[socket-nif] Add proper recv timeout handling

Added proper recv timeout handling.
Made use of the enif_select(mode = cancel) feature. Each
time a timeout expires, the "active" recv (the surrent reader
select) has to be cancelled. Not yet tested...something for
the new test suite...

Also, added support for getopt(controlling_pprocess) that,
for some reason, was not yet implemented.

OTP-14831

3 files changed, 727 insertions, 81 deletions

diff --git a/erts/emulator/nifs/common/socket_int.h b/erts/emulator/nifs/common/socket_int.h
index 3595c483d7..c3595e495d 100644
--- a/erts/emulator/nifs/common/socket_int.h
+++ b/erts/emulator/nifs/common/socket_int.h
@@ -184,6 +184,7 @@ extern ERL_NIF_TERM esock_atom_einval;
 #define MKLA(E,A,L)         enif_make_list_from_array((E), (A), (L))
 #define MKEL(E)             enif_make_list((E), 0)
 #define MKMA(E,KA,VA,L,M)   enif_make_map_from_arrays((E), (KA), (VA), (L), (M))
+#define MKPID(E, P)         enif_make_pid((E), (P))
 #define MKREF(E)            enif_make_ref((E))
 #define MKS(E,S)            enif_make_string((E), (S), ERL_NIF_LATIN1)
 #define MKSL(E,S,L)         enif_make_string_len((E), (S), (L), ERL_NIF_LATIN1)
diff --git a/erts/emulator/nifs/common/socket_nif.c b/erts/emulator/nifs/common/socket_nif.c
index c48d6eab00..a6940f788c 100644
--- a/erts/emulator/nifs/common/socket_nif.c
+++ b/erts/emulator/nifs/common/socket_nif.c
@@ -1490,6 +1490,8 @@ static ERL_NIF_TERM ngetopt_otp_debug(ErlNifEnv*        env,
                                       SocketDescriptor* descP);
 static ERL_NIF_TERM ngetopt_otp_iow(ErlNifEnv*        env,
                                     SocketDescriptor* descP);
+static ERL_NIF_TERM ngetopt_otp_ctrl_proc(ErlNifEnv*        env,
+                                          SocketDescriptor* descP);
 static ERL_NIF_TERM ngetopt_native(ErlNifEnv*        env,
                                    SocketDescriptor* descP,
                                    int               level,
@@ -1849,6 +1851,11 @@ static ERL_NIF_TERM ncancel_send_waiting(ErlNifEnv*        env,
 static ERL_NIF_TERM ncancel_recv(ErlNifEnv*        env,
                                  SocketDescriptor* descP,
                                  ERL_NIF_TERM      opRef);
+static ERL_NIF_TERM ncancel_recv_current(ErlNifEnv*        env,
+                                         SocketDescriptor* descP);
+static ERL_NIF_TERM ncancel_recv_waiting(ErlNifEnv*        env,
+                                         SocketDescriptor* descP,
+                                         ERL_NIF_TERM      opRef);
 static ERL_NIF_TERM ncancel_read_select(ErlNifEnv*        env,
                                         SocketDescriptor* descP,
                                         ERL_NIF_TERM      opRef);
@@ -1911,6 +1918,18 @@ static ERL_NIF_TERM send_check_result(ErlNifEnv*        env,
                                       ssize_t           dataSize,
                                       int               saveErrno,
                                       ERL_NIF_TERM      sendRef);
+static BOOLEAN_T recv_check_reader(ErlNifEnv*        env,
+                                   SocketDescriptor* descP,
+                                   ERL_NIF_TERM      ref,
+                                   ERL_NIF_TERM*     checkResult);
+static char* recv_init_current_reader(ErlNifEnv*        env,
+                                      SocketDescriptor* descP,
+                                      ERL_NIF_TERM      ref);
+static ERL_NIF_TERM recv_update_current_reader(ErlNifEnv*        env,
+                                               SocketDescriptor* descP);
+static void recv_error_current_reader(ErlNifEnv*        env,
+                                      SocketDescriptor* descP,
+                                      ERL_NIF_TERM      reason);
 static ERL_NIF_TERM recv_check_result(ErlNifEnv*        env,
                                       SocketDescriptor* descP,
                                       int               read,
@@ -2150,6 +2169,22 @@ static BOOLEAN_T writer_unqueue(ErlNifEnv*        env,
                                 SocketDescriptor* descP,
                                 const ErlNifPid*  pid);
 
+static BOOLEAN_T reader_search4pid(ErlNifEnv*        env,
+                                   SocketDescriptor* descP,
+                                   ErlNifPid*        pid);
+static ERL_NIF_TERM reader_push(ErlNifEnv*        env,
+                                SocketDescriptor* descP,
+                                ErlNifPid         pid,
+                                ERL_NIF_TERM      ref);
+static BOOLEAN_T reader_pop(ErlNifEnv*        env,
+                            SocketDescriptor* descP,
+                            ErlNifPid*        pid,
+                            ErlNifMonitor*    mon,
+                            ERL_NIF_TERM*     ref);
+static BOOLEAN_T reader_unqueue(ErlNifEnv*        env,
+                                SocketDescriptor* descP,
+                                const ErlNifPid*  pid);
+
 static BOOLEAN_T qsearch4pid(ErlNifEnv*          env,
                              SocketRequestQueue* q,
                              ErlNifPid*          pid);
@@ -2159,7 +2194,6 @@ static SocketRequestQueueElement* qpop(SocketRequestQueue* q);
 static BOOLEAN_T qunqueue(ErlNifEnv*          env,
                           SocketRequestQueue* q,
                           const ErlNifPid*    pid);
-
 /*
 #if defined(HAVE_SYS_UN_H) || defined(SO_BINDTODEVICE)
 static size_t my_strnlen(const char *s, size_t maxlen);
@@ -2175,6 +2209,15 @@ static void socket_down(ErlNifEnv*           env,
 			void*                obj,
 			const ErlNifPid*     pid,
 			const ErlNifMonitor* mon);
+static void socket_down_acceptor(ErlNifEnv*        env,
+                                 SocketDescriptor* descP,
+                                 const ErlNifPid*  pid);
+static void socket_down_writer(ErlNifEnv*        env,
+                               SocketDescriptor* descP,
+                               const ErlNifPid*  pid);
+static void socket_down_reader(ErlNifEnv*        env,
+                               SocketDescriptor* descP,
+                               const ErlNifPid*  pid);
 
