_FUNC( linda_cancel)
+LUAG_FUNC(linda_cancel)
 {
     Linda* const linda{ lua_toLinda<false>(L, 1) };
-    char const* who = luaL_optstring( L, 2, "both");
-
+    char const* who = luaL_optstring(L, 2, "both");
     // make sure we got 3 arguments: the linda, a key and a limit
-    luaL_argcheck( L, lua_gettop( L) <= 2, 2, "wrong number of arguments");
+    luaL_argcheck(L, lua_gettop(L) <= 2, 2, "wrong number of arguments");
 
     linda->simulate_cancel = CancelRequest::Soft;
-    if( strcmp( who, "both") == 0) // tell everyone writers to wake up
+    if (strcmp(who, "both") == 0) // tell everyone writers to wake up
     {
-        SIGNAL_ALL( &linda->write_happened);
-        SIGNAL_ALL( &linda->read_happened);
+        SIGNAL_ALL(&linda->write_happened);
+        SIGNAL_ALL(&linda->read_happened);
     }
-    else if( strcmp( who, "none") == 0) // reset flag
+    else if (strcmp(who, "none") == 0) // reset flag
     {
         linda->simulate_cancel = CancelRequest::None;
     }
-    else if( strcmp( who, "read") == 0) // tell blocked readers to wake up
+    else if (strcmp(who, "read") == 0) // tell blocked readers to wake up
     {
-        SIGNAL_ALL( &linda->write_happened);
+        SIGNAL_ALL(&linda->write_happened);
     }
-    else if( strcmp( who, "write") == 0) // tell blocked writers to wake up
+    else if (strcmp(who, "write") == 0) // tell blocked writers to wake up
     {
-        SIGNAL_ALL( &linda->read_happened);
+        SIGNAL_ALL(&linda->read_happened);
     }
     else
     {
-        return luaL_error( L, "unknown wake hint '%s'", who);
+        return luaL_error(L, "unknown wake hint '%s'", who);
     }
     return 0;
 }
@@ -735,10 +713,10 @@ LUAG_FUNC( linda_cancel)
 * different userdata and won't be known to be essentially the same deep one
 * without this.
 */
-LUAG_FUNC( linda_deep)
+LUAG_FUNC(linda_deep)
 {
     Linda* const linda{ lua_toLinda<false>(L, 1) };
-    lua_pushlightuserdata( L, linda); // just the address
+    lua_pushlightuserdata(L, linda); // just the address
     return 1;
 }
 
@@ -756,21 +734,21 @@ template <bool OPT>
 static int linda_tostring(lua_State* L, int idx_)
 {
     Linda* const linda{ lua_toLinda<OPT>(L, idx_) };
-    if( linda != nullptr)
+    if (linda != nullptr)
     {
         char text[128];
         int len;
-        if( linda->getName())
-            len = sprintf( text, "Linda: %.*s", (int)sizeof(text) - 8, linda->getName());
+        if (linda->getName())
+            len = sprintf(text, "Linda: %.*s", (int) sizeof(text) - 8, linda->getName());
         else
-            len = sprintf( text, "Linda: %p", linda);
-        lua_pushlstring( L, text, len);
+            len = sprintf(text, "Linda: %p", linda);
+        lua_pushlstring(L, text, len);
         return 1;
     }
     return 0;
 }
 
-LUAG_FUNC( linda_tostring)
+LUAG_FUNC(linda_tostring)
 {
     return linda_tostring<false>(L, 1);
 }
@@ -784,25 +762,25 @@ LUAG_FUNC( linda_tostring)
 *
 * Useful for concatenation or debugging purposes
 */
-LUAG_FUNC( linda_concat)
-{                                   // linda1? linda2?
+LUAG_FUNC(linda_concat)
+{ // linda1? linda2?
     bool atLeastOneLinda{ false };
     // Lua semantics enforce that one of the 2 arguments is a Linda, but not necessarily both.
-    if( linda_tostring<true>( L, 1))
+    if (linda_tostring<true>(L, 1))
     {
         atLeastOneLinda = true;
-        lua_replace( L, 1);
+        lua_replace(L, 1);
     }
-    if( linda_tostring<true>( L, 2))
+    if (linda_tostring<true>(L, 2))
     {
         atLeastOneLinda = true;
-        lua_replace( L, 2);
+        lua_replace(L, 2);
     }
-    if( !atLeastOneLinda) // should not be possible
+    if (!atLeastOneLinda) // should not be possible
     {
-        return luaL_error( L, "internal error: linda_concat called on non-Linda");
+        return luaL_error(L, "internal error: linda_concat called on non-Linda");
     }
-    lua_concat( L, 2);
+    lua_concat(L, 2);
     return 1;
 }
 
