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  1. /*
  2.  * Copyright (C) 2006 Ondrej Palkovsky
  3.  * All rights reserved.
  4.  *
  5.  * Redistribution and use in source and binary forms, with or without
  6.  * modification, are permitted provided that the following conditions
  7.  * are met:
  8.  *
  9.  * - Redistributions of source code must retain the above copyright
  10.  *   notice, this list of conditions and the following disclaimer.
  11.  * - Redistributions in binary form must reproduce the above copyright
  12.  *   notice, this list of conditions and the following disclaimer in the
  13.  *   documentation and/or other materials provided with the distribution.
  14.  * - The name of the author may not be used to endorse or promote products
  15.  *   derived from this software without specific prior written permission.
  16.  *
  17.  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  18.  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  19.  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  20.  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  21.  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  22.  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  23.  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  24.  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25.  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  26.  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27.  */
  28.  
  29. /**
  30.  * Asynchronous library
  31.  *
  32.  * The aim of this library is facilitating writing programs utilizing
  33.  * the asynchronous nature of Helenos IPC, yet using a normal way
  34.  * of programming.
  35.  *
  36.  * You should be able to write very simple multithreaded programs,
  37.  * the async framework will automatically take care of most synchronization
  38.  * problems.
  39.  *
  40.  * Default semantics:
  41.  * - send() - send asynchronously. If the kernel refuses to send more
  42.  *            messages, [ try to get responses from kernel, if nothing
  43.  *            found, might try synchronous ]
  44.  *
  45.  * Example of use:
  46.  *
  47.  * 1) Multithreaded client application
  48.  *  create_thread(thread1);
  49.  *  create_thread(thread2);
  50.  *  ...
  51.  *  
  52.  *  thread1() {
  53.  *        conn = ipc_connect_me_to();
  54.  *        c1 = send(conn);
  55.  *        c2 = send(conn);
  56.  *        wait_for(c1);
  57.  *        wait_for(c2);
  58.  *  }
  59.  *
  60.  *
  61.  * 2) Multithreaded server application
  62.  * main() {
  63.  *      async_manager();
  64.  * }
  65.  *
  66.  *
  67.  * client_connection(icallid, *icall) {
  68.  *       if (want_refuse) {
  69.  *           ipc_answer_fast(icallid, ELIMIT, 0, 0);
  70.  *           return;
  71.  *       }
  72.  *       ipc_answer_fast(icallid, 0, 0, 0);
  73.  *
  74.  *       callid = async_get_call(&call);
  75.  *       handle(callid, call);
  76.  *       ipc_answer_fast(callid, 1,2,3);
  77.  *
  78.  *       callid = async_get_call(&call);
  79.  *       ....
  80.  * }
  81.  *
  82.  * TODO: Detaching/joining dead psthreads?
  83.  */
  84. #include <futex.h>
  85. #include <async.h>
  86. #include <psthread.h>
  87. #include <stdio.h>
  88. #include <libadt/hash_table.h>
  89. #include <libadt/list.h>
  90. #include <ipc/ipc.h>
  91. #include <assert.h>
  92. #include <errno.h>
  93. #include <time.h>
  94. #include <arch/barrier.h>
  95.  
  96. atomic_t async_futex = FUTEX_INITIALIZER;
  97. static hash_table_t conn_hash_table;
  98. static LIST_INITIALIZE(timeout_list);
  99.  
  100. typedef struct {
  101.     pstid_t ptid;                /**< Thread waiting for this message */
  102.     int active;                  /**< If this thread is currently active */
  103.     int done;                    /**< If reply was received */
  104.     ipc_call_t *dataptr;         /**< Pointer where the answer data
  105.                       *   should be stored */
  106.     struct timeval expires;      /**< Expiration time for waiting thread */
  107.     int has_timeout;             /**< If true, this struct is in timeout list */
  108.     link_t link;
  109.  
  110.     ipcarg_t retval;
  111. } amsg_t;
  112.  
  113. typedef struct {
  114.     link_t link;
  115.     ipc_callid_t callid;
  116.     ipc_call_t call;
  117. } msg_t;
  118.  