 /*
 static char* send_msg_error_closed(ErlNifEnv*   env,
@@ -3986,6 +4029,8 @@ ERL_NIF_TERM nsendmsg(ErlNifEnv*        env,
             if (ctrlBuf != NULL) FREE(ctrlBuf);
             return esock_make_error_str(env, xres);
         }
+    } else {
+        ctrlBufUsed = 0;
     }
     msgHdr.msg_control    = ctrlBuf;
     msgHdr.msg_controllen = ctrlBufUsed;
@@ -4168,6 +4213,7 @@ ERL_NIF_TERM nrecv(ErlNifEnv*        env,
 {
     ssize_t      read;
     ErlNifBinary buf;
+    ERL_NIF_TERM readerCheck;
     int          save_errno;
     int          bufSz = (len ? len : descP->rBufSz);
 
@@ -4179,6 +4225,10 @@ ERL_NIF_TERM nrecv(ErlNifEnv*        env,
     if (!descP->isReadable)
         return enif_make_badarg(env);
 
+    /* Check if there is already a current reader and if its us */
+    if (!recv_check_reader(env, descP, recvRef, &readerCheck))
+        return readerCheck;
+    
     /* Allocate a buffer:
      * Either as much as we want to read or (if zero (0)) use the "default"
      * size (what has been configured).
@@ -4315,6 +4365,7 @@ ERL_NIF_TERM nrecvfrom(ErlNifEnv*        env,
     ssize_t       read;
     int           save_errno;
     ErlNifBinary  buf;
+    ERL_NIF_TERM  readerCheck;
     int           bufSz = (len ? len : descP->rBufSz);
 
     SSDBG( descP, ("SOCKET", "nrecvfrom -> entry with"
@@ -4325,6 +4376,10 @@ ERL_NIF_TERM nrecvfrom(ErlNifEnv*        env,
     if (!descP->isReadable)
         return enif_make_badarg(env);
 
+    /* Check if there is already a current reader and if its us */
+    if (!recv_check_reader(env, descP, recvRef, &readerCheck))
+        return readerCheck;
+    
     /* Allocate a buffer:
      * Either as much as we want to read or (if zero (0)) use the "default"
      * size (what has been configured).
@@ -4476,6 +4531,7 @@ ERL_NIF_TERM nrecvmsg(ErlNifEnv*        env,
     struct iovec  iov[1];  // Shall we always use 1?
     ErlNifBinary  data[1]; // Shall we always use 1?
     ErlNifBinary  ctrl;
+    ERL_NIF_TERM  readerCheck;
     SocketAddress addr;
 
     SSDBG( descP, ("SOCKET", "nrecvmsg -> entry with"
@@ -4487,6 +4543,10 @@ ERL_NIF_TERM nrecvmsg(ErlNifEnv*        env,
     if (!descP->isReadable)
         return enif_make_badarg(env);
 
+    /* Check if there is already a current reader and if its us */
+    if (!recv_check_reader(env, descP, recvRef, &readerCheck))
+        return readerCheck;
+    
     /*
     for (i = 0; i < sizeof(buf); i++) {
         if (!ALLOC_BIN(bifSz, &buf[i]))
@@ -8093,7 +8153,7 @@ ERL_NIF_TERM ngetopt_otp(ErlNifEnv*        env,
     ERL_NIF_TERM result;
 
     SSDBG( descP,
-           ("SOCKET", "ngetopt_opt -> entry with"
+           ("SOCKET", "ngetopt_otp -> entry with"
             "\r\n   eOpt: %d"
             "\r\n", eOpt) );
 
@@ -8106,13 +8166,17 @@ ERL_NIF_TERM ngetopt_otp(ErlNifEnv*        env,
         result = ngetopt_otp_iow(env, descP);
         break;
 
+    case SOCKET_OPT_OTP_CTRL_PROC:
+        result = ngetopt_otp_ctrl_proc(env, descP);
+        break;
+
     default:
         result = esock_make_error(env, esock_atom_einval);
         break;
     }
 
     SSDBG( descP,
-           ("SOCKET", "ngetopt_opt -> done when"
+           ("SOCKET", "ngetopt_otp -> done when"
             "\r\n   result: %T"
             "\r\n", result) );
 
