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      1 /*
      2  * Copyright (C) 2008 The Android Open Source Project
      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  *  * Redistributions of source code must retain the above copyright
      9  *    notice, this list of conditions and the following disclaimer.
     10  *  * Redistributions in binary form must reproduce the above copyright
     11  *    notice, this list of conditions and the following disclaimer in
     12  *    the documentation and/or other materials provided with the
     13  *    distribution.
     14  *
     15  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
     16  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
     17  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
     18  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
     19  * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
     20  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
     21  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
     22  * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
     23  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
     24  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
     25  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     26  * SUCH DAMAGE.
     27  */
     28 
     29 #include "private/kernel_sigset_t.h"
     30 
     31 #include <errno.h>
     32 #include <malloc.h>
     33 #include <pthread.h>
     34 #include <stdatomic.h>
     35 #include <stdio.h>
     36 #include <string.h>
     37 #include <time.h>
     38 
     39 // System calls.
     40 extern "C" int __rt_sigtimedwait(const sigset_t*, siginfo_t*, const timespec*, size_t);
     41 extern "C" int __timer_create(clockid_t, sigevent*, __kernel_timer_t*);
     42 extern "C" int __timer_delete(__kernel_timer_t);
     43 extern "C" int __timer_getoverrun(__kernel_timer_t);
     44 extern "C" int __timer_gettime(__kernel_timer_t, itimerspec*);
     45 extern "C" int __timer_settime(__kernel_timer_t, int, const itimerspec*, itimerspec*);
     46 
     47 // Most POSIX timers are handled directly by the kernel. We translate SIGEV_THREAD timers
     48 // into SIGEV_THREAD_ID timers so the kernel handles all the time-related stuff and we just
     49 // need to worry about running user code on a thread.
     50 
     51 // We can't use SIGALRM because too many other C library functions throw that around, and since
     52 // they don't send to a specific thread, all threads are eligible to handle the signal and we can
     53 // end up with one of our POSIX timer threads handling it (meaning that the intended recipient
     54 // doesn't). glibc uses SIGRTMIN for its POSIX timer implementation, so in the absence of any
     55 // reason to use anything else, we use that too.
     56 static const int TIMER_SIGNAL = (__SIGRTMIN + 0);
     57 
     58 struct PosixTimer {
     59   __kernel_timer_t kernel_timer_id;
     60 
     61   int sigev_notify;
     62 
     63   // The fields below are only needed for a SIGEV_THREAD timer.
     64   pthread_t callback_thread;
     65   void (*callback)(sigval_t);
     66   sigval_t callback_argument;
     67   atomic_bool deleted;  // Set when the timer is deleted, to prevent further calling of callback.
     68 };
     69 
     70 static __kernel_timer_t to_kernel_timer_id(timer_t timer) {
     71   return reinterpret_cast<PosixTimer*>(timer)->kernel_timer_id;
     72 }
     73 
     74 static void* __timer_thread_start(void* arg) {
     75   PosixTimer* timer = reinterpret_cast<PosixTimer*>(arg);
     76 
     77   kernel_sigset_t sigset;
     78   sigaddset(sigset.get(), TIMER_SIGNAL);
     79 
     80   while (true) {
     81     // Wait for a signal...
     82     siginfo_t si;
     83     memset(&si, 0, sizeof(si));
     84     int rc = __rt_sigtimedwait(sigset.get(), &si, NULL, sizeof(sigset));
     85     if (rc == -1) {
     86       continue;
     87     }
     88 
     89     if (si.si_code == SI_TIMER) {
     90       // This signal was sent because a timer fired, so call the callback.
     91 
     92       // All events to the callback will be ignored when the timer is deleted.
     93       if (atomic_load(&timer->deleted) == true) {
     94         continue;
     95       }
     96       timer->callback(timer->callback_argument);
     97     } else if (si.si_code == SI_TKILL) {
     98       // This signal was sent because someone wants us to exit.
     99       free(timer);
    100       return NULL;
    101     }
    102   }
    103 }
    104 
    105 static void __timer_thread_stop(PosixTimer* timer) {
    106   atomic_store(&timer->deleted, true);
    107   pthread_kill(timer->callback_thread, TIMER_SIGNAL);
    108 }
    109 
    110 // http://pubs.opengroup.org/onlinepubs/9699919799/functions/timer_create.html
    111 int timer_create(clockid_t clock_id, sigevent* evp, timer_t* timer_id) {
    112   PosixTimer* timer = reinterpret_cast<PosixTimer*>(malloc(sizeof(PosixTimer)));
    113   if (timer == NULL) {
    114     return -1;
    115   }
    116 
    117   timer->sigev_notify = (evp == NULL) ? SIGEV_SIGNAL : evp->sigev_notify;
    118 
    119   // If not a SIGEV_THREAD timer, the kernel can handle it without our help.