  119. typedef struct {
  120.     link_t link;
  121.     ipcarg_t in_phone_hash;     /**< Incoming phone hash. */
  122.     link_t msg_queue;              /**< Messages that should be delivered to this thread */
  123.     pstid_t ptid;                /**< Thread associated with this connection */
  124.     int active;                     /**< If this thread is currently active */
  125.     /* Structures for connection opening packet */
  126.     ipc_callid_t callid;
  127.     ipc_call_t call;
  128.     void (*cthread)(ipc_callid_t,ipc_call_t *);
  129. } connection_t;
  130.  
  131.  
  132. __thread connection_t *PS_connection;
  133.  
  134. static void default_client_connection(ipc_callid_t callid, ipc_call_t *call);
  135. static async_client_conn_t client_connection = default_client_connection;
  136.  
  137. /** Add microseconds to give timeval */
  138. static void tv_add(struct timeval *tv, suseconds_t usecs)
  139. {
  140.     tv->tv_sec += usecs / 1000000;
  141.     tv->tv_usec += usecs % 1000000;
  142.     if (tv->tv_usec > 1000000) {
  143.         tv->tv_sec++;
  144.         tv->tv_usec -= 1000000;
  145.     }
  146. }
  147.  
  148. /** Subtract 2 timevals, return microseconds difference */
  149. static suseconds_t tv_sub(struct timeval *tv1, struct timeval *tv2)
  150. {
  151.     suseconds_t result;
  152.  
  153.     result = tv1->tv_usec - tv2->tv_usec;
  154.     result += (tv1->tv_sec - tv2->tv_sec) * 1000000;
  155.  
  156.     return result;
  157. }
  158.  
  159. /** Compare timeval
  160.  *
  161.  * @return 1 if tv1 > tv2, otherwise 0
  162.  */
  163. static int tv_gt(struct timeval *tv1, struct timeval *tv2)
  164. {
  165.     if (tv1->tv_sec > tv2->tv_sec)
  166.         return 1;
  167.     if (tv1->tv_sec == tv2->tv_sec && tv1->tv_usec > tv2->tv_usec)
  168.         return 1;
  169.     return 0;
  170. }
  171. static int tv_gteq(struct timeval *tv1, struct timeval *tv2)
  172. {
  173.     if (tv1->tv_sec > tv2->tv_sec)
  174.         return 1;
  175.     if (tv1->tv_sec == tv2->tv_sec && tv1->tv_usec >= tv2->tv_usec)
  176.         return 1;
  177.     return 0;
  178. }
  179.  
  180. /* Hash table functions */
  181. #define CONN_HASH_TABLE_CHAINS  32
  182.  
  183. static hash_index_t conn_hash(unsigned long *key)
  184. {
  185.     assert(key);
  186.     return ((*key) >> 4) % CONN_HASH_TABLE_CHAINS;
  187. }
  188.  
  189. static int conn_compare(unsigned long key[], hash_count_t keys, link_t *item)
  190. {
  191.     connection_t *hs;
  192.  
  193.     hs = hash_table_get_instance(item, connection_t, link);
  194.    
  195.     return key[0] == hs->in_phone_hash;
  196. }
  197.  
  198. static void conn_remove(link_t *item)
  199. {
  200.     free(hash_table_get_instance(item, connection_t, link));
  201. }
  202.  
  203.  
  204. /** Operations for NS hash table. */
  205. static hash_table_operations_t conn_hash_table_ops = {
  206.     .hash = conn_hash,
  207.     .compare = conn_compare,
  208.     .remove_callback = conn_remove
  209. };
  210.  
  211. /*************************************************/
  212.  
  213. /** Try to route a call to an appropriate connection thread
  214.  *
  215.  */
  216. static int route_call(ipc_callid_t callid, ipc_call_t *call)
  217. {
  218.     connection_t *conn;
  219.     msg_t *msg;
  220.     link_t *hlp;
  221.     unsigned long key;
  222.  
  223.     futex_down(&async_futex);
  224.  