@@ -8144,6 +8208,18 @@ ERL_NIF_TERM ngetopt_otp_iow(ErlNifEnv*        env,
 }
 
 
+/* ngetopt_otp_ctrl_proc - Handle the OTP (level) controlling_process options
+ */
+static
+ERL_NIF_TERM ngetopt_otp_ctrl_proc(ErlNifEnv*        env,
+                                   SocketDescriptor* descP)
+{
+    ERL_NIF_TERM eVal = MKPID(env, &descP->ctrlPid);
+
+    return esock_make_ok2(env, eVal);
+}
+
+
 
 /* The option has *not* been encoded. Instead it has been provided
  * in "native mode" (option is provided as is). In this case it will have the
@@ -10752,6 +10828,8 @@ ERL_NIF_TERM ncancel_send(ErlNifEnv*        env,
 {
     ERL_NIF_TERM res;
 
+    MLOCK(descP->writeMtx);
+
     SSDBG( descP,
            ("SOCKET", "ncancel_send -> entry with"
             "\r\n   opRef: %T"
@@ -10759,8 +10837,6 @@ ERL_NIF_TERM ncancel_send(ErlNifEnv*        env,
             "\r\n", opRef,
             ((descP->currentWriterP == NULL) ? "without writer" : "with writer")) );
 
-    MLOCK(descP->writeMtx);
-
     if (descP->currentWriterP != NULL) {
         if (COMPARE(opRef, descP->currentWriter.ref) == 0) {
             res = ncancel_send_current(env, descP);
@@ -10859,14 +10935,116 @@ ERL_NIF_TERM ncancel_send_waiting(ErlNifEnv*        env,
 
 /* *** ncancel_recv ***
  *
- *
+ * Cancel a read operation.
+ * Its either the current reader or one of the waiting readers.
  */
 static
 ERL_NIF_TERM ncancel_recv(ErlNifEnv*        env,
                           SocketDescriptor* descP,
                           ERL_NIF_TERM      opRef)
 {
-    return esock_make_error(env, esock_atom_einval);
+    ERL_NIF_TERM res;
+
+    MLOCK(descP->readMtx);
+
+    SSDBG( descP,
+           ("SOCKET", "ncancel_recv -> entry with"
+            "\r\n   opRef: %T"
+            "\r\n   %s"
+            "\r\n", opRef,
+            ((descP->currentReaderP == NULL) ? "without reader" : "with reader")) );
+
+    if (descP->currentReaderP != NULL) {
+        if (COMPARE(opRef, descP->currentReader.ref) == 0) {
+            res = ncancel_recv_current(env, descP);
+        } else {
+            res = ncancel_recv_waiting(env, descP, opRef);
+        }
+    } else {
+        /* Or badarg? */
+        res =  esock_make_error(env, esock_atom_einval);
+    }
+
+    MUNLOCK(descP->readMtx);
+
+    SSDBG( descP,
+           ("SOCKET", "ncancel_recv -> done with result:"
+            "\r\n   %T"
+            "\r\n", res) );
+
+    return res;
+}
+
+
+/* The current reader process has an ongoing select we first must
+ * cancel. Then we must re-activate the "first" (the first
+ * in the reader queue).
+ */
+static
+ERL_NIF_TERM ncancel_recv_current(ErlNifEnv*        env,
+                                  SocketDescriptor* descP)
+{
+    ERL_NIF_TERM res;
+
+    SSDBG( descP, ("SOCKET", "ncancel_recv_current -> entry\r\n") );
+
+    res = ncancel_read_select(env, descP, descP->currentReader.ref);
+
+    SSDBG( descP, ("SOCKET", "ncancel_recv_current -> cancel res: %T\r\n", res) );
+
+    if (reader_pop(env, descP,
+                   &descP->currentReader.pid,
+                   &descP->currentReader.mon,
+                   &descP->currentReader.ref)) {
+        
+        /* There was another one */
+        
+        SSDBG( descP, ("SOCKET", "ncancel_recv_current -> new (active) reader: "
+                       "\r\n   pid: %T"
+                       "\r\n   ref: %T"
+                       "\r\n",
+                       descP->currentReader.pid,
+                       descP->currentReader.ref) );
+        
+        SELECT(env,
+               descP->sock,
+               (ERL_NIF_SELECT_READ),
+               descP, &descP->currentReader.pid, descP->currentReader.ref);
+
+    } else {
+        SSDBG( descP, ("SOCKET", "ncancel_recv_current -> no more readers\r\n") );
+        descP->currentReaderP = NULL;
+    }
+    
+    SSDBG( descP, ("SOCKET", "ncancel_recv_current -> done with result:"
+                   "\r\n   %T"
+                   "\r\n", res) );
+
+    return res;
+}
+
+
+/* These processes have not performed a select, so we can simply
+ * remove them from the reader queue.
+ */
+static
+ERL_NIF_TERM ncancel_recv_waiting(ErlNifEnv*        env,
+                                  SocketDescriptor* descP,
+                                  ERL_NIF_TERM      opRef)
+{
+    ErlNifPid caller;
+
+    if (enif_self(env, &caller) == NULL)
+        return esock_make_error(env, atom_exself);
+
+    /* unqueue request from (reader) queue */
+
+    if (reader_unqueue(env, descP, &caller)) {
+        return esock_atom_ok;
+    } else {
+        /* Race? */
+        return esock_make_error(env, esock_atom_not_found);
+    }
 }
 
 
@@ -10958,7 +11136,8 @@ BOOLEAN_T send_check_writer(ErlNifEnv*        env,
             
             SSDBG( descP,
                    ("SOCKET",
-                    "nsend -> queue (push) result: %T\r\n", checkResult) );
+                    "send_check_writer -> queue (push) result: %T\r\n",
+                    checkResult) );
             
             return FALSE;
 
