1 //===-- Linux specific definitions for threads implementations. --*- C++ -*===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 9 #ifndef LLVM_LIBC_SRC_THREADS_LINUX_THREAD_UTILS_H 10 #define LLVM_LIBC_SRC_THREADS_LINUX_THREAD_UTILS_H 11 12 #include "thread_start_args.h" 13 14 #include <stdatomic.h> 15 #include <stdint.h> 16 17 namespace __llvm_libc { 18 19 // The futex data has to be exactly 4 bytes long. However, we use a uint type 20 // here as we do not want to use `_Atomic uint32_t` as the _Atomic keyword which 21 // is C only. The header stdatomic.h does not define an atomic type 22 // corresponding to `uint32_t` or to something which is exactly 4 bytes wide. 23 using FutexData = atomic_uint; 24 25 // We use a tri-state mutex because we want to avoid making syscalls 26 // as much as possible. In `mtx_unlock` a syscall to wake waiting threads is 27 // made only if the mutex status is `MutexStatus::Waiting`. 28 enum MutexStatus : uint32_t { MS_Free, MS_Locked, MS_Waiting }; 29 30 static_assert(sizeof(atomic_uint) == 4, 31 "Size of the `atomic_uint` type is not 4 bytes on your platform. " 32 "The implementation of the standard threads library for linux " 33 "requires that size of `atomic_uint` be 4 bytes."); 34 35 struct ThreadParams { 36 static constexpr uintptr_t DefaultStackSize = 1 << 16; // 64 KB 37 static constexpr uint32_t ClearTIDValue = 0xABCD1234; 38 }; 39 40 } // namespace __llvm_libc 41 42 #endif // LLVM_LIBC_SRC_THREADS_LINUX_THREAD_UTILS_H 43