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//===--- Futex Wrapper ------------------------------------------*- 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
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_LIBC_SRC___SUPPORT_THREADS_LINUX_FUTEX_UTILS_H
#define LLVM_LIBC_SRC___SUPPORT_THREADS_LINUX_FUTEX_UTILS_H
#include "src/__support/CPP/atomic.h"
#include "src/__support/CPP/limits.h"
#include "src/__support/CPP/optional.h"
#include "src/__support/OSUtil/syscall.h"
#include "src/__support/macros/attributes.h"
#include "src/__support/macros/config.h"
#include "src/__support/threads/linux/futex_word.h"
#include "src/__support/time/linux/abs_timeout.h"
#include <linux/errno.h>
#include <linux/futex.h>
namespace LIBC_NAMESPACE_DECL {
class Futex : public cpp::Atomic<FutexWordType> {
public:
using Timeout = internal::AbsTimeout;
LIBC_INLINE constexpr Futex(FutexWordType value)
: cpp::Atomic<FutexWordType>(value) {}
LIBC_INLINE Futex &operator=(FutexWordType value) {
cpp::Atomic<FutexWordType>::store(value);
return *this;
}
LIBC_INLINE long wait(FutexWordType expected,
cpp::optional<Timeout> timeout = cpp::nullopt,
bool is_shared = false) {
// use bitset variants to enforce abs_time
uint32_t op = is_shared ? FUTEX_WAIT_BITSET : FUTEX_WAIT_BITSET_PRIVATE;
if (timeout && timeout->is_realtime()) {
op |= FUTEX_CLOCK_REALTIME;
}
for (;;) {
if (this->load(cpp::MemoryOrder::RELAXED) != expected)
return 0;
long ret = syscall_impl<long>(
/* syscall number */ FUTEX_SYSCALL_ID,
/* futex address */ this,
/* futex operation */ op,
/* expected value */ expected,
/* timeout */ timeout ? &timeout->get_timespec() : nullptr,
/* ignored */ nullptr,
/* bitset */ FUTEX_BITSET_MATCH_ANY);
// continue waiting if interrupted; otherwise return the result
// which should normally be 0 or -ETIMEOUT
if (ret == -EINTR)
continue;
return ret;
}
}
LIBC_INLINE long notify_one(bool is_shared = false) {
return syscall_impl<long>(
/* syscall number */ FUTEX_SYSCALL_ID,
/* futex address */ this,
/* futex operation */ is_shared ? FUTEX_WAKE : FUTEX_WAKE_PRIVATE,
/* wake up limit */ 1,
/* ignored */ nullptr,
/* ignored */ nullptr,
/* ignored */ 0);
}
LIBC_INLINE long notify_all(bool is_shared = false) {
return syscall_impl<long>(
/* syscall number */ FUTEX_SYSCALL_ID,
/* futex address */ this,
/* futex operation */ is_shared ? FUTEX_WAKE : FUTEX_WAKE_PRIVATE,
/* wake up limit */ cpp::numeric_limits<int>::max(),
/* ignored */ nullptr,
/* ignored */ nullptr,
/* ignored */ 0);
}
};
static_assert(__is_standard_layout(Futex),
"Futex must be a standard layout type.");
} // namespace LIBC_NAMESPACE_DECL
#endif // LLVM_LIBC_SRC___SUPPORT_THREADS_LINUX_FUTEX_UTILS_H
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