Файл SDL_atomic.h

См. исходные тексты.

Классы
struct	SDL_atomic_t
	A type representing an atomic integer value. It is a struct so people don't accidentally use numeric operations on it. Подробнее...

SDL AtomicLock
The atomic locks are efficient spinlocks using CPU instructions, but are vulnerable to starvation and can spin forever if a thread holding a lock has been terminated. For this reason you should minimize the code executed inside an atomic lock and never do expensive things like API or system calls while holding them. The atomic locks are not safe to lock recursively. Porting Note: The spin lock functions and type are required and can not be emulated because they are used in the atomic emulation code.
typedef int	SDL_SpinLock
typedef void(*	SDL_KernelMemoryBarrierFunc) ()
DECLSPEC SDL_bool SDLCALL	SDL_AtomicTryLock (SDL_SpinLock *lock)
	Try to lock a spin lock by setting it to a non-zero value. Подробнее...
DECLSPEC void SDLCALL	SDL_AtomicLock (SDL_SpinLock *lock)
	Lock a spin lock by setting it to a non-zero value. Подробнее...
DECLSPEC void SDLCALL	SDL_AtomicUnlock (SDL_SpinLock *lock)
	Unlock a spin lock by setting it to 0. Always returns immediately. Подробнее...
void	_ReadWriteBarrier (void)
_inline void	SDL_CompilerBarrier (void)
DECLSPEC void SDLCALL	SDL_MemoryBarrierReleaseFunction (void)
DECLSPEC void SDLCALL	SDL_MemoryBarrierAcquireFunction (void)
DECLSPEC SDL_bool SDLCALL	SDL_AtomicCAS (SDL_atomic_t *a, int oldval, int newval)
	Set an atomic variable to a new value if it is currently an old value. Подробнее...
DECLSPEC int SDLCALL	SDL_AtomicSet (SDL_atomic_t *a, int v)
	Set an atomic variable to a value. Подробнее...
DECLSPEC int SDLCALL	SDL_AtomicGet (SDL_atomic_t *a)
	Get the value of an atomic variable. Подробнее...
DECLSPEC int SDLCALL	SDL_AtomicAdd (SDL_atomic_t *a, int v)
	Add to an atomic variable. Подробнее...
DECLSPEC SDL_bool SDLCALL	SDL_AtomicCASPtr (void **a, void *oldval, void *newval)
	Set a pointer to a new value if it is currently an old value. Подробнее...
DECLSPEC void *SDLCALL	SDL_AtomicSetPtr (void **a, void *v)
	Set a pointer to a value atomically. Подробнее...
DECLSPEC void *SDLCALL	SDL_AtomicGetPtr (void **a)
	