@@ -11005,7 +11184,8 @@ ERL_NIF_TERM send_check_result(ErlNifEnv*        env,
 
         cnt_inc(&descP->writePkgCnt,  1);
         cnt_inc(&descP->writeByteCnt, written);
-        DEMONP(env, descP, &descP->currentWriter.mon);
+        if (descP->currentWriterP != NULL)
+            DEMONP(env, descP, &descP->currentWriter.mon);
 
         SSDBG( descP,
                ("SOCKET", "send_check_result -> "
@@ -11058,11 +11238,15 @@ ERL_NIF_TERM send_check_result(ErlNifEnv*        env,
 
             res = esock_make_error_errno(env, saveErrno);
 
-            while (writer_pop(env, descP, &pid, &mon, &ref)) {
-                SSDBG( descP,
-                       ("SOCKET", "send_check_result -> abort %T\r\n", pid) );
-                send_msg_nif_abort(env, ref, res, &pid);
-                DEMONP(env, descP, &mon);
+            if (descP->currentWriterP != NULL) {
+                DEMONP(env, descP, &descP->currentWriter.mon);
+
+                while (writer_pop(env, descP, &pid, &mon, &ref)) {
+                    SSDBG( descP,
+                           ("SOCKET", "send_check_result -> abort %T\r\n", pid) );
+                    send_msg_nif_abort(env, ref, res, &pid);
+                    DEMONP(env, descP, &mon);
+                }
             }
             
             return res;
@@ -11087,6 +11271,20 @@ ERL_NIF_TERM send_check_result(ErlNifEnv*        env,
      * so schedule the rest for later.
      */
 
+    if (descP->currentWriterP == NULL) {
+        ErlNifPid caller;
+
+        if (enif_self(env, &caller) == NULL)
+            return esock_make_error(env, atom_exself);
+        descP->currentWriter.pid = caller;
+        if (MONP(env, descP,
+                 &descP->currentWriter.pid,
+                 &descP->currentWriter.mon) > 0)
+            return esock_make_error(env, atom_exmon);
+        descP->currentWriter.ref = enif_make_copy(descP->env, sendRef);
+        descP->currentWriterP    = &descP->currentWriter;
+    }
+
     cnt_inc(&descP->writeWaits, 1);
 
     SELECT(env, descP->sock, (ERL_NIF_SELECT_WRITE),
@@ -11100,6 +11298,167 @@ ERL_NIF_TERM send_check_result(ErlNifEnv*        env,
 }
 
 
+
+/* *** recv_check_reader ***
+ *
+ * Checks if we have a current reader and if that is us. If not, then we must
+ * be made to wait for our turn. This is done by pushing us unto the reader queue.
+ */
+static
+BOOLEAN_T recv_check_reader(ErlNifEnv*        env,
+                            SocketDescriptor* descP,
+                            ERL_NIF_TERM      ref,
+                            ERL_NIF_TERM*     checkResult)
+{
+    if (descP->currentReaderP != NULL) {
+        ErlNifPid caller;
+        
+        if (enif_self(env, &caller) == NULL) {
+            *checkResult = esock_make_error(env, atom_exself);
+            return FALSE;
+        }
+
+        if (!compare_pids(env, &descP->currentReader.pid, &caller)) {
+            /* Not the "current reader", so (maybe) push onto queue */
+
+            SSDBG( descP,
+                   ("SOCKET", "recv_check_reader -> not (current) reader\r\n") );
+
+            if (!reader_search4pid(env, descP, &caller))
+                *checkResult = reader_push(env, descP, caller, ref);
+            else
+                *checkResult = esock_make_error(env, esock_atom_eagain);
+            
+            SSDBG( descP,
+                   ("SOCKET",
+                    "recv_check_reader -> queue (push) result: %T\r\n",
+                    checkResult) );
+            
+            return FALSE;
+
+        }
+        
+    }
+
+    *checkResult = esock_atom_ok; // Does not actually matter in this case, but ...
+
+    return TRUE;
+}
+
+
+
+/* *** recv_init_current_reader ***
+ *
+ * Initiate (maybe) the currentReader structure of the descriptor.
+ * Including monitoring the calling process.
+ */
+static
+char* recv_init_current_reader(ErlNifEnv*        env,
+                               SocketDescriptor* descP,
+                               ERL_NIF_TERM      recvRef)
+{
+    if (descP->currentReaderP == NULL) {
+        ErlNifPid caller;
+
+        if (enif_self(env, &caller) == NULL)
+            return str_exself;
+
+        descP->currentReader.pid = caller;
+        if (MONP(env, descP,
+                 &descP->currentReader.pid,
+                 &descP->currentReader.mon) > 0) {
+            return str_exmon;
+        }
+        descP->currentReader.ref = enif_make_copy(descP->env, recvRef);
+        descP->currentReaderP    = &descP->currentReader;
+    }
+
+    return NULL;
+}
+
+
+
+/* *** recv_update_current_reader ***
+ *
+ * Demonitors the current reader process and pop's the reader queue.
+ * If there is a waiting (reader) process, then it will be assigned
+ * as the new current reader and a new (read) select will be done.
+ */
+
+static
+ERL_NIF_TERM recv_update_current_reader(ErlNifEnv*        env,
+                                        SocketDescriptor* descP)
+{
+    if (descP->currentReaderP != NULL) {
+        
+        DEMONP(env, descP, &descP->currentReader.mon);
+        
+        if (reader_pop(env, descP,
+                       &descP->currentReader.pid,
+                       &descP->currentReader.mon,
+                       &descP->currentReader.ref)) {
+            
+            /* There was another one */
+            
+            SSDBG( descP,
+                   ("SOCKET", "recv_update_current_reader -> new (active) reader: "
+                    "\r\n   pid: %T"
+                    "\r\n   ref: %T"
+                    "\r\n",
+                    descP->currentReader.pid,
+                    descP->currentReader.ref) );
+            
+            SELECT(env,
+                   descP->sock,
+                   (ERL_NIF_SELECT_READ),
+                   descP,
+                   &descP->currentReader.pid,
+                   descP->currentReader.ref);
+            
+        } else {
+            descP->currentWriterP = NULL;
+        }
+    }
+
+    return esock_atom_ok;
+}
+
+
+
+/* *** recv_error_current_reader ***
+ *
+ * Process the current reader and any waiting readers
+ * when a read (fatal) error has occured.
+ * All waiting readers will be "aborted", that is a 
+ * nif_abort message will be sent (with reaf and reason).
+ */
+static
+void recv_error_current_reader(ErlNifEnv*        env,
+                               SocketDescriptor* descP,
+                               ERL_NIF_TERM      reason)
+{
+    if (descP->currentReaderP != NULL) {
+        ErlNifPid     pid;
+        ErlNifMonitor mon;
+        ERL_NIF_TERM  ref;
+
+        DEMONP(env, descP, &descP->currentReader.mon);
+
+        while (reader_pop(env, descP, &pid, &mon, &ref)) {
+            SSDBG( descP,
+                   ("SOCKET", "recv_error_current_reader -> abort %T\r\n", pid) );
+            send_msg_nif_abort(env, ref, reason, &pid);
+            DEMONP(env, descP, &mon);
+        }
+    }
+}
+
+
+
+/* *** recv_check_result ***
+ *
+ * Process the result of a call to recv.
+ */
 static
 ERL_NIF_TERM recv_check_result(ErlNifEnv*        env,
                                SocketDescriptor* descP,
@@ -11109,6 +11468,7 @@ ERL_NIF_TERM recv_check_result(ErlNifEnv*        env,
                                ErlNifBinary*     bufP,
                                ERL_NIF_TERM      recvRef)
 {
+    char*        xres;
     ERL_NIF_TERM data;
 
