godot/core/safe_refcount.h

/*************************************************************************/
/*  safe_refcount.h                                                      */
/*************************************************************************/
/*                       This file is part of:                           */
/*                           GODOT ENGINE                                */
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/* Copyright (c) 2007-2018 Juan Linietsky, Ariel Manzur.                 */
/* Copyright (c) 2014-2018 Godot Engine contributors (cf. AUTHORS.md)    */
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/*************************************************************************/
#ifndef SAFE_REFCOUNT_H
#define SAFE_REFCOUNT_H

#include "os/mutex.h"
/* x86/x86_64 GCC */

#include "platform_config.h"

#ifdef NO_THREADS

struct SafeRefCount {

	int count;

public:
	// destroy() is called when weak_count_ drops to zero.

	bool ref() { //true on success

		if (count == 0)
			return false;
		count++;

		return true;
	}

	int refval() { //true on success

		if (count == 0)
			return 0;
		count++;
		return count;
	}

	bool unref() { // true if must be disposed of

		if (count > 0)
			count--;

		return count == 0;
	}

	long get() const { // nothrow

		return static_cast<int const volatile &>(count);
	}

	void init(int p_value = 1) {

		count = p_value;
	};
};

#else

#if defined(PLATFORM_REFCOUNT)

#include "platform_refcount.h"

#elif defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))

#define REFCOUNT_T volatile int
#define REFCOUNT_GET_T int const volatile &

static inline int atomic_conditional_increment(volatile int *pw) {
	// int rv = *pw;
	// if( rv != 0 ) ++*pw;
	// return rv;

	int rv, tmp;

	__asm__(
			"movl %0, %%eax\n\t"
			"0:\n\t"
			"test %%eax, %%eax\n\t"
			"je 1f\n\t"
			"movl %%eax, %2\n\t"
			"incl %2\n\t"
			"lock\n\t"
			"cmpxchgl %2, %0\n\t"
			"jne 0b\n\t"
			"1:"
			: "=m"(*pw), "=&a"(rv), "=&r"(tmp)
			: // outputs (%0, %1, %2)
			"m"(*pw)
			: // input (%3)
			"cc" // clobbers
	);

	return rv;
}

static inline int atomic_decrement(volatile int *pw) {

	// return --(*pw);

	unsigned char rv;

	__asm__(
			"lock\n\t"
			"decl %0\n\t"
			"setne %1"
			: "=m"(*pw), "=qm"(rv)
			: "m"(*pw)
			: "memory");
	return static_cast<int>(rv);
}

	/* PowerPC32/64 GCC */

#elif (defined(__GNUC__)) && (defined(__powerpc__) || defined(__ppc__))

#define REFCOUNT_T int
#define REFCOUNT_GET_T int const volatile &

inline int atomic_conditional_increment(int *pw) {
	// if( *pw != 0 ) ++*pw;
	// return *pw;

	int rv;

	__asm__(
			"0:\n\t"
			"lwarx %1, 0, %2\n\t"
			"cmpwi %1, 0\n\t"
			"beq 1f\n\t"
			"addi %1, %1, 1\n\t"
			"1:\n\t"
			"stwcx. %1, 0, %2\n\t"
			"bne- 0b"
			:

			"=m"(*pw), "=&b"(rv)
			: "r"(pw), "m"(*pw)
			: "cc");

	return rv;
}

inline int atomic_decrement(int *pw) {
	// return --*pw;

	int rv;

	__asm__ __volatile__(
			"sync\n\t"
			"0:\n\t"
			"lwarx %1, 0, %2\n\t"
			"addi %1, %1, -1\n\t"
			"stwcx. %1, 0, %2\n\t"
			"bne- 0b\n\t"
			"isync"
			:

			"=m"(*pw), "=&b"(rv)
			: "r"(pw), "m"(*pw)
			: "memory", "cc");

	return rv;
}

	/* CW ARM */

#elif defined(__GNUC__) && (defined(__arm__))

#define REFCOUNT_T int
#define REFCOUNT_GET_T int const volatile &

inline int atomic_conditional_increment(volatile int *v) {
	int t;
	int tmp;

	__asm__ __volatile__(
			"1:  ldrex   %0, [%2]        \n"
			"    cmp     %0, #0      \n"
			"    beq     2f          \n"
			"    add     %0, %0, #1      \n"
			"2: \n"
			"    strex   %1, %0, [%2]    \n"
			"    cmp     %1, #0          \n"
			"    bne     1b              \n"

			: "=&r"(t), "=&r"(tmp)
			: "r"(v)
			: "cc", "memory");

	return t;
}

inline int atomic_decrement(volatile int *v) {
	int t;
	int tmp;

	__asm__ __volatile__(
			"1:  ldrex   %0, [%2]        \n"
			"    add     %0, %0, #-1      \n"
			"    strex   %1, %0, [%2]    \n"
			"    cmp     %1, #0          \n"
			"    bne     1b              \n"

			: "=&r"(t), "=&r"(tmp)
			: "r"(v)
			: "cc", "memory");

	return t;
}

	/* CW PPC */

#elif (defined(__MWERKS__)) && defined(__POWERPC__)

inline long atomic_conditional_increment(register long *pw) {
	register int a;

	asm {
	loop:

	lwarx   a, 0, pw
	cmpwi   a, 0
	beq     store

	addi    a, a, 1

	store:

	stwcx.  a, 0, pw
	bne-    loop
	}

	return a;
}

inline long atomic_decrement(register long *pw) {
	register int a;

	asm {

	sync

	loop:

	lwarx   a, 0, pw
	addi    a, a, -1
	stwcx.  a, 0, pw
	bne-    loop

	isync
	}

	return a;
}

	/* Any Windows (MSVC) */

#elif defined(_MSC_VER)

// made functions to not pollute namespace..

#define REFCOUNT_T long
#define REFCOUNT_GET_T long const volatile &

long atomic_conditional_increment(register long *pw);
long atomic_decrement(register long *pw);

#if 0
#elif defined(__GNUC__) && defined(ARMV6_ENABLED)

#endif

#else

#error This platform cannot use safe refcount, compile with NO_THREADS or implement it.

#endif

struct SafeRefCount {

	REFCOUNT_T count;

public:
	// destroy() is called when weak_count_ drops to zero.

	bool ref() { //true on success

		return atomic_conditional_increment(&count) != 0;
	}

	int refval() { //true on success

		return atomic_conditional_increment(&count);
	}

	bool unref() { // true if must be disposed of

		if (atomic_decrement(&count) == 0) {
			return true;
		}

		return false;
	}

	long get() const { // nothrow

		return static_cast<REFCOUNT_GET_T>(count);
	}

	void init(int p_value = 1) {

		count = p_value;
	};
};

#endif // no thread safe

#endif