1/* Common definition for pthread_{timed,try}join{_np}.
2 Copyright (C) 2017-2020 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
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
7 License as published by the Free Software Foundation; either
8 version 2.1 of the 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; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19#include "pthreadP.h"
20#include <atomic.h>
21#include <stap-probe.h>
22#include <time.h>
23
24static void
25cleanup (void *arg)
26{
27 /* If we already changed the waiter ID, reset it. The call cannot
28 fail for any reason but the thread not having done that yet so
29 there is no reason for a loop. */
30 struct pthread *self = THREAD_SELF;
31 atomic_compare_exchange_weak_acquire (&arg, &self, NULL);
32}
33
34/* The kernel notifies a process which uses CLONE_CHILD_CLEARTID via futex
35 wake-up when the clone terminates. The memory location contains the
36 thread ID while the clone is running and is reset to zero by the kernel
37 afterwards. The kernel up to version 3.16.3 does not use the private futex
38 operations for futex wake-up when the clone terminates. */
39static int
40clockwait_tid (pid_t *tidp, clockid_t clockid, const struct timespec *abstime)
41{
42 pid_t tid;
43
44 if (! valid_nanoseconds (abstime->tv_nsec))
45 return EINVAL;
46
47 /* Repeat until thread terminated. */
48 while ((tid = *tidp) != 0)
49 {
50 struct timespec rt;
51
52 /* Get the current time. This can only fail if clockid is
53 invalid. */
54 if (__glibc_unlikely (__clock_gettime (clockid, &rt)))
55 return EINVAL;
56
57 /* Compute relative timeout. */
58 rt.tv_sec = abstime->tv_sec - rt.tv_sec;
59 rt.tv_nsec = abstime->tv_nsec - rt.tv_nsec;
60 if (rt.tv_nsec < 0)
61 {
62 rt.tv_nsec += 1000000000;
63 --rt.tv_sec;
64 }
65
66 /* Already timed out? */
67 if (rt.tv_sec < 0)
68 return ETIMEDOUT;
69
70 /* If *tidp == tid, wait until thread terminates or the wait times out.
71 The kernel up to version 3.16.3 does not use the private futex
72 operations for futex wake-up when the clone terminates. */
73 if (lll_futex_timed_wait_cancel (tidp, tid, &rt, LLL_SHARED)
74 == -ETIMEDOUT)
75 return ETIMEDOUT;
76 }
77
78 return 0;
79}
80
81int
82__pthread_clockjoin_ex (pthread_t threadid, void **thread_return,
83 clockid_t clockid,
84 const struct timespec *abstime, bool block)
85{
86 struct pthread *pd = (struct pthread *) threadid;
87
88 /* Make sure the descriptor is valid. */
89 if (INVALID_NOT_TERMINATED_TD_P (pd))
90 /* Not a valid thread handle. */
91 return ESRCH;
92
93 /* Is the thread joinable?. */
94 if (IS_DETACHED (pd))
95 /* We cannot wait for the thread. */
96 return EINVAL;
97
98 struct pthread *self = THREAD_SELF;
99 int result = 0;
100
101 LIBC_PROBE (pthread_join, 1, threadid);
102
103 if ((pd == self
104 || (self->joinid == pd
105 && (pd->cancelhandling
106 & (CANCELING_BITMASK | CANCELED_BITMASK | EXITING_BITMASK
107 | TERMINATED_BITMASK)) == 0))
108 && !CANCEL_ENABLED_AND_CANCELED (self->cancelhandling))
109 /* This is a deadlock situation. The threads are waiting for each
110 other to finish. Note that this is a "may" error. To be 100%
111 sure we catch this error we would have to lock the data
112 structures but it is not necessary. In the unlikely case that
113 two threads are really caught in this situation they will
114 deadlock. It is the programmer's problem to figure this
115 out. */
116 return EDEADLK;
117
118 /* Wait for the thread to finish. If it is already locked something
119 is wrong. There can only be one waiter. */
120 else if (__glibc_unlikely (atomic_compare_exchange_weak_acquire (&pd->joinid,
121 &self,
122 NULL)))
123 /* There is already somebody waiting for the thread. */
124 return EINVAL;
125
126 /* BLOCK waits either indefinitely or based on an absolute time. POSIX also
127 states a cancellation point shall occur for pthread_join, and we use the
128 same rationale for posix_timedjoin_np. Both clockwait_tid and the futex
129 call use the cancellable variant. */
130 if (block)
131 {
132 /* During the wait we change to asynchronous cancellation. If we
133 are cancelled the thread we are waiting for must be marked as
134 un-wait-ed for again. */
135 pthread_cleanup_push (cleanup, &pd->joinid);
136
137 if (abstime != NULL)
138 result = clockwait_tid (&pd->tid, clockid, abstime);
139 else
140 {
141 pid_t tid;
142 /* We need acquire MO here so that we synchronize with the
143 kernel's store to 0 when the clone terminates. (see above) */
144 while ((tid = atomic_load_acquire (&pd->tid)) != 0)
145 lll_futex_wait_cancel (&pd->tid, tid, LLL_SHARED);
146 }
147
148 pthread_cleanup_pop (0);
149 }
150
151 void *pd_result = pd->result;
152 if (__glibc_likely (result == 0))
153 {
154 /* We mark the thread as terminated and as joined. */
155 pd->tid = -1;
156
157 /* Store the return value if the caller is interested. */
158 if (thread_return != NULL)
159 *thread_return = pd_result;
160
161 /* Free the TCB. */
162 __free_tcb (pd);
163 }
164 else
165 pd->joinid = NULL;
166
167 LIBC_PROBE (pthread_join_ret, 3, threadid, result, pd_result);
168
169 return result;
170}
171