     SSDBG( descP,
@@ -11129,15 +11489,20 @@ ERL_NIF_TERM recv_check_result(ErlNifEnv*        env,
      */
     
     if ((read == 0) && (descP->type == SOCK_STREAM)) {
+        ERL_NIF_TERM res = esock_make_error(env, atom_closed);
         
         /*
          * When a stream socket peer has performed an orderly shutdown, the return
          * value will be 0 (the traditional "end-of-file" return).
          *
          * *We* do never actually try to read 0 bytes from a stream socket!
+         *
+         * We must also notify any waiting readers!
          */
 
-        return esock_make_error(env, atom_closed);
+        recv_error_current_reader(env, descP, res);
+
+        return res;
 
     }
     
@@ -11173,6 +11538,11 @@ ERL_NIF_TERM recv_check_result(ErlNifEnv*        env,
              * => We choose alt 1 for now.
              */
 
+            cnt_inc(&descP->readByteCnt, read);
+
+            if ((xres = recv_init_current_reader(env, descP, recvRef)) != NULL)
+                return esock_make_error_str(env, xres);
+
             data = MKBIN(env, bufP);
 
             SSDBG( descP,
@@ -11188,16 +11558,24 @@ ERL_NIF_TERM recv_check_result(ErlNifEnv*        env,
 
             /* <KOLLA>
              * WE NEED TO INFORM ANY WAITING READERS
+             *
+             * DEMONP of the current reader!
+             *
              * </KOLLA>
              */
 
-            data = MKBIN(env, bufP);
+            cnt_inc(&descP->readPkgCnt,  1);
+            cnt_inc(&descP->readByteCnt, read);
 
             SSDBG( descP,
                    ("SOCKET",
                     "recv_check_result -> [%d] "
                     "we got exactly what we could fit\r\n", toRead) );
 
+            recv_update_current_reader(env, descP);
+
+            data = MKBIN(env, bufP);
+
             return esock_make_ok3(env, atom_true, data);
 
         }
@@ -11207,6 +11585,7 @@ ERL_NIF_TERM recv_check_result(ErlNifEnv*        env,
         /* +++ Error handling +++ */
 
         if (saveErrno == ECONNRESET)  {
+            ERL_NIF_TERM res = esock_make_error(env, atom_closed);
 
             /* +++ Oups - closed +++ */
 
@@ -11231,12 +11610,14 @@ ERL_NIF_TERM recv_check_result(ErlNifEnv*        env,
             descP->closeLocal = FALSE;
             descP->state      = SOCKET_STATE_CLOSING;
 
+            recv_error_current_reader(env, descP, res);
+
             SELECT(env,
                    descP->sock,
                    (ERL_NIF_SELECT_STOP),
                    descP, NULL, recvRef);
 
-            return esock_make_error(env, atom_closed);
+            return res;
 
