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aa0265b03e
`gettid` wrapper was added in glibc 2.30, and Ubuntu 18.04 uses glibc 2.27, so use raw syscall instead of it.
95 lines
2.7 KiB
C++
95 lines
2.7 KiB
C++
//==--- ulock.h - 32-bit futex-based lock for Linux ------------ -*-C++ -*-===//
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//
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// This source file is part of the Swift.org open source project
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//
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// Copyright (c) 2022 Apple Inc. and the Swift project authors
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// Licensed under Apache License v2.0 with Runtime Library Exception
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//
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// See https://swift.org/LICENSE.txt for license information
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// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
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//
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//===----------------------------------------------------------------------===//
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//
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// Implements a 32-bit futex-based locking primitive with priority inversion
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// support.
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//
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// This has comparable performance to pthread_mutex_t (on x86-64, it's slower
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// under contention, but not much different otherwise; other architectures may
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// vary), but it only takes up 32 bits instead of 40 *bytes*.
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//
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//===----------------------------------------------------------------------===//
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#ifndef SWIFT_THREADING_IMPL_LINUX_ULOCK_H
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#define SWIFT_THREADING_IMPL_LINUX_ULOCK_H
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// This file is specific to Linux; we're just going to assume we can use
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// various GCC/Clang extensions here.
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#include <linux/futex.h>
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#include <sys/syscall.h>
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#include <sys/time.h>
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#include <sys/types.h>
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#include <unistd.h>
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#include <atomic>
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#include <cstdint>
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namespace swift {
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namespace threading_impl {
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namespace linux {
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typedef std::int32_t ulock_t;
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#define ULOCK_INITIALIZER 0
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#define ulock_fastpath(x) __builtin_expect((x), true)
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inline int ulock_get_tid(void) {
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static __thread int tid;
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if (tid == 0)
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tid = syscall(SYS_gettid);
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return tid;
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}
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inline int ulock_futex(ulock_t *lock, int op) {
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return syscall(SYS_futex, lock, op | FUTEX_PRIVATE_FLAG, 0, nullptr, nullptr,
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0);
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}
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inline void ulock_lock(ulock_t *lock) {
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const ulock_t tid = ulock_get_tid();
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do {
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ulock_t zero = 0;
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if (ulock_fastpath(__atomic_compare_exchange_n(
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lock, &zero, tid, true, __ATOMIC_ACQUIRE, __ATOMIC_RELAXED)))
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return;
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} while (ulock_futex(lock, FUTEX_LOCK_PI) != 0);
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}
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inline bool ulock_trylock(ulock_t *lock) {
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ulock_t zero = 0;
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if (ulock_fastpath(__atomic_compare_exchange_n(lock, &zero, ulock_get_tid(),
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true, __ATOMIC_ACQUIRE,
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__ATOMIC_RELAXED)))
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return true;
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return ulock_futex(lock, FUTEX_TRYLOCK_PI) == 0;
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}
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inline void ulock_unlock(ulock_t *lock) {
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const ulock_t tid = ulock_get_tid();
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do {
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ulock_t expected = tid;
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if (ulock_fastpath(__atomic_compare_exchange_n(
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lock, &expected, 0, true, __ATOMIC_RELEASE, __ATOMIC_RELAXED)))
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return;
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} while (ulock_futex(lock, FUTEX_UNLOCK_PI) != 0);
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}
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} // namespace linux
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} // namespace threading_impl
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} // namespace swift
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#endif // SWIFT_THREADING_IMPL_LINUX_ULOCK_H
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