@@ -812,17 +790,19 @@ LUAG_FUNC( linda_concat)
  * table = linda:dump()
  * return a table listing all pending data inside the linda
  */
-LUAG_FUNC( linda_dump)
+LUAG_FUNC(linda_dump)
 {
     Linda* const linda{ lua_toLinda<false>(L, 1) };
     return keeper_push_linda_storage(linda->U, L, linda, linda->hashSeed());
 }
 
+// #################################################################################################
+
 /*
  * table = linda:dump()
  * return a table listing all pending data inside the linda
  */
-LUAG_FUNC( linda_towatch)
+LUAG_FUNC(linda_towatch)
 {
     Linda* const linda{ lua_toLinda<false>(L, 1) };
     int pushed{ keeper_push_linda_storage(linda->U, L, linda, linda->hashSeed()) };
@@ -834,6 +814,8 @@ LUAG_FUNC( linda_towatch)
     return pushed;
 }
 
+// #################################################################################################
+
 /*
 * Identity function of a shared userdata object.
 * 
@@ -868,51 +850,51 @@ static void* linda_id( lua_State* L, DeepOp op_)
             char const* linda_name = nullptr;
             unsigned long linda_group = 0;
             // should have a string and/or a number of the stack as parameters (name and group)
-            switch( lua_gettop( L))
+            switch (lua_gettop(L))
             {
                 default: // 0
                 break;
 
                 case 1: // 1 parameter, either a name or a group
-                if( lua_type( L, -1) == LUA_TSTRING)
+                if (lua_type(L, -1) == LUA_TSTRING)
                 {
-                    linda_name = lua_tolstring( L, -1, &name_len);
+                    linda_name = lua_tolstring(L, -1, &name_len);
                 }
                 else
                 {
-                    linda_group = (unsigned long) lua_tointeger( L, -1);
+                    linda_group = (unsigned long) lua_tointeger(L, -1);
                 }
                 break;
 
                 case 2: // 2 parameters, a name and group, in that order
-                linda_name = lua_tolstring( L, -2, &name_len);
-                linda_group = (unsigned long) lua_tointeger( L, -1);
+                linda_name = lua_tolstring(L, -2, &name_len);
+                linda_group = (unsigned long) lua_tointeger(L, -1);
                 break;
             }
 
             /* The deep data is allocated separately of Lua stack; we might no
-            * longer be around when last reference to it is being released.
-            * One can use any memory allocation scheme.
-            * just don't use L's allocF because we don't know which state will get the honor of GCing the linda
-            */
+             * longer be around when last reference to it is being released.
+             * One can use any memory allocation scheme.
+             * just don't use L's allocF because we don't know which state will get the honor of GCing the linda
+             */
             Universe* const U{ universe_get(L) };
-            Linda* s{ new (U) Linda{ U, linda_group, linda_name, name_len } };
-            return s;
+            Linda* linda{ new (U) Linda{ U, linda_group, linda_name, name_len } };
+            return linda;
         }
 
         case eDO_delete:
         {
             Linda* const linda{ lua_tolightuserdata<Linda>(L, 1) };
-            ASSERT_L( linda);
+            ASSERT_L(linda);
 