         } else if ((saveErrno == ERRNO_BLOCK) ||
                    (saveErrno == EAGAIN)) {
@@ -11248,9 +11629,14 @@ ERL_NIF_TERM recv_check_result(ErlNifEnv*        env,
 
             return esock_make_error(env, esock_atom_eagain);
         } else {
+            ERL_NIF_TERM res = esock_make_error_errno(env, saveErrno);
+
             SSDBG( descP, ("SOCKET", "recv_check_result -> [%d] errno: %d\r\n",
                            toRead, saveErrno) );
-            return esock_make_error_errno(env, saveErrno);
+
+            recv_error_current_reader(env, descP, res);
+
+            return res;
         }
 
     } else {
@@ -11265,19 +11651,24 @@ ERL_NIF_TERM recv_check_result(ErlNifEnv*        env,
 
         if (toRead == 0) {
 
-            /* +++ We got a chunk of data but +++
-             * +++ since we did not fill the  +++
-             * +++ buffer, we must split it   +++
-             * +++ into a sub-binary.         +++
+            /* +++ We got it all, but since we      +++
+             * +++ did not fill the buffer, we      +++
+             * +++ must split it into a sub-binary. +++
              */
 
             SSDBG( descP, ("SOCKET",
                            "recv_check_result -> [%d] split buffer\r\n", toRead) );
 
+            cnt_inc(&descP->readPkgCnt,  1);
+            cnt_inc(&descP->readByteCnt, read);
+
+            recv_update_current_reader(env, descP);
+
             data = MKBIN(env, bufP);
             data = MKSBIN(env, data, 0, read);
 
-            SSDBG( descP, ("SOCKET", "recv_check_result -> [%d] done\r\n", toRead) );
+            SSDBG( descP,
+                   ("SOCKET", "recv_check_result -> [%d] done\r\n", toRead) );
 
             return esock_make_ok3(env, atom_true, data);
 
@@ -11289,6 +11680,8 @@ ERL_NIF_TERM recv_check_result(ErlNifEnv*        env,
             SSDBG( descP, ("SOCKET", "recv_check_result -> [%d] "
                            "only part of message - expect more\r\n", toRead) );
 
+            cnt_inc(&descP->readByteCnt, read);
+
             return esock_make_ok3(env, atom_false, MKBIN(env, bufP));
         }
     }
@@ -13907,10 +14300,10 @@ ERL_NIF_TERM writer_push(ErlNifEnv*        env,
  */
 static
 BOOLEAN_T writer_pop(ErlNifEnv*        env,
-                       SocketDescriptor* descP,
-                       ErlNifPid*        pid,
-                       ErlNifMonitor*    mon,
-                       ERL_NIF_TERM*     ref)
+                     SocketDescriptor* descP,
+                     ErlNifPid*        pid,
+                     ErlNifMonitor*    mon,
+                     ERL_NIF_TERM*     ref)
 {
     SocketRequestQueueElement* e = qpop(&descP->writersQ);
 
@@ -13921,7 +14314,7 @@ BOOLEAN_T writer_pop(ErlNifEnv*        env,
         FREE(e);
         return TRUE;
     } else {
-        /* (acceptors) Queue was empty */
+        /* (writers) Queue was empty */
         // *pid = NULL; we have no null value for pids
         // *mon = NULL; we have no null value for monitors
         *ref = esock_atom_undefined; // Just in case
@@ -13945,6 +14338,92 @@ BOOLEAN_T writer_unqueue(ErlNifEnv*        env,
 
 
 
+/* *** reader search for pid ***
+ *
+ * Search for a pid in the reader queue.
+ */
+static
+BOOLEAN_T reader_search4pid(ErlNifEnv*        env,
+                            SocketDescriptor* descP,
+                            ErlNifPid*        pid)
+{
+    return qsearch4pid(env, &descP->readersQ, pid);
+}
+
+
+/* *** reader push ***
+ *
+ * Push an reader onto the raeder queue.
+ * This happens when we already have atleast one current reader.
+ */
+static
+ERL_NIF_TERM reader_push(ErlNifEnv*        env,
+                         SocketDescriptor* descP,
+                         ErlNifPid         pid,
+                         ERL_NIF_TERM      ref)
+{
+    SocketRequestQueueElement* e    = MALLOC(sizeof(SocketRequestQueueElement));
+    SocketRequestor*           reqP = &e->data;
+    
+    reqP->pid = pid;
+    reqP->ref = enif_make_copy(descP->env, ref);
+    
+    if (MONP(env, descP, &pid, &reqP->mon) > 0) {
+        FREE(reqP);
+        return esock_make_error(env, atom_exmon);
+    }
+    
+    qpush(&descP->readersQ, e);
+    
+    // THIS IS OK => MAKES THE CALLER WAIT FOR ITS TURN
+    return esock_make_error(env, esock_atom_eagain);
+}
+
+
+/* *** reader pop ***
+ *
+ * Pop an writer from the reader queue.
+ */
+static
+BOOLEAN_T reader_pop(ErlNifEnv*        env,
+                     SocketDescriptor* descP,
+                     ErlNifPid*        pid,
+                     ErlNifMonitor*    mon,
+                     ERL_NIF_TERM*     ref)
+{
+    SocketRequestQueueElement* e = qpop(&descP->readersQ);
+
+    if (e != NULL) {
+        *pid = e->data.pid;
+        *mon = e->data.mon;
+        *ref = e->data.ref; // At this point the ref has already been copied (env)
+        FREE(e);
+        return TRUE;
+    } else {
+        /* (readers) Queue was empty */
+        // *pid = NULL; we have no null value for pids
+        // *mon = NULL; we have no null value for monitors
+        *ref = esock_atom_undefined; // Just in case
+        return FALSE;
+    }
+    
+}
+
+
+/* *** reader unqueue ***
+ *
+ * Remove an reader from the reader queue.
+ */
+static
+BOOLEAN_T reader_unqueue(ErlNifEnv*        env,
+                         SocketDescriptor* descP,
+                         const ErlNifPid*  pid)
+{
+    return qunqueue(env, &descP->readersQ, pid);
+}
+
+
+
 
 
 static
@@ -14324,77 +14803,243 @@ void socket_down(ErlNifEnv*           env,
                    "\r\n   pid:  %T"
                    "\r\n", descP->sock, *pid) );
 
