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[libc] remove redundant call_once (#79226)

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Missed cleanup from https://reviews.llvm.org/D134716.

Fixes: #79220
This commit is contained in:
Nick Desaulniers 2024-01-23 15:38:12 -08:00 committed by GitHub
parent 22da809602
commit 6a3ace20c8
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2 changed files with 0 additions and 78 deletions
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67
libc/src/threads/linux/call_once.cpp
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@ -1,67 +0,0 @@
//===-- Linux implementation of the call_once function --------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "Futex.h"
#include "src/__support/CPP/atomic.h"
#include "src/__support/OSUtil/syscall.h" // For syscall functions.
#include "src/__support/common.h"
#include "src/threads/call_once.h"
#include "src/threads/linux/Futex.h"
#include <limits.h>
#include <linux/futex.h>
#include <sys/syscall.h> // For syscall numbers.
#include <threads.h> // For call_once related type definition.
namespace LIBC_NAMESPACE {
static constexpr FutexWordType START = 0x11;
static constexpr FutexWordType WAITING = 0x22;
static constexpr FutexWordType FINISH = 0x33;
static constexpr once_flag ONCE_FLAG_INIT_VAL = ONCE_FLAG_INIT;
LLVM_LIBC_FUNCTION(void, call_once,
(once_flag * flag, __call_once_func_t func)) {
auto *futex_word = reinterpret_cast<cpp::Atomic<FutexWordType> *>(flag);
static_assert(sizeof(*futex_word) == sizeof(once_flag));
FutexWordType not_called = ONCE_FLAG_INIT_VAL.__word;
// The C standard wording says:
//
// The completion of the function func synchronizes with all
// previous or subsequent calls to call_once with the same
// flag variable.
//
// What this means is that, the call_once call can return only after
// the called function |func| returns. So, we use futexes to synchronize
// calls with the same flag value.
if (futex_word->compare_exchange_strong(not_called, START)) {
func();
auto status = futex_word->exchange(FINISH);
if (status == WAITING) {
LIBC_NAMESPACE::syscall_impl(FUTEX_SYSCALL_ID, &futex_word->val,
FUTEX_WAKE_PRIVATE,
INT_MAX, // Wake all waiters.
0, 0, 0);
}
return;
}
FutexWordType status = START;
if (futex_word->compare_exchange_strong(status, WAITING) ||
status == WAITING) {
LIBC_NAMESPACE::syscall_impl(
FUTEX_SYSCALL_ID, &futex_word->val, FUTEX_WAIT_PRIVATE,
WAITING, // Block only if status is still |WAITING|.
0, 0, 0);
}
}
} // namespace LIBC_NAMESPACE

11
libc/src/threads/linux/thread_start_args.h.def
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@ -1,11 +0,0 @@
//===-- Implementation of the get_start_args_addr function ------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include <stdint.h>
%%include_file(${thread_start_args})