             // Clean associated structures in the keeper state.
             Keeper* const K{ keeper_acquire(linda->U->keepers, linda->hashSeed()) };
-            if( K && K->L) // can be nullptr if this happens during main state shutdown (lanes is GC'ed -> no keepers -> no need to cleanup)
+            if (K && K->L) // can be nullptr if this happens during main state shutdown (lanes is GC'ed -> no keepers -> no need to cleanup)
             {
                 // hopefully this won't ever raise an error as we would jump to the closest pcall site while forgetting to release the keeper mutex...
-                keeper_call( linda->U, K->L, KEEPER_API( clear), L, linda, 0);
+                keeper_call(linda->U, K->L, KEEPER_API(clear), L, linda, 0);
             }
-            keeper_release( K);
+            keeper_release(K);
 
             delete linda; // operator delete overload ensures things go as expected
             return nullptr;
@@ -920,73 +902,72 @@ static void* linda_id( lua_State* L, DeepOp op_)
 
         case eDO_metatable:
         {
-
             STACK_CHECK_START_REL(L, 0);
-            lua_newtable( L);
+            lua_newtable(L);
             // metatable is its own index
-            lua_pushvalue( L, -1);
-            lua_setfield( L, -2, "__index");
+            lua_pushvalue(L, -1);
+            lua_setfield(L, -2, "__index");
 
             // protect metatable from external access
-            lua_pushliteral( L, "Linda");
-            lua_setfield( L, -2, "__metatable");
+            lua_pushliteral(L, "Linda");
+            lua_setfield(L, -2, "__metatable");
 
-            lua_pushcfunction( L, LG_linda_tostring);
-            lua_setfield( L, -2, "__tostring");
+            lua_pushcfunction(L, LG_linda_tostring);
+            lua_setfield(L, -2, "__tostring");
 
             // Decoda __towatch support
-            lua_pushcfunction( L, LG_linda_towatch);
-            lua_setfield( L, -2, "__towatch");
+            lua_pushcfunction(L, LG_linda_towatch);
+            lua_setfield(L, -2, "__towatch");
 
-            lua_pushcfunction( L, LG_linda_concat);
-            lua_setfield( L, -2, "__concat");
+            lua_pushcfunction(L, LG_linda_concat);
+            lua_setfield(L, -2, "__concat");
 
             // protected calls, to ensure associated keeper is always released even in case of error
             // all function are the protected call wrapper, where the actual operation is provided as upvalue
             // note that this kind of thing can break function lookup as we use the function pointer here and there
 
-            lua_pushcfunction( L, LG_linda_send);
-            lua_pushcclosure( L, LG_linda_protected_call, 1);
-            lua_setfield( L, -2, "send");
+            lua_pushcfunction(L, LG_linda_send);
+            lua_pushcclosure(L, LG_linda_protected_call, 1);
+            lua_setfield(L, -2, "send");
 
-            lua_pushcfunction( L, LG_linda_receive);
-            lua_pushcclosure( L, LG_linda_protected_call, 1);
-            lua_setfield( L, -2, "receive");
+            lua_pushcfunction(L, LG_linda_receive);
+            lua_pushcclosure(L, LG_linda_protected_call, 1);
+            lua_setfield(L, -2, "receive");
 
-            lua_pushcfunction( L, LG_linda_limit);
-            lua_pushcclosure( L, LG_linda_protected_call, 1);
-            lua_setfield( L, -2, "limit");
+            lua_pushcfunction(L, LG_linda_limit);
+            lua_pushcclosure(L, LG_linda_protected_call, 1);
+            lua_setfield(L, -2, "limit");
 
-            lua_pushcfunction( L, LG_linda_set);
-            lua_pushcclosure( L, LG_linda_protected_call, 1);
-            lua_setfield( L, -2, "set");
+            lua_pushcfunction(L, LG_linda_set);
+            lua_pushcclosure(L, LG_linda_protected_call, 1);
+            lua_setfield(L, -2, "set");
 
-            lua_pushcfunction( L, LG_linda_count);
-            lua_pushcclosure( L, LG_linda_protected_call, 1);
-            lua_setfield( L, -2, "count");
+            lua_pushcfunction(L, LG_linda_count);
+            lua_pushcclosure(L, LG_linda_protected_call, 1);
+            lua_setfield(L, -2, "count");
 