-    /* Eventually we should go through the other queues also,
-     * the process can be one of them...
-     *
-     * Currently only the accteptors actuallu use the queues.
-     */
+    
+    if (compare_pids(env, &descP->ctrlPid, pid)) {
+        /* We don't bother with the queue cleanup here - 
+         * we leave it to the stop callback function.
+         */
 
-    if (descP->currentAcceptorP != NULL) {
+        descP->state      = SOCKET_STATE_CLOSING;
+        descP->closeLocal = TRUE;
+        descP->closeRef   = MKREF(env);
+        enif_select(env, descP->sock, (ERL_NIF_SELECT_STOP),
+                    descP, NULL, descP->closeRef);
 
-        /*
-         * We have acceptor(s) (atleast one)
-         *
-         * Check first if its the current acceptor,
-         * and if not check the queue.
-         */
+    } else {
+    
+        /* check all operation queue(s): acceptor, writer and reader. */
+        
+        MLOCK(descP->accMtx);
+        if (descP->currentAcceptorP != NULL)
+            socket_down_acceptor(env, descP, pid);
+        MUNLOCK(descP->accMtx);
+        
+        MLOCK(descP->writeMtx);
+        if (descP->currentWriterP != NULL)
+            socket_down_writer(env, descP, pid);
+        MUNLOCK(descP->writeMtx);
+        
+        MLOCK(descP->readMtx);
+        if (descP->currentReaderP != NULL)
+            socket_down_reader(env, descP, pid);
+        MUNLOCK(descP->readMtx);
+
+    }
+    
+    SSDBG( descP, ("SOCKET", "socket_down -> done\r\n") );
+
+}
 
-        if (compare_pids(env, &descP->currentAcceptor.pid, pid)) {
 
+
+/* *** socket_down_acceptor ***
+ *
+ * Check and then handle a downed acceptor process.
+ *
+ */
+static
+void socket_down_acceptor(ErlNifEnv*        env,
+                          SocketDescriptor* descP,
+                          const ErlNifPid*  pid)
+{
+    if (compare_pids(env, &descP->currentAcceptor.pid, pid)) {
+        
+        SSDBG( descP, ("SOCKET",
+                       "socket_down_acceptor -> "
+                       "current acceptor - try pop the queue\r\n") );
+        
+        if (acceptor_pop(env, descP,
+                         &descP->currentAcceptor.pid,
+                         &descP->currentAcceptor.mon,
+                         &descP->currentAcceptor.ref)) {
+            int res;
+            
+            /* There was another one, so we will still be in accepting state */
+            
             SSDBG( descP, ("SOCKET",
-                           "socket_down -> "
-                           "current acceptor - try pop the queue\r\n") );
+                           "socket_down_acceptor -> new (active) acceptor: "
+                           "\r\n   pid: %T"
+                           "\r\n   ref: %T"
+                           "\r\n",
+                           descP->currentAcceptor.pid,
+                           descP->currentAcceptor.ref) );
             
-            if (acceptor_pop(env, descP,
-                             &descP->currentAcceptor.pid,
-                             &descP->currentAcceptor.mon,
-                             &descP->currentAcceptor.ref)) {
-                int res;
+            if ((res = enif_select(env,
+                                   descP->sock,
+                                   (ERL_NIF_SELECT_READ),
+                                   descP,
+                                   &descP->currentAcceptor.pid,
+                                   descP->currentAcceptor.ref) < 0)) {
                 
-                /* There was another one, so we will still be in accepting state */
+                esock_warning_msg("Failed select (%d) for new acceptor "
+                                  "after current (%T) died\r\n",
+                                  res, *pid);
                 
-                SSDBG( descP, ("SOCKET", "socket_down -> new (active) acceptor: "
-                               "\r\n   pid: %T"
-                               "\r\n   ref: %T"
-                               "\r\n",
-                               descP->currentAcceptor.pid,
-                               descP->currentAcceptor.ref) );
+            }
+            
+        } else {
+            
+            SSDBG( descP, ("SOCKET",
+                           "socket_down_acceptor -> no active acceptor\r\n") );
+            
+            descP->currentAcceptorP = NULL;
+            descP->state            = SOCKET_STATE_LISTENING;
+        }
+        
+    } else {
+        
+        /* Maybe unqueue one of the waiting acceptors */
+        
+        SSDBG( descP, ("SOCKET",
+                       "socket_down_acceptor -> "
+                       "not current acceptor - maybe a waiting acceptor\r\n") );
+        
+        acceptor_unqueue(env, descP, pid);
+    }
+}
+
+
+
+
+/* *** socket_down_writer ***
+ *
+ * Check and then handle a downed writer process.
+ *
+ */
+static
+void socket_down_writer(ErlNifEnv*        env,
+                        SocketDescriptor* descP,
+                        const ErlNifPid*  pid)
+{
+    if (compare_pids(env, &descP->currentWriter.pid, pid)) {
+        
+        SSDBG( descP, ("SOCKET",
+                       "socket_down_writer -> "
+                       "current writer - try pop the queue\r\n") );
+        
+        if (writer_pop(env, descP,
+                       &descP->currentWriter.pid,
+                       &descP->currentWriter.mon,
+                       &descP->currentWriter.ref)) {
+            int res;
+            
+            /* There was another one */
+            
+            SSDBG( descP, ("SOCKET", "socket_down_writer -> new (current) writer: "
+                           "\r\n   pid: %T"
+                           "\r\n   ref: %T"
+                           "\r\n",
+                           descP->currentWriter.pid,
+                           descP->currentWriter.ref) );
+            
+            if ((res = enif_select(env,
+                                   descP->sock,
+                                   (ERL_NIF_SELECT_WRITE),
+                                   descP,
+                                   &descP->currentWriter.pid,
+                                   descP->currentWriter.ref) < 0)) {
                 
