sysdeps/unix/sysv/linux/timer_routines.c

   1 /* Copyright (C) 2003-2015 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Ulrich Drepper <drepper@redhat.com>, 2003.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public License as
   7    published by the Free Software Foundation; either version 2.1 of the
   8    License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; see the file COPYING.LIB.  If
  17    not, see <http://www.gnu.org/licenses/>.  */
  18
  19 #include <errno.h>
  20 #include <setjmp.h>
  21 #include <signal.h>
  22 #include <stdbool.h>
  23 #include <sysdep.h>
  24 #include <nptl/pthreadP.h>
  25 #include "kernel-posix-timers.h"
  26
  27
  28 /* List of active SIGEV_THREAD timers.  */
  29 struct timer *__active_timer_sigev_thread;
  30 /* Lock for the __active_timer_sigev_thread.  */
  31 pthread_mutex_t __active_timer_sigev_thread_lock = PTHREAD_MUTEX_INITIALIZER;
  32
  33
  34 struct thread_start_data
  35 {
  36   void (*thrfunc) (sigval_t);
  37   sigval_t sival;
  38 };
  39
  40
  41 /* Helper thread to call the user-provided function.  */
  42 static void *
  43 timer_sigev_thread (void *arg)
  44 {
  45   /* The parent thread has all signals blocked.  This is a bit
  46      surprising for user code, although valid.  We unblock all
  47      signals.  */
  48   sigset_t ss;
  49   sigemptyset (&ss);
  50   INTERNAL_SYSCALL_DECL (err);
  51   INTERNAL_SYSCALL (rt_sigprocmask, err, 4, SIG_SETMASK, &ss, NULL, _NSIG / 8);
  52
  53   struct thread_start_data *td = (struct thread_start_data *) arg;
  54
  55   void (*thrfunc) (sigval_t) = td->thrfunc;
  56   sigval_t sival = td->sival;
  57
  58   /* The TD object was allocated in timer_helper_thread.  */
  59   free (td);
  60
  61   /* Call the user-provided function.  */
  62   thrfunc (sival);
  63
  64   return NULL;
  65 }
  66
  67
  68 /* Helper function to support starting threads for SIGEV_THREAD.  */
  69 static void *
  70 timer_helper_thread (void *arg)
  71 {
  72   /* Wait for the SIGTIMER signal, allowing the setXid signal, and
  73      none else.  */
  74   sigset_t ss;
  75   sigemptyset (&ss);
  76   __sigaddset (&ss, SIGTIMER);
  77
  78   /* Endless loop of waiting for signals.  The loop is only ended when
  79      the thread is canceled.  */
  80   while (1)
  81     {
  82       siginfo_t si;
  83
  84       /* sigwaitinfo cannot be used here, since it deletes
  85          SIGCANCEL == SIGTIMER from the set.  */
  86
  87       int oldtype = LIBC_CANCEL_ASYNC ();
  88
  89       /* XXX The size argument hopefully will have to be changed to the
  90          real size of the user-level sigset_t.  */
  91       int result = INLINE_SYSCALL (rt_sigtimedwait, 4, &ss, &si, NULL,
  92                                    _NSIG / 8);
  93
  94       LIBC_CANCEL_RESET (oldtype);
  95
  96       if (result > 0)
  97         {
  98           if (si.si_code == SI_TIMER)
  99             {
 100               struct timer *tk = (struct timer *) si.si_ptr;
 101
 102               /* Check the timer is still used and will not go away
 103                  while we are reading the values here.  */
 104               pthread_mutex_lock (&__active_timer_sigev_thread_lock);
 105
 106               struct timer *runp = __active_timer_sigev_thread;
 107               while (runp != NULL)
 108                 if (runp == tk)
 109                   break;
 110                 else
 111                   runp = runp->next;
 112
 113               if (runp != NULL)
 114                 {
 115                   struct thread_start_data *td = malloc (sizeof (*td));
 116
 117                   /* There is not much we can do if the allocation fails.  */
 118                   if (td != NULL)
 119                     {
 120                       /* This is the signal we are waiting for.  */
 121                       td->thrfunc = tk->thrfunc;
 122                       td->sival = tk->sival;
 123
 124                       pthread_t th;
 125                       (void) pthread_create (&th, &tk->attr,
 126                                              timer_sigev_thread, td);
 127                     }
 128                 }
 129
 130               pthread_mutex_unlock (&__active_timer_sigev_thread_lock);
 131             }
 132           else if (si.si_code == SI_TKILL)
 133             /* The thread is canceled.  */
 134             pthread_exit (NULL);
 135         }
 136     }
 137 }
 138
 139
 140 /* Control variable for helper thread creation.  */
 141 pthread_once_t __helper_once attribute_hidden;
 142
 143
 144 /* TID of the helper thread.  */
 145 pid_t __helper_tid attribute_hidden;
 146
 147
 148 /* Reset variables so that after a fork a new helper thread gets started.  */
 149 static void
 150 reset_helper_control (void)
 151 {
 152   __helper_once = PTHREAD_ONCE_INIT;
 153   __helper_tid = 0;
 154 }
 155
 156
 157 void
 158 attribute_hidden
 159 __start_helper_thread (void)
 160 {
 161   /* The helper thread needs only very little resources
 162      and should go away automatically when canceled.  */
 163   pthread_attr_t attr;
 164   (void) pthread_attr_init (&attr);
 165   (void) pthread_attr_setstacksize (&attr, __pthread_get_minstack (&attr));
 166
 167   /* Block all signals in the helper thread but SIGSETXID.  To do this
 168      thoroughly we temporarily have to block all signals here.  The
 169      helper can lose wakeups if SIGCANCEL is not blocked throughout,
 170      but sigfillset omits it SIGSETXID.  So, we add SIGCANCEL back
 171      explicitly here.  */
 172   sigset_t ss;
 173   sigset_t oss;
 174   sigfillset (&ss);
 175   __sigaddset (&ss, SIGCANCEL);
 176   INTERNAL_SYSCALL_DECL (err);
 177   INTERNAL_SYSCALL (rt_sigprocmask, err, 4, SIG_SETMASK, &ss, &oss, _NSIG / 8);
 178
 179   /* Create the helper thread for this timer.  */
 180   pthread_t th;
 181   int res = pthread_create (&th, &attr, timer_helper_thread, NULL);
 182   if (res == 0)
 183     /* We managed to start the helper thread.  */
 184     __helper_tid = ((struct pthread *) th)->tid;
 185
 186   /* Restore the signal mask.  */
 187   INTERNAL_SYSCALL (rt_sigprocmask, err, 4, SIG_SETMASK, &oss, NULL,
 188                     _NSIG / 8);
 189
 190   /* No need for the attribute anymore.  */
 191   (void) pthread_attr_destroy (&attr);
 192
 193   /* We have to make sure that after fork()ing a new helper thread can
 194      be created.  */
 195   pthread_atfork (NULL, NULL, reset_helper_control);
 196 }