godot/core/safe_refcount.cpp

/*************************************************************************/
/*  safe_refcount.cpp                                                    */
/*************************************************************************/
/*                       This file is part of:                           */
/*                           GODOT ENGINE                                */
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/* Copyright (c) 2007-2020 Juan Linietsky, Ariel Manzur.                 */
/* Copyright (c) 2014-2020 Godot Engine contributors (cf. AUTHORS.md).   */
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#include "safe_refcount.h"

// Atomic functions, these are used for multithread safe reference counters!

#ifdef NO_THREADS

/* Bogus implementation unaware of multiprocessing */

template <class T>
static _ALWAYS_INLINE_ T _atomic_conditional_increment_impl(register T *pw) {

	if (*pw == 0)
		return 0;

	(*pw)++;

	return *pw;
}

template <class T>
static _ALWAYS_INLINE_ T _atomic_decrement_impl(register T *pw) {

	(*pw)--;

	return *pw;
}

template <class T>
static _ALWAYS_INLINE_ T _atomic_increment_impl(register T *pw) {

	(*pw)++;

	return *pw;
}

template <class T>
static _ALWAYS_INLINE_ T _atomic_sub_impl(register T *pw, register T val) {

	(*pw) -= val;

	return *pw;
}

template <class T>
static _ALWAYS_INLINE_ T _atomic_add_impl(register T *pw, register T val) {

	(*pw) += val;

	return *pw;
}

template <class T>
static _ALWAYS_INLINE_ T _atomic_exchange_if_greater_impl(register T *pw, register T val) {

	if (val > *pw)
		*pw = val;

	return *pw;
}

#elif defined(__GNUC__)

/* Implementation for GCC & Clang */

// GCC guarantees atomic intrinsics for sizes of 1, 2, 4 and 8 bytes.
// Clang states it supports GCC atomic builtins.

template <class T>
static _ALWAYS_INLINE_ T _atomic_conditional_increment_impl(register T *pw) {

	while (true) {
		T tmp = static_cast<T const volatile &>(*pw);
		if (tmp == 0)
			return 0; // if zero, can't add to it anymore
		if (__sync_val_compare_and_swap(pw, tmp, tmp + 1) == tmp)
			return tmp + 1;
	}
}

template <class T>
static _ALWAYS_INLINE_ T _atomic_decrement_impl(register T *pw) {

	return __sync_sub_and_fetch(pw, 1);
}

template <class T>
static _ALWAYS_INLINE_ T _atomic_increment_impl(register T *pw) {

	return __sync_add_and_fetch(pw, 1);
}

template <class T>
static _ALWAYS_INLINE_ T _atomic_sub_impl(register T *pw, register T val) {

	return __sync_sub_and_fetch(pw, val);
}

template <class T>
static _ALWAYS_INLINE_ T _atomic_add_impl(register T *pw, register T val) {

	return __sync_add_and_fetch(pw, val);
}

template <class T>
static _ALWAYS_INLINE_ T _atomic_exchange_if_greater_impl(register T *pw, register T val) {

	while (true) {
		T tmp = static_cast<T const volatile &>(*pw);
		if (tmp >= val)
			return tmp; // already greater, or equal
		if (__sync_val_compare_and_swap(pw, tmp, val) == tmp)
			return val;
	}
}

#elif defined(_MSC_VER)

/* Implementation for MSVC-Windows */

// don't pollute my namespace!
#include <windows.h>

#define ATOMIC_CONDITIONAL_INCREMENT_BODY(m_pw, m_win_type, m_win_cmpxchg, m_cpp_type) \
	/* try to increment until it actually works */                                     \
	/* taken from boost */                                                             \
	while (true) {                                                                     \
		m_cpp_type tmp = static_cast<m_cpp_type const volatile &>(*(m_pw));            \
		if (tmp == 0)                                                                  \
			return 0; /* if zero, can't add to it anymore */                           \
		if (m_win_cmpxchg((m_win_type volatile *)(m_pw), tmp + 1, tmp) == tmp)         \
			return tmp + 1;                                                            \
	}

#define ATOMIC_EXCHANGE_IF_GREATER_BODY(m_pw, m_val, m_win_type, m_win_cmpxchg, m_cpp_type) \
	while (true) {                                                                          \
		m_cpp_type tmp = static_cast<m_cpp_type const volatile &>(*(m_pw));                 \
		if (tmp >= m_val)                                                                   \
			return tmp; /* already greater, or equal */                                     \
		if (m_win_cmpxchg((m_win_type volatile *)(m_pw), m_val, tmp) == tmp)                \
			return m_val;                                                                   \
	}

static _ALWAYS_INLINE_ uint32_t _atomic_conditional_increment_impl(register uint32_t *pw) {