    120   if (timer->sigev_notify != SIGEV_THREAD) {
    121     if (__timer_create(clock_id, evp, &timer->kernel_timer_id) == -1) {
    122       free(timer);
    123       return -1;
    124     }
    125 
    126     *timer_id = timer;
    127     return 0;
    128   }
    129 
    130   // Otherwise, this must be SIGEV_THREAD timer...
    131   timer->callback = evp->sigev_notify_function;
    132   timer->callback_argument = evp->sigev_value;
    133   atomic_init(&timer->deleted, false);
    134 
    135   // Check arguments that the kernel doesn't care about but we do.
    136   if (timer->callback == NULL) {
    137     free(timer);
    138     errno = EINVAL;
    139     return -1;
    140   }
    141 
    142   // Create this timer's thread.
    143   pthread_attr_t thread_attributes;
    144   if (evp->sigev_notify_attributes == NULL) {
    145     pthread_attr_init(&thread_attributes);
    146   } else {
    147     thread_attributes = *reinterpret_cast<pthread_attr_t*>(evp->sigev_notify_attributes);
    148   }
    149   pthread_attr_setdetachstate(&thread_attributes, PTHREAD_CREATE_DETACHED);
    150 
    151   // We start the thread with TIMER_SIGNAL blocked by blocking the signal here and letting it
    152   // inherit. If it tried to block the signal itself, there would be a race.
    153   kernel_sigset_t sigset;
    154   sigaddset(sigset.get(), TIMER_SIGNAL);
    155   kernel_sigset_t old_sigset;
    156   pthread_sigmask(SIG_BLOCK, sigset.get(), old_sigset.get());
    157 
    158   int rc = pthread_create(&timer->callback_thread, &thread_attributes, __timer_thread_start, timer);
    159 
    160   pthread_sigmask(SIG_SETMASK, old_sigset.get(), NULL);
    161 
    162   if (rc != 0) {
    163     free(timer);
    164     errno = rc;
    165     return -1;
    166   }
    167 
    168   sigevent se = *evp;
    169   se.sigev_signo = TIMER_SIGNAL;
    170   se.sigev_notify = SIGEV_THREAD_ID;
    171   se.sigev_notify_thread_id = pthread_gettid_np(timer->callback_thread);
    172   if (__timer_create(clock_id, &se, &timer->kernel_timer_id) == -1) {
    173     __timer_thread_stop(timer);
    174     return -1;
    175   }
    176 
    177   // Give the thread a specific meaningful name.
    178   // It can't do this itself because the kernel timer isn't created until after it's running.
    179   char name[16]; // 16 is the kernel-imposed limit.
    180   snprintf(name, sizeof(name), "POSIX timer %d", to_kernel_timer_id(timer));
    181   pthread_setname_np(timer->callback_thread, name);
    182 
    183   *timer_id = timer;
    184   return 0;
    185 }
    186 
    187 // http://pubs.opengroup.org/onlinepubs/9699919799/functions/timer_delete.html
    188 int timer_delete(timer_t id) {
    189   int rc = __timer_delete(to_kernel_timer_id(id));
    190   if (rc == -1) {
    191     return -1;
    192   }
    193 
    194   PosixTimer* timer = reinterpret_cast<PosixTimer*>(id);
    195   if (timer->sigev_notify == SIGEV_THREAD) {
    196     // Stopping the timer's thread frees the timer data when it's safe.
    197     __timer_thread_stop(timer);
    198   } else {
    199     // For timers without threads, we can just free right away.
    200     free(timer);
    201   }
    202 
    203   return 0;
    204 }
    205 
    206 // http://pubs.opengroup.org/onlinepubs/9699919799/functions/timer_gettime.html
    207 int timer_gettime(timer_t id, itimerspec* ts) {
    208   return __timer_gettime(to_kernel_timer_id(id), ts);
    209 }
    210 
    211 // http://pubs.opengroup.org/onlinepubs/9699919799/functions/timer_settime.html
    212 // When using timer_settime to disarm a repeatable SIGEV_THREAD timer with a very small
    213 // period (like below 1ms), the kernel may continue to send events to the callback thread
    214 // for a few extra times. This behavior is fine because in POSIX standard: The effect of
    215 // disarming or resetting a timer with pending expiration notifications is unspecified.
    216 int timer_settime(timer_t id, int flags, const itimerspec* ts, itimerspec* ots) {
    217   PosixTimer* timer= reinterpret_cast<PosixTimer*>(id);
    218   return __timer_settime(timer->kernel_timer_id, flags, ts, ots);
    219 }
    220 
    221 // http://pubs.opengroup.org/onlinepubs/9699919799/functions/timer_getoverrun.html
    222 int timer_getoverrun(timer_t id) {
    223   return __timer_getoverrun(to_kernel_timer_id(id));
    224 }
    225