  225.     key = call->in_phone_hash;
  226.     hlp = hash_table_find(&conn_hash_table, &key);
  227.     if (!hlp) {
  228.         futex_up(&async_futex);
  229.         return 0;
  230.     }
  231.     conn = hash_table_get_instance(hlp, connection_t, link);
  232.  
  233.     msg = malloc(sizeof(*msg));
  234.     msg->callid = callid;
  235.     msg->call = *call;
  236.     list_append(&msg->link, &conn->msg_queue);
  237.    
  238.     if (!conn->active) {
  239.         conn->active = 1;
  240.         psthread_add_ready(conn->ptid);
  241.     }
  242.  
  243.     futex_up(&async_futex);
  244.  
  245.     return 1;
  246. }
  247.  
  248. /** Return new incoming message for current(thread-local) connection */
  249. ipc_callid_t async_get_call(ipc_call_t *call)
  250. {
  251.     msg_t *msg;
  252.     ipc_callid_t callid;
  253.    
  254.     assert(PS_connection);
  255.  
  256.     futex_down(&async_futex);
  257.  
  258.     /* If nothing in queue, wait until something appears */
  259.     if (list_empty(&PS_connection->msg_queue)) {
  260.         PS_connection->active = 0;
  261.         psthread_schedule_next_adv(PS_TO_MANAGER);
  262.     }
  263.    
  264.     msg = list_get_instance(PS_connection->msg_queue.next, msg_t, link);
  265.     list_remove(&msg->link);
  266.     callid = msg->callid;
  267.     *call = msg->call;
  268.     free(msg);
  269.    
  270.     futex_up(&async_futex);
  271.     return callid;
  272. }
  273.  
  274. /** Thread function that gets created on new connection
  275.  *
  276.  * This function is defined as a weak symbol - to be redefined in
  277.  * user code.
  278.  */
  279. static void default_client_connection(ipc_callid_t callid, ipc_call_t *call)
  280. {
  281.     ipc_answer_fast(callid, ENOENT, 0, 0);
  282. }
  283.  
  284. /** Function that gets called on interrupt receival
  285.  *
  286.  * This function is defined as a weak symbol - to be redefined in
  287.  * user code.
  288.  */
  289. void interrupt_received(ipc_call_t *call)
  290. {
  291. }
  292.  
  293.  
  294. /** Wrapper for client connection thread
  295.  *
  296.  * When new connection arrives, thread with this function is created.
  297.  * It calls client_connection and does final cleanup.
  298.  *
  299.  * @parameter arg Connection structure pointer
  300.  */
  301. static int connection_thread(void  *arg)
  302. {
  303.     unsigned long key;
  304.     msg_t *msg;
  305.  
  306.     /* Setup thread local connection pointer */
  307.     PS_connection = (connection_t *)arg;
  308.     PS_connection->cthread(PS_connection->callid, &PS_connection->call);
  309.  
  310.     /* Remove myself from connection hash table */
  311.     futex_down(&async_futex);
  312.     key = PS_connection->in_phone_hash;
  313.     hash_table_remove(&conn_hash_table, &key, 1);
  314.     futex_up(&async_futex);
  315.     /* Answer all remaining messages with ehangup */
  316.     while (!list_empty(&PS_connection->msg_queue)) {
  317.         msg = list_get_instance(PS_connection->msg_queue.next, msg_t, link);
  318.         list_remove(&msg->link);
  319.         ipc_answer_fast(msg->callid, EHANGUP, 0, 0);
  320.         free(msg);
  321.     }
  322. }
  323.  
  324. /** Create new thread for a new connection
  325.  *
  326.  * Creates new thread for connection, fills in connection
  327.  * structures and inserts it into the hash table, so that
  328.  * later we can easily do routing of messages to particular
  329.  * threads.
  330.  *
  331.  * @param in_phone_hash Identification of the incoming connection
  332.  * @param callid Callid of the IPC_M_CONNECT_ME_TO packet
  333.  * @param call Call data of the opening packet
  334.  * @param cthread Thread function that should be called upon
  335.  *                opening the connection
  336.  * @return New thread id
  337.  */
  338. pstid_t async_new_connection(ipcarg_t in_phone_hash,ipc_callid_t callid,
  339.                  ipc_call_t *call,
  340.                  void (*cthread)(ipc_callid_t,ipc_call_t *))
  341. {
  342.     pstid_t ptid;
  343.     connection_t *conn;
  344.     unsigned long key;
  345.  
