| 1 | /* Copyright (C) 2002-2022 Free Software Foundation, Inc. |
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| 2 | This file is part of the GNU C Library. |
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| 3 | |
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| 4 | The GNU C Library is free software; you can redistribute it and/or |
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| 5 | modify it under the terms of the GNU Lesser General Public |
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| 6 | License as published by the Free Software Foundation; either |
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| 7 | version 2.1 of the License, or (at your option) any later version. |
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| 8 | |
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| 9 | The GNU C Library is distributed in the hope that it will be useful, |
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| 10 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
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| 11 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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| 12 | Lesser General Public License for more details. |
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| 13 | |
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| 14 | You should have received a copy of the GNU Lesser General Public |
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| 15 | License along with the GNU C Library; if not, see |
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| 16 | <https://www.gnu.org/licenses/>. */ |
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| 17 | |
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| 18 | #include <errno.h> |
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| 19 | #include <shlib-compat.h> |
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| 20 | #include "pthreadP.h" |
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| 21 | #include <stap-probe.h> |
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| 22 | #include <atomic.h> |
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| 23 | #include <futex-internal.h> |
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| 24 | |
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| 25 | #include "pthread_cond_common.c" |
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| 26 | |
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| 27 | /* See __pthread_cond_wait for a high-level description of the algorithm. |
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| 28 | |
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| 29 | A correct program must make sure that no waiters are blocked on the condvar |
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| 30 | when it is destroyed, and that there are no concurrent signals or |
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| 31 | broadcasts. To wake waiters reliably, the program must signal or |
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| 32 | broadcast while holding the mutex or after having held the mutex. It must |
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| 33 | also ensure that no signal or broadcast are still pending to unblock |
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| 34 | waiters; IOW, because waiters can wake up spuriously, the program must |
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| 35 | effectively ensure that destruction happens after the execution of those |
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| 36 | signal or broadcast calls. |
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| 37 | Thus, we can assume that all waiters that are still accessing the condvar |
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| 38 | have been woken. We wait until they have confirmed to have woken up by |
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| 39 | decrementing __wrefs. */ |
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| 40 | int |
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| 41 | __pthread_cond_destroy (pthread_cond_t *cond) |
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| 42 | { |
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| 43 | LIBC_PROBE (cond_destroy, 1, cond); |
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| 44 | |
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| 45 | /* Set the wake request flag. We could also spin, but destruction that is |
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| 46 | concurrent with still-active waiters is probably neither common nor |
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| 47 | performance critical. Acquire MO to synchronize with waiters confirming |
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| 48 | that they finished. */ |
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| 49 | unsigned int wrefs = atomic_fetch_or_acquire (&cond->__data.__wrefs, 4); |
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| 50 | int private = __condvar_get_private (flags: wrefs); |
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| 51 | while (wrefs >> 3 != 0) |
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| 52 | { |
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| 53 | futex_wait_simple (futex_word: &cond->__data.__wrefs, expected: wrefs, private); |
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| 54 | /* See above. */ |
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| 55 | wrefs = atomic_load_acquire (&cond->__data.__wrefs); |
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| 56 | } |
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| 57 | /* The memory the condvar occupies can now be reused. */ |
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| 58 | return 0; |
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| 59 | } |
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| 60 | libc_hidden_def (__pthread_cond_destroy) |
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| 61 | versioned_symbol (libc, __pthread_cond_destroy, |
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| 62 | pthread_cond_destroy, GLIBC_2_3_2); |
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| 63 | |
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