initial commit, 4.5 stable

core/os/spin_lock.h

@@ -0,0 +1,128 @@
+/**************************************************************************/
+/*  spin_lock.h                                                           */
+/**************************************************************************/
+/*                         This file is part of:                          */
+/*                             GODOT ENGINE                               */
+/*                        https://godotengine.org                         */
+/**************************************************************************/
+/* Copyright (c) 2014-present Godot Engine contributors (see AUTHORS.md). */
+/* Copyright (c) 2007-2014 Juan Linietsky, Ariel Manzur.                  */
+/*                                                                        */
+/* Permission is hereby granted, free of charge, to any person obtaining  */
+/* a copy of this software and associated documentation files (the        */
+/* "Software"), to deal in the Software without restriction, including    */
+/* without limitation the rights to use, copy, modify, merge, publish,    */
+/* distribute, sublicense, and/or sell copies of the Software, and to     */
+/* permit persons to whom the Software is furnished to do so, subject to  */
+/* the following conditions:                                              */
+/*                                                                        */
+/* The above copyright notice and this permission notice shall be         */
+/* included in all copies or substantial portions of the Software.        */
+/*                                                                        */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,        */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF     */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. */
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY   */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,   */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE      */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                 */
+/**************************************************************************/
+
+#pragma once
+
+#include "core/os/thread.h"
+#include "core/typedefs.h"
+
+#ifdef THREADS_ENABLED
+
+// Note the implementations below avoid false sharing by ensuring their
+// sizes match the assumed cache line. We can't use align attributes
+// because these objects may end up unaligned in semi-tightly packed arrays.
+
+#ifdef _MSC_VER
+#include <intrin.h>
+#endif
+
+#if defined(__APPLE__)
+
+#include <os/lock.h>
+
+class SpinLock {
+	union {
+		mutable os_unfair_lock _lock = OS_UNFAIR_LOCK_INIT;
+		char aligner[Thread::CACHE_LINE_BYTES];
+	};
+
+public:
+	_ALWAYS_INLINE_ void lock() const {
+		os_unfair_lock_lock(&_lock);
+	}
+
+	_ALWAYS_INLINE_ void unlock() const {
+		os_unfair_lock_unlock(&_lock);
+	}
+};
+
+#else // __APPLE__
+
+#include <atomic>
+
+_ALWAYS_INLINE_ static void _cpu_pause() {
+#if defined(_MSC_VER)
+// ----- MSVC.
+#if defined(_M_ARM) || defined(_M_ARM64) // ARM.
+	__yield();
+#elif defined(_M_IX86) || defined(_M_X64) // x86.
+	_mm_pause();
+#endif
+#elif defined(__GNUC__) || defined(__clang__)
+// ----- GCC/Clang.
+#if defined(__i386__) || defined(__x86_64__) // x86.
+	__builtin_ia32_pause();
+#elif defined(__arm__) || defined(__aarch64__) // ARM.
+	asm volatile("yield");
+#elif defined(__powerpc__) // PowerPC.
+	asm volatile("or 27,27,27");
+#elif defined(__riscv) // RISC-V.
+	asm volatile(".insn i 0x0F, 0, x0, x0, 0x010");
+#endif
+#endif
+}
+
+static_assert(std::atomic_bool::is_always_lock_free);
+
+class SpinLock {
+	union {
+		mutable std::atomic<bool> locked = ATOMIC_VAR_INIT(false);
+		char aligner[Thread::CACHE_LINE_BYTES];
+	};
+
+public:
+	_ALWAYS_INLINE_ void lock() const {
+		while (true) {
+			bool expected = false;
+			if (locked.compare_exchange_weak(expected, true, std::memory_order_acquire, std::memory_order_relaxed)) {
+				break;
+			}
+			do {
+				_cpu_pause();
+			} while (locked.load(std::memory_order_relaxed));
+		}
+	}
+
+	_ALWAYS_INLINE_ void unlock() const {
+		locked.store(false, std::memory_order_release);
+	}
+};
+
+#endif // __APPLE__
+
+#else // THREADS_ENABLED
+
+class SpinLock {
+public:
+	void lock() const {}
+	void unlock() const {}
+};
+
+#endif // THREADS_ENABLED