| 1 | //===-- Linux implementation of the callonce function ---------------------===// |
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| 2 | // |
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| 3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
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| 4 | // See https://llvm.org/LICENSE.txt for license information. |
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| 5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
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| 6 | // |
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| 7 | //===----------------------------------------------------------------------===// |
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| 8 | |
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| 9 | #include "src/__support/threads/callonce.h" |
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| 10 | #include "src/__support/macros/config.h" |
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| 11 | #include "src/__support/threads/linux/callonce.h" |
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| 12 | #include "src/__support/threads/linux/futex_utils.h" |
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| 13 | |
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| 14 | namespace LIBC_NAMESPACE_DECL { |
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| 15 | namespace callonce_impl { |
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| 16 | int callonce_slowpath(CallOnceFlag *flag, CallOnceCallback *func) { |
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| 17 | auto *futex_word = reinterpret_cast<Futex *>(flag); |
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| 18 | |
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| 19 | FutexWordType not_called = NOT_CALLED; |
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| 20 | |
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| 21 | // The call_once call can return only after the called function |func| |
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| 22 | // returns. So, we use futexes to synchronize calls with the same flag value. |
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| 23 | if (futex_word->compare_exchange_strong(not_called, START)) { |
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| 24 | func(); |
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| 25 | auto status = futex_word->exchange(FINISH); |
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| 26 | if (status == WAITING) |
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| 27 | futex_word->notify_all(); |
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| 28 | return 0; |
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| 29 | } |
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| 30 | |
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| 31 | FutexWordType status = START; |
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| 32 | if (futex_word->compare_exchange_strong(status, WAITING) || |
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| 33 | status == WAITING) { |
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| 34 | futex_word->wait(WAITING); |
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| 35 | } |
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| 36 | |
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| 37 | return 0; |
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| 38 | } |
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| 39 | } // namespace callonce_impl |
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| 40 | } // namespace LIBC_NAMESPACE_DECL |
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| 41 | |
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