Improve robustness of atomics
And fix increment in `CowData` not being conditional anymore after the recent changes. Co-authored-by: Hein-Pieter van Braam-Stewart <hp@tmm.cx>
This commit is contained in:
Pedro J. Estébanez
parent
001aaa7131
commit
55b5f98402
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@ -44,8 +44,9 @@ class CharString;
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template <class T, class V>
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class VMap;
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// CowData is relying on this to be true
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static_assert(sizeof(SafeNumeric<uint32_t>) == sizeof(uint32_t), "");
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#if !defined(NO_THREADS)
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SAFE_NUMERIC_TYPE_PUN_GUARANTEES(uint32_t)
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#endif
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template <class T>
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class CowData {
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@ -111,7 +112,7 @@ private:
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void _unref(void *p_data);
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void _ref(const CowData *p_from);
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void _ref(const CowData &p_from);
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void _copy_on_write();
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uint32_t _copy_on_write();
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public:
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void operator=(const CowData<T> &p_from) { _ref(p_from); }
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@ -217,20 +218,21 @@ void CowData<T>::_unref(void *p_data) {
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}
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template <class T>
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void CowData<T>::_copy_on_write() {
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uint32_t CowData<T>::_copy_on_write() {
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if (!_ptr)
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return;
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return 0;
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SafeNumeric<uint32_t> *refc = _get_refcount();
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if (unlikely(refc->get() > 1)) {
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uint32_t rc = refc->get();
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if (likely(rc > 1)) {
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/* in use by more than me */
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uint32_t current_size = *_get_size();
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uint32_t *mem_new = (uint32_t *)Memory::alloc_static(_get_alloc_size(current_size), true);
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reinterpret_cast<SafeNumeric<uint32_t> *>(mem_new - 2)->set(1); //refcount
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new (mem_new - 2, sizeof(uint32_t), "") SafeNumeric<uint32_t>(1); //refcount
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*(mem_new - 1) = current_size; //size
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T *_data = (T *)(mem_new);
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@ -247,7 +249,10 @@ void CowData<T>::_copy_on_write() {
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_unref(_ptr);
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_ptr = _data;
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rc = 1;
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}
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return rc;
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}
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template <class T>
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@ -268,7 +273,7 @@ Error CowData<T>::resize(int p_size) {
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}
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// possibly changing size, copy on write
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_copy_on_write();
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uint32_t rc = _copy_on_write();
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size_t current_alloc_size = _get_alloc_size(current_size);
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size_t alloc_size;
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@ -282,13 +287,15 @@ Error CowData<T>::resize(int p_size) {
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uint32_t *ptr = (uint32_t *)Memory::alloc_static(alloc_size, true);
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ERR_FAIL_COND_V(!ptr, ERR_OUT_OF_MEMORY);
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*(ptr - 1) = 0; //size, currently none
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reinterpret_cast<SafeNumeric<uint32_t> *>(ptr - 2)->set(1); //refcount
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new (ptr - 2, sizeof(uint32_t), "") SafeNumeric<uint32_t>(1); //refcount
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_ptr = (T *)ptr;
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} else {
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void *_ptrnew = (T *)Memory::realloc_static(_ptr, alloc_size, true);
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uint32_t *_ptrnew = (uint32_t *)Memory::realloc_static(_ptr, alloc_size, true);
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ERR_FAIL_COND_V(!_ptrnew, ERR_OUT_OF_MEMORY);
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new (_ptrnew - 2, sizeof(uint32_t), "") SafeNumeric<uint32_t>(rc); //refcount
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_ptr = (T *)(_ptrnew);
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}
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}
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@ -316,8 +323,9 @@ Error CowData<T>::resize(int p_size) {
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}
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if (alloc_size != current_alloc_size) {
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void *_ptrnew = (T *)Memory::realloc_static(_ptr, alloc_size, true);
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uint32_t *_ptrnew = (uint32_t *)Memory::realloc_static(_ptr, alloc_size, true);
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ERR_FAIL_COND_V(!_ptrnew, ERR_OUT_OF_MEMORY);
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new (_ptrnew - 2, sizeof(uint32_t), "") SafeNumeric<uint32_t>(rc); //refcount
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_ptr = (T *)(_ptrnew);
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}
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@ -363,7 +371,7 @@ void CowData<T>::_ref(const CowData &p_from) {
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if (!p_from._ptr)
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return; //nothing to do
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if (p_from._get_refcount()->increment() > 0) { // could reference
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if (p_from._get_refcount()->conditional_increment() > 0) { // could reference
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_ptr = p_from._ptr;
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}
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}
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@ -0,0 +1,45 @@
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/*************************************************************************/
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/* safe_refcount.cpp */
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/*************************************************************************/
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/* This file is part of: */
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/* GODOT ENGINE */
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/* https://godotengine.org */
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/*************************************************************************/
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/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur. */
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/* Copyright (c) 2014-2021 Godot Engine contributors (cf. AUTHORS.md). */
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/* */
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/* Permission is hereby granted, free of charge, to any person obtaining */
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/* a copy of this software and associated documentation files (the */
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/* "Software"), to deal in the Software without restriction, including */
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/* without limitation the rights to use, copy, modify, merge, publish, */
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/* distribute, sublicense, and/or sell copies of the Software, and to */
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/* permit persons to whom the Software is furnished to do so, subject to */
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/* the following conditions: */
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/* */
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/* The above copyright notice and this permission notice shall be */
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/* included in all copies or substantial portions of the Software. */
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/* */
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/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, */
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/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF */
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/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
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/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY */
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/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, */
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/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE */
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/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. */
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/*************************************************************************/
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#if defined(DEBUG_ENABLED) && !defined(NO_THREADS)
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#include "safe_refcount.h"
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#include "core/error_macros.h"
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// On C++14 we don't have std::atomic::is_always_lockfree, so this is the best we can do
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void check_lockless_atomics() {
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// Doing the check for the types we actually care about
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if (!std::atomic<uint32_t>{}.is_lock_free() || !std::atomic<uint64_t>{}.is_lock_free() || !std::atomic_bool{}.is_lock_free()) {
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WARN_PRINT("Your compiler doesn't seem to support lockless atomics. Performance will be degraded. Please consider upgrading to a different or newer compiler.");
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}
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}
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#endif
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@ -47,6 +47,16 @@
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// value and, as an important benefit, you can be sure the value is properly synchronized
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// even with threads that are already running.
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// This is used in very specific areas of the engine where it's critical that these guarantees are held
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#define SAFE_NUMERIC_TYPE_PUN_GUARANTEES(m_type) \
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static_assert(sizeof(SafeNumeric<m_type>) == sizeof(m_type), ""); \
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static_assert(alignof(SafeNumeric<m_type>) == alignof(m_type), ""); \
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static_assert(std::is_trivially_destructible<std::atomic<m_type> >::value, "");
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#if defined(DEBUG_ENABLED)
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void check_lockless_atomics();
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#endif
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template <class T>
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class SafeNumeric {
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std::atomic<T> value;
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@ -346,6 +346,10 @@ void Main::print_help(const char *p_binary) {
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*/
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Error Main::setup(const char *execpath, int argc, char *argv[], bool p_second_phase) {
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#if defined(DEBUG_ENABLED) && !defined(NO_THREADS)
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check_lockless_atomics();
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#endif
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RID_OwnerBase::init_rid();
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OS::get_singleton()->initialize_core();
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