-                if ((res = enif_select(env,
-                                       descP->sock,
-                                       (ERL_NIF_SELECT_READ),
-                                       descP,
-                                       &descP->currentAcceptor.pid,
-                                       descP->currentAcceptor.ref) < 0)) {
-                    
-                    esock_warning_msg("Failed select (%d) for new acceptor "
-                                      "after current (%T) died\r\n",
-                                      res, *pid);
-                    
-                }
+                esock_warning_msg("Failed select (%d) for new writer "
+                                  "after current (%T) died\r\n",
+                                  res, *pid);
                 
-            } else {
+            }
+            
+        } else {
+            
+            SSDBG( descP, ("SOCKET",
+                           "socket_down_writer -> no active writer\r\n") );
+            
+            descP->currentWriterP = NULL;
+        }
+        
+    } else {
+        
+        /* Maybe unqueue one of the waiting writer(s) */
+        
+        SSDBG( descP, ("SOCKET",
+                       "socket_down_writer -> "
+                       "not current writer - maybe a waiting writer\r\n") );
+        
+        writer_unqueue(env, descP, pid);
+    }
+}
+
+
+
+
+/* *** socket_down_reader ***
+ *
+ * Check and then handle a downed reader process.
+ *
+ */
+static
+void socket_down_reader(ErlNifEnv*        env,
+                        SocketDescriptor* descP,
+                        const ErlNifPid*  pid)
+{
+    if (compare_pids(env, &descP->currentReader.pid, pid)) {
+        
+        SSDBG( descP, ("SOCKET",
+                       "socket_down_reader -> "
+                       "current reader - try pop the queue\r\n") );
+        
+        if (reader_pop(env, descP,
+                       &descP->currentReader.pid,
+                       &descP->currentReader.mon,
+                       &descP->currentReader.ref)) {
+            int res;
+            
+            /* There was another one */
+            
+            SSDBG( descP, ("SOCKET", "socket_down_reader -> new (current) reader: "
+                           "\r\n   pid: %T"
+                           "\r\n   ref: %T"
+                           "\r\n",
+                           descP->currentReader.pid,
+                           descP->currentReader.ref) );
+            
+            if ((res = enif_select(env,
+                                   descP->sock,
+                                   (ERL_NIF_SELECT_READ),
+                                   descP,
+                                   &descP->currentReader.pid,
+                                   descP->currentReader.ref) < 0)) {
                 
-                SSDBG( descP, ("SOCKET", "socket_down -> no active acceptor\r\n") );
+                esock_warning_msg("Failed select (%d) for new reader "
+                                  "after current (%T) died\r\n",
+                                  res, *pid);
                 
-                descP->currentAcceptorP = NULL;
-                descP->state            = SOCKET_STATE_LISTENING;
             }
             
         } else {
             
-            /* Maybe unqueue one of the waiting acceptors */
-            
             SSDBG( descP, ("SOCKET",
-                           "socket_down -> "
-                           "not current acceptor - maybe a waiting acceptor\r\n") );
+                           "socket_down_reader -> no active reader\r\n") );
             
-            acceptor_unqueue(env, descP, pid);
+            descP->currentReaderP = NULL;
         }
+        
+    } else {
+        
+        /* Maybe unqueue one of the waiting reader(s) */
+        
+        SSDBG( descP, ("SOCKET",
+                       "socket_down_reader -> "
+                       "not current reader - maybe a waiting reader\r\n") );
+        
+        reader_unqueue(env, descP, pid);
     }
-    
-    SSDBG( descP, ("SOCKET", "socket_down -> done\r\n") );
-
 }
 
 
diff --git a/lib/kernel/test/socket_server.erl b/lib/kernel/test/socket_server.erl
index 9142942428..45adffc5e6 100644
--- a/lib/kernel/test/socket_server.erl
+++ b/lib/kernel/test/socket_server.erl
@@ -922,8 +922,8 @@ send(#handler{socket = Sock, msg = true, type = dgram, stimeout = Timeout},
     CMsgHdr  = #{level => ip, type => tos, data => reliability},
     CMsgHdrs = [CMsgHdr],
     MsgHdr   = #{addr => Dest,
-                 iov  => [Msg],
-                 ctrl => CMsgHdrs},
+                 ctrl => CMsgHdrs,
+                 iov  => [Msg]},
     %% ok = socket:setopt(Sock, otp, debug, true),
     Res = socket:sendmsg(Sock, MsgHdr, Timeout),
     %% ok = socket:setopt(Sock, otp, debug, false),