resolv/gai_notify.c

   1 /* Copyright (C) 2001-2022 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <netdb.h>
  19 #include <pthread.h>
  20 #include <stdlib.h>
  21 #include <gai_misc.h>
  22
  23 #if !PTHREAD_IN_LIBC
  24 /* The available function names differ outside of libc.  (In libc, we
  25    need to use hidden aliases to avoid the PLT.)  */
  26 #define __pthread_attr_init pthread_attr_init
  27 #define __pthread_attr_setdetachstate pthread_attr_setdetachstate
  28 #define __pthread_cond_signal pthread_cond_signal
  29 #define __pthread_cond_timedwait pthread_cond_timedwait
  30 #define __pthread_create pthread_create
  31 #endif
  32
  33 struct notify_func
  34   {
  35     void (*func) (sigval_t);
  36     sigval_t value;
  37   };
  38
  39 static void *
  40 notify_func_wrapper (void *arg)
  41 {
  42   gai_start_notify_thread ();
  43   struct notify_func *const n = arg;
  44   void (*func) (sigval_t) = n->func;
  45   sigval_t value = n->value;
  46   free (n);
  47   (*func) (value);
  48   return NULL;
  49 }
  50
  51
  52 int
  53 __gai_notify_only (struct sigevent *sigev, pid_t caller_pid)
  54 {
  55   int result = 0;
  56
  57   /* Send the signal to notify about finished processing of the request.  */
  58   if (sigev->sigev_notify == SIGEV_THREAD)
  59     {
  60       /* We have to start a thread.  */
  61       pthread_t tid;
  62       pthread_attr_t attr, *pattr;
  63
  64       pattr = (pthread_attr_t *) sigev->sigev_notify_attributes;
  65       if (pattr == NULL)
  66         {
  67           __pthread_attr_init (&attr);
  68           __pthread_attr_setdetachstate (&attr, PTHREAD_CREATE_DETACHED);
  69           pattr = &attr;
  70         }
  71
  72       /* SIGEV may be freed as soon as we return, so we cannot let the
  73          notification thread use that pointer.  Even though a sigval_t is
  74          only one word and the same size as a void *, we cannot just pass
  75          the value through pthread_create as the argument and have the new
  76          thread run the user's function directly, because on some machines
  77          the calling convention for a union like sigval_t is different from
  78          that for a pointer type like void *.  */
  79       struct notify_func *nf = malloc (sizeof *nf);
  80       if (nf == NULL)
  81         result = -1;
  82       else
  83         {
  84           nf->func = sigev->sigev_notify_function;
  85           nf->value = sigev->sigev_value;
  86           if (__pthread_create (&tid, pattr, notify_func_wrapper, nf) < 0)
  87             {
  88               free (nf);
  89               result = -1;
  90             }
  91         }
  92     }
  93   else if (sigev->sigev_notify == SIGEV_SIGNAL)
  94     /* We have to send a signal.  */
  95     if (__gai_sigqueue (sigev->sigev_signo, sigev->sigev_value, caller_pid)
  96         < 0)
  97       result = -1;
  98
  99   return result;
 100 }
 101
 102
 103 void
 104 __gai_notify (struct requestlist *req)
 105 {
 106   struct waitlist *waitlist;
 107
 108   /* Now also notify possibly waiting threads.  */
 109   waitlist = req->waiting;
 110   while (waitlist != NULL)
 111     {
 112       struct waitlist *next = waitlist->next;
 113
 114       if (waitlist->sigevp == NULL)
 115         {
 116 #ifdef DONT_NEED_GAI_MISC_COND
 117           GAI_MISC_NOTIFY (waitlist);
 118 #else
 119           /* Decrement the counter.  */
 120           --*waitlist->counterp;
 121
 122           pthread_cond_signal (waitlist->cond);
 123 #endif
 124         }
 125       else
 126         /* This is part of an asynchronous `getaddrinfo_a' operation.  If
 127            this request is the last one, send the signal.  */
 128         if (--*waitlist->counterp == 0)
 129           {
 130             __gai_notify_only (waitlist->sigevp, waitlist->caller_pid);
 131             /* This is tricky.  See getaddrinfo_a.c for the reason why
 132                this works.  */
 133             free ((void *) waitlist->counterp);
 134           }
 135
 136       waitlist = next;
 137     }
 138 }