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 struct 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 
to_kernel_timer_id(timer_t timer)70 static __kernel_timer_t to_kernel_timer_id(timer_t timer) {
71   return reinterpret_cast<PosixTimer*>(timer)->kernel_timer_id;
72 }
73 
__timer_thread_start(void * arg)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 
__timer_thread_stop(PosixTimer * timer)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
timer_create(clockid_t clock_id,sigevent * evp,timer_t * timer_id)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
timer_delete(timer_t id)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
timer_gettime(timer_t id,itimerspec * ts)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.
timer_settime(timer_t id,int flags,const itimerspec * ts,itimerspec * ots)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
timer_getoverrun(timer_t id)222 int timer_getoverrun(timer_t id) {
223   return __timer_getoverrun(to_kernel_timer_id(id));
224 }
225