  346.     conn = malloc(sizeof(*conn));
  347.     if (!conn) {
  348.         ipc_answer_fast(callid, ENOMEM, 0, 0);
  349.         return NULL;
  350.     }
  351.     conn->in_phone_hash = in_phone_hash;
  352.     list_initialize(&conn->msg_queue);
  353.     conn->ptid = psthread_create(connection_thread, conn);
  354.     conn->callid = callid;
  355.     if (call)
  356.         conn->call = *call;
  357.     conn->active = 1; /* We will activate it asap */
  358.     conn->cthread = cthread;
  359.     list_initialize(&conn->link);
  360.     if (!conn->ptid) {
  361.         free(conn);
  362.         ipc_answer_fast(callid, ENOMEM, 0, 0);
  363.         return NULL;
  364.     }
  365.     key = conn->in_phone_hash;
  366.     futex_down(&async_futex);
  367.     /* Add connection to hash table */
  368.     hash_table_insert(&conn_hash_table, &key, &conn->link);
  369.     futex_up(&async_futex);
  370.  
  371.     psthread_add_ready(conn->ptid);
  372.  
  373.     return conn->ptid;
  374. }
  375.  
  376. /** Handle call that was received */
  377. static void handle_call(ipc_callid_t callid, ipc_call_t *call)
  378. {
  379.     /* Unrouted call - do some default behaviour */
  380.     switch (IPC_GET_METHOD(*call)) {
  381.     case IPC_M_INTERRUPT:
  382.         interrupt_received(call);
  383.         return;
  384.     case IPC_M_CONNECT_ME_TO:
  385.         /* Open new connection with thread etc. */
  386.         async_new_connection(IPC_GET_ARG3(*call), callid, call, client_connection);
  387.         return;
  388.     }
  389.  
  390.     /* Try to route call through connection tables */
  391.     if (route_call(callid, call))
  392.         return;
  393.  
  394.     /* Unknown call from unknown phone - hang it up */
  395.     ipc_answer_fast(callid, EHANGUP, 0, 0);
  396. }
  397.  
  398. /** Fire all timeouts that expired */
  399. static void handle_expired_timeouts(void)
  400. {
  401.     struct timeval tv;
  402.     amsg_t *amsg;
  403.     link_t *cur;
  404.  
  405.     gettimeofday(&tv,NULL);
  406.     futex_down(&async_futex);
  407.  
  408.     cur = timeout_list.next;
  409.     while (cur != &timeout_list) {
  410.         amsg = list_get_instance(cur,amsg_t,link);
  411.         if (tv_gt(&amsg->expires, &tv))
  412.             break;
  413.         cur = cur->next;
  414.         list_remove(&amsg->link);
  415.         amsg->has_timeout = 0;
  416.         /* Redundant condition? The thread should not
  417.          * be active when it gets here.
  418.          */
  419.         if (!amsg->active) {
  420.             amsg->active = 1;
  421.             psthread_add_ready(amsg->ptid);        
  422.         }
  423.     }
  424.  
  425.     futex_up(&async_futex);
  426. }
  427.  
  428. /** Endless loop dispatching incoming calls and answers */
  429. int async_manager(void)
  430. {
  431.     ipc_call_t call;
  432.     ipc_callid_t callid;
  433.     int timeout;
  434.     amsg_t *amsg;
  435.     struct timeval tv;
  436.  
  437.     while (1) {
  438.         if (psthread_schedule_next_adv(PS_FROM_MANAGER)) {
  439.             futex_up(&async_futex); /* async_futex is always held
  440.                         * when entering manager thread
  441.                         */
  442.             continue;
  443.         }
  444.         futex_down(&async_futex);
  445.         if (!list_empty(&timeout_list)) {
  446.             amsg = list_get_instance(timeout_list.next,amsg_t,link);
  447.             gettimeofday(&tv,NULL);
  448.             if (tv_gteq(&tv, &amsg->expires)) {
  449.                 handle_expired_timeouts();
  450.                 continue;
  451.             } else
  452.                 timeout = tv_sub(&amsg->expires, &tv);
  453.         } else
  454.             timeout = SYNCH_NO_TIMEOUT;
  455.         futex_up(&async_futex);
  456.  
