1/* Common definition for pthread_{timed,try}join{_np}.
2 Copyright (C) 2017-2024 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#include <futex-internal.h>
24
25static void
26cleanup (void *arg)
27{
28 /* If we already changed the waiter ID, reset it. The call cannot
29 fail for any reason but the thread not having done that yet so
30 there is no reason for a loop. */
31 struct pthread *self = THREAD_SELF;
32 atomic_compare_exchange_weak_acquire (&arg, &self, NULL);
33}
34
35int
36__pthread_clockjoin_ex (pthread_t threadid, void **thread_return,
37 clockid_t clockid,
38 const struct __timespec64 *abstime, bool block)
39{
40 struct pthread *pd = (struct pthread *) threadid;
41
42 /* Make sure the descriptor is valid. */
43 if (INVALID_NOT_TERMINATED_TD_P (pd))
44 /* Not a valid thread handle. */
45 return ESRCH;
46
47 /* Is the thread joinable?. */
48 if (IS_DETACHED (pd))
49 /* We cannot wait for the thread. */
50 return EINVAL;
51
52 struct pthread *self = THREAD_SELF;
53 int result = 0;
54
55 LIBC_PROBE (pthread_join, 1, threadid);
56
57 if ((pd == self
58 || (self->joinid == pd
59 && (pd->cancelhandling
60 & (CANCELING_BITMASK | CANCELED_BITMASK | EXITING_BITMASK
61 | TERMINATED_BITMASK)) == 0))
62 && !cancel_enabled_and_canceled (value: self->cancelhandling))
63 /* This is a deadlock situation. The threads are waiting for each
64 other to finish. Note that this is a "may" error. To be 100%
65 sure we catch this error we would have to lock the data
66 structures but it is not necessary. In the unlikely case that
67 two threads are really caught in this situation they will
68 deadlock. It is the programmer's problem to figure this
69 out. */
70 return EDEADLK;
71
72 /* Wait for the thread to finish. If it is already locked something
73 is wrong. There can only be one waiter. */
74 else if (__glibc_unlikely (atomic_compare_exchange_weak_acquire (&pd->joinid,
75 &self,
76 NULL)))
77 /* There is already somebody waiting for the thread. */
78 return EINVAL;
79
80 /* BLOCK waits either indefinitely or based on an absolute time. POSIX also
81 states a cancellation point shall occur for pthread_join, and we use the
82 same rationale for posix_timedjoin_np. Both clockwait_tid and the futex
83 call use the cancellable variant. */
84 if (block)
85 {
86 /* During the wait we change to asynchronous cancellation. If we
87 are cancelled the thread we are waiting for must be marked as
88 un-wait-ed for again. */
89 pthread_cleanup_push (cleanup, &pd->joinid);
90
91 /* We need acquire MO here so that we synchronize with the
92 kernel's store to 0 when the clone terminates. (see above) */
93 pid_t tid;
94 while ((tid = atomic_load_acquire (&pd->tid)) != 0)
95 {
96 /* The kernel notifies a process which uses CLONE_CHILD_CLEARTID via
97 futex wake-up when the clone terminates. The memory location
98 contains the thread ID while the clone is running and is reset to
99 zero by the kernel afterwards. The kernel up to version 3.16.3
100 does not use the private futex operations for futex wake-up when
101 the clone terminates. */
102 int ret = __futex_abstimed_wait_cancelable64 (
103 (unsigned int *) &pd->tid, tid, clockid, abstime, LLL_SHARED);
104 if (ret == ETIMEDOUT || ret == EOVERFLOW)
105 {
106 result = ret;
107 break;
108 }
109 }
110
111 pthread_cleanup_pop (0);
112 }
113
114 void *pd_result = pd->result;
115 if (__glibc_likely (result == 0))
116 {
117 /* We mark the thread as terminated and as joined. */
118 pd->tid = -1;
119
120 /* Store the return value if the caller is interested. */
121 if (thread_return != NULL)
122 *thread_return = pd_result;
123
124 /* Free the TCB. */
125 __nptl_free_tcb (pd);
126 }
127 else
128 pd->joinid = NULL;
129
130 LIBC_PROBE (pthread_join_ret, 3, threadid, result, pd_result);
131
132 return result;
133}
134

source code of glibc/nptl/pthread_join_common.c