	ATOMIC_CONDITIONAL_INCREMENT_BODY(pw, LONG, InterlockedCompareExchange, uint32_t)
}

static _ALWAYS_INLINE_ uint32_t _atomic_decrement_impl(register uint32_t *pw) {

	return InterlockedDecrement((LONG volatile *)pw);
}

static _ALWAYS_INLINE_ uint32_t _atomic_increment_impl(register uint32_t *pw) {

	return InterlockedIncrement((LONG volatile *)pw);
}

static _ALWAYS_INLINE_ uint32_t _atomic_sub_impl(register uint32_t *pw, register uint32_t val) {

	return InterlockedExchangeAdd((LONG volatile *)pw, -(int32_t)val) - val;
}

static _ALWAYS_INLINE_ uint32_t _atomic_add_impl(register uint32_t *pw, register uint32_t val) {

	return InterlockedAdd((LONG volatile *)pw, val);
}

static _ALWAYS_INLINE_ uint32_t _atomic_exchange_if_greater_impl(register uint32_t *pw, register uint32_t val) {

	ATOMIC_EXCHANGE_IF_GREATER_BODY(pw, val, LONG, InterlockedCompareExchange, uint32_t)
}

static _ALWAYS_INLINE_ uint64_t _atomic_conditional_increment_impl(register uint64_t *pw) {

	ATOMIC_CONDITIONAL_INCREMENT_BODY(pw, LONGLONG, InterlockedCompareExchange64, uint64_t)
}

static _ALWAYS_INLINE_ uint64_t _atomic_decrement_impl(register uint64_t *pw) {

	return InterlockedDecrement64((LONGLONG volatile *)pw);
}

static _ALWAYS_INLINE_ uint64_t _atomic_increment_impl(register uint64_t *pw) {

	return InterlockedIncrement64((LONGLONG volatile *)pw);
}

static _ALWAYS_INLINE_ uint64_t _atomic_sub_impl(register uint64_t *pw, register uint64_t val) {

	return InterlockedExchangeAdd64((LONGLONG volatile *)pw, -(int64_t)val) - val;
}

static _ALWAYS_INLINE_ uint64_t _atomic_add_impl(register uint64_t *pw, register uint64_t val) {

	return InterlockedAdd64((LONGLONG volatile *)pw, val);
}

static _ALWAYS_INLINE_ uint64_t _atomic_exchange_if_greater_impl(register uint64_t *pw, register uint64_t val) {

	ATOMIC_EXCHANGE_IF_GREATER_BODY(pw, val, LONGLONG, InterlockedCompareExchange64, uint64_t)
}

#else

//no threads supported?
#error Must provide atomic functions for this platform or compiler!

#endif

// The actual advertised functions; they'll call the right implementation

uint32_t atomic_conditional_increment(register uint32_t *counter) {
	return _atomic_conditional_increment_impl(counter);
}

uint32_t atomic_decrement(register uint32_t *pw) {
	return _atomic_decrement_impl(pw);
}

uint32_t atomic_increment(register uint32_t *pw) {
	return _atomic_increment_impl(pw);
}

uint32_t atomic_sub(register uint32_t *pw, register uint32_t val) {
	return _atomic_sub_impl(pw, val);
}

uint32_t atomic_add(register uint32_t *pw, register uint32_t val) {
	return _atomic_add_impl(pw, val);
}

uint32_t atomic_exchange_if_greater(register uint32_t *pw, register uint32_t val) {
	return _atomic_exchange_if_greater_impl(pw, val);
}

uint64_t atomic_conditional_increment(register uint64_t *counter) {
	return _atomic_conditional_increment_impl(counter);
}

uint64_t atomic_decrement(register uint64_t *pw) {
	return _atomic_decrement_impl(pw);
}

uint64_t atomic_increment(register uint64_t *pw) {
	return _atomic_increment_impl(pw);
}

uint64_t atomic_sub(register uint64_t *pw, register uint64_t val) {
	return _atomic_sub_impl(pw, val);
}

uint64_t atomic_add(register uint64_t *pw, register uint64_t val) {
	return _atomic_add_impl(pw, val);
}

uint64_t atomic_exchange_if_greater(register uint64_t *pw, register uint64_t val) {
	return _atomic_exchange_if_greater_impl(pw, val);
}