-            lua_pushcfunction( L, LG_linda_get);
-            lua_pushcclosure( L, LG_linda_protected_call, 1);
-            lua_setfield( L, -2, "get");
+            lua_pushcfunction(L, LG_linda_get);
+            lua_pushcclosure(L, LG_linda_protected_call, 1);
+            lua_setfield(L, -2, "get");
 
-            lua_pushcfunction( L, LG_linda_cancel);
-            lua_setfield( L, -2, "cancel");
+            lua_pushcfunction(L, LG_linda_cancel);
+            lua_setfield(L, -2, "cancel");
 
-            lua_pushcfunction( L, LG_linda_deep);
-            lua_setfield( L, -2, "deep");
+            lua_pushcfunction(L, LG_linda_deep);
+            lua_setfield(L, -2, "deep");
 
-            lua_pushcfunction( L, LG_linda_dump);
-            lua_pushcclosure( L, LG_linda_protected_call, 1);
-            lua_setfield( L, -2, "dump");
+            lua_pushcfunction(L, LG_linda_dump);
+            lua_pushcclosure(L, LG_linda_protected_call, 1);
+            lua_setfield(L, -2, "dump");
 
             // some constants
-            lua_pushliteral( L, BATCH_SENTINEL);
-            lua_setfield( L, -2, "batched");
+            BATCH_SENTINEL.push(L);
+            lua_setfield(L, -2, "batched");
 
             NIL_SENTINEL.push(L);
-            lua_setfield( L, -2, "null");
+            lua_setfield(L, -2, "null");
 
-            STACK_CHECK( L, 1);
+            STACK_CHECK(L, 1);
             return nullptr;
         }
 
@@ -1001,24 +982,26 @@ static void* linda_id( lua_State* L, DeepOp op_)
     }
 }
 
+// #################################################################################################
+
 /*
  * ud = lanes.linda( [name[,group]])
  *
  * returns a linda object, or raises an error if creation failed
  */
-LUAG_FUNC( linda)
+LUAG_FUNC(linda)
 {
-    int const top = lua_gettop( L);
-    luaL_argcheck( L, top <= 2, top, "too many arguments");
-    if( top == 1)
+    int const top = lua_gettop(L);
+    luaL_argcheck(L, top <= 2, top, "too many arguments");
+    if (top == 1)
     {
-        int const t = lua_type( L, 1);
-        luaL_argcheck( L, t == LUA_TSTRING || t == LUA_TNUMBER, 1, "wrong parameter (should be a string or a number)");
+        int const t = lua_type(L, 1);
+        luaL_argcheck(L, t == LUA_TSTRING || t == LUA_TNUMBER, 1, "wrong parameter (should be a string or a number)");
     }
-    else if( top == 2)
+    else if (top == 2)
     {
-        luaL_checktype( L, 1, LUA_TSTRING);
-        luaL_checktype( L, 2, LUA_TNUMBER);
+        luaL_checktype(L, 1, LUA_TSTRING);
+        luaL_checktype(L, 2, LUA_TNUMBER);
     }
-    return luaG_newdeepuserdata( L, linda_id, 0);
+    return luaG_newdeepuserdata(L, linda_id, 0);
 }
diff --git a/src/uniquekey.h b/src/uniquekey.h
index 777d640..93aaf37 100644
--- a/src/uniquekey.h
+++ b/src/uniquekey.h
@@ -3,6 +3,8 @@
 #include "compat.h"
 #include "macros_and_utils.h"
 
+#include <bit>
+
 class UniqueKey
 {
     private:
@@ -31,13 +33,11 @@ class UniqueKey
 
     void push(lua_State* const L) const
     {
-        // unfortunately, converting a scalar to a pointer must go through a C cast
-        lua_pushlightuserdata(L, (void*) m_storage);
+        lua_pushlightuserdata(L, std::bit_cast<void*>(m_storage));
     }
     bool equals(lua_State* const L, int i) const
     {
-        // unfortunately, converting a scalar to a pointer must go through a C cast
-        return lua_touserdata(L, i) == (void*) m_storage;
+        return lua_touserdata(L, i) == std::bit_cast<void*>(m_storage);
     }
     void query_registry(lua_State* const L) const
     {