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.
40extern "C" int __rt_sigtimedwait(const sigset_t*, siginfo_t*, const struct timespec*, size_t);
41extern "C" int __timer_create(clockid_t, sigevent*, __kernel_timer_t*);
42extern "C" int __timer_delete(__kernel_timer_t);
43extern "C" int __timer_getoverrun(__kernel_timer_t);
44extern "C" int __timer_gettime(__kernel_timer_t, itimerspec*);
45extern "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.
56static const int TIMER_SIGNAL = (__SIGRTMIN + 0);
57
58struct 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
70static __kernel_timer_t to_kernel_timer_id(timer_t timer) {
71  return reinterpret_cast<PosixTimer*>(timer)->kernel_timer_id;
72}
73
74static 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
105static 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
111int 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
188int 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
207int 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.
216int 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
222int timer_getoverrun(timer_t id) {
223  return __timer_getoverrun(to_kernel_timer_id(id));
224}
225