  457.         callid = ipc_wait_cycle(&call, timeout, SYNCH_BLOCKING);
  458.  
  459.         if (!callid) {
  460.             handle_expired_timeouts();
  461.             continue;
  462.         }
  463.  
  464.         if (callid & IPC_CALLID_ANSWERED)
  465.             continue;
  466.  
  467.         handle_call(callid, &call);
  468.     }
  469. }
  470.  
  471. /** Function to start async_manager as a standalone thread
  472.  *
  473.  * When more kernel threads are used, one async manager should
  474.  * exist per thread. The particular implementation may change,
  475.  * currently one async_manager is started automatically per kernel
  476.  * thread except main thread.
  477.  */
  478. static int async_manager_thread(void *arg)
  479. {
  480.     futex_up(&async_futex); /* async_futex is always locked when entering
  481.                 * manager */
  482.     async_manager();
  483. }
  484.  
  485. /** Add one manager to manager list */
  486. void async_create_manager(void)
  487. {
  488.     pstid_t ptid;
  489.  
  490.     ptid = psthread_create(async_manager_thread, NULL);
  491.     psthread_add_manager(ptid);
  492. }
  493.  
  494. /** Remove one manager from manager list */
  495. void async_destroy_manager(void)
  496. {
  497.     psthread_remove_manager();
  498. }
  499.  
  500. /** Initialize internal structures needed for async manager */
  501. int _async_init(void)
  502. {
  503.     if (!hash_table_create(&conn_hash_table, CONN_HASH_TABLE_CHAINS, 1, &conn_hash_table_ops)) {
  504.         printf("%s: cannot create hash table\n", "async");
  505.         return ENOMEM;
  506.     }
  507.    
  508. }
  509.  
  510. /** IPC handler for messages in async framework
  511.  *
  512.  * Notify thread that is waiting for this message, that it arrived
  513.  */
  514. static void reply_received(void *private, int retval,
  515.                ipc_call_t *data)
  516. {
  517.     amsg_t *msg = (amsg_t *) private;
  518.  
  519.     msg->retval = retval;
  520.  
  521.     futex_down(&async_futex);
  522.     /* Copy data after futex_down, just in case the
  523.      * call was detached
  524.      */
  525.     if (msg->dataptr)
  526.         *msg->dataptr = *data;
  527.  
  528.     write_barrier();
  529.     /* Remove message from timeout list */
  530.     if (msg->has_timeout)
  531.         list_remove(&msg->link);
  532.     msg->done = 1;
  533.     if (! msg->active) {
  534.         msg->active = 1;
  535.         psthread_add_ready(msg->ptid);
  536.     }
  537.     futex_up(&async_futex);
  538. }
  539.  
  540. /** Send message and return id of the sent message
  541.  *
  542.  * The return value can be used as input for async_wait() to wait
  543.  * for completion.
  544.  */
  545. aid_t async_send_2(int phoneid, ipcarg_t method, ipcarg_t arg1, ipcarg_t arg2,
  546.            ipc_call_t *dataptr)
  547. {
  548.     amsg_t *msg;
  549.  
  550.     msg = malloc(sizeof(*msg));
  551.     msg->active = 1;
  552.     msg->done = 0;
  553.     msg->dataptr = dataptr;
  554.     ipc_call_async_2(phoneid,method,arg1,arg2,msg,reply_received);
  555.  
  556.     return (aid_t) msg;
  557. }
  558.  
  559. /** Wait for a message sent by async framework
  560.  *
  561.  * @param amsgid Message ID to wait for
  562.  * @param retval Pointer to variable where will be stored retval
  563.  *               of the answered message. If NULL, it is ignored.
  564.  *
  565.  */
  566. void async_wait_for(aid_t amsgid, ipcarg_t *retval)
  567. {
  568.     amsg_t *msg = (amsg_t *) amsgid;
  569.     connection_t *conn;
  570.  
  571.     futex_down(&async_futex);
  572.     if (msg->done) {
  573.         futex_up(&async_futex);
  574.         goto done;
  575.     }
  576.  
  577.     msg->ptid = psthread_get_id();
  578.     msg->active = 0;
  579.     msg->has_timeout = 0;
  580.     /* Leave locked async_futex when entering this function */
  581.     psthread_schedule_next_adv(PS_TO_MANAGER);
  582.     /* futex is up automatically after psthread_schedule_next...*/
  583. done:
  584.     if (retval)
  585.         *retval = msg->retval;
  586.     free(msg);
  587. }
  588.  
  589. /** Insert sort timeout msg into timeouts list
  590.  *
  591.  * Assume async_futex is held
  592.  */
  593. static void insert_timeout(amsg_t *msg)
  594. {
  595.     link_t *tmp;
  596.     amsg_t *cur;
  597.  
  598.     tmp = timeout_list.next;
  599.     while (tmp != &timeout_list) {
  600.         cur = list_get_instance(tmp, amsg_t, link);
  601.         if (tv_gteq(&cur->expires, &msg->expires))
  602.             break;
  603.         tmp = tmp->next;
  604.     }
  605.     list_append(&msg->link, tmp);
  606. }
  607.  
  608. /** Wait for a message sent by async framework with timeout
  609.  *
  610.  * @param amsgid Message ID to wait for
  611.  * @param retval Pointer to variable where will be stored retval
  612.  *               of the answered message. If NULL, it is ignored.
  613.  * @param timeout Timeout in usecs
  614.  * @return 0 on success, ETIMEOUT if timeout expired
  615.  *
  616.  */
  617. int async_wait_timeout(aid_t amsgid, ipcarg_t *retval, suseconds_t timeout)
  618. {
  619.     amsg_t *msg = (amsg_t *) amsgid;
  620.     connection_t *conn;
  621.  
  622.     futex_down(&async_futex);
  623.     if (msg->done) {
  624.         futex_up(&async_futex);
  625.         goto done;
  626.     }
  627.  
  628.     msg->ptid = psthread_get_id();
  629.     msg->active = 0;
  630.     msg->has_timeout = 1;
  631.  
  632.     gettimeofday(&msg->expires, NULL);
  633.     tv_add(&msg->expires, timeout);
  634.     insert_timeout(msg);
  635.  
  636.     /* Leave locked async_futex when entering this function */
  637.     psthread_schedule_next_adv(PS_TO_MANAGER);
  638.     /* futex is up automatically after psthread_schedule_next...*/
  639.  
  640.     if (!msg->done)
  641.         return ETIMEOUT;
  642.  
  643. done:
  644.     if (retval)
  645.         *retval = msg->retval;
  646.     free(msg);
  647.  
  648.     return 0;
  649. }
  650.  
  651. /** Wait specified time, but in the meantime handle incoming events
  652.  *
  653.  * @param timeout Time in microseconds to wait
  654.  */
  655. void async_usleep(suseconds_t timeout)
  656. {
  657.     amsg_t *msg;
  658.    
  659.     msg = malloc(sizeof(*msg));
  660.     if (!msg)
  661.         return;
  662.  
  663.     msg->ptid = psthread_get_id();
  664.     msg->active = 0;
  665.     msg->has_timeout = 1;
  666.  
  667.     gettimeofday(&msg->expires, NULL);
  668.     tv_add(&msg->expires, timeout);
  669.  
  670.     futex_down(&async_futex);
  671.     insert_timeout(msg);
  672.     /* Leave locked async_futex when entering this function */
  673.     psthread_schedule_next_adv(PS_TO_MANAGER);
  674.     /* futex is up automatically after psthread_schedule_next...*/
  675.     free(msg);
  676. }
  677.  
  678. /** Set function that is called, IPC_M_CONNECT_ME_TO is received
  679.  *
  680.  * @param conn Function that will form new psthread.
  681.  */
  682. void async_set_client_connection(async_client_conn_t conn)
  683. {
  684.     client_connection = conn;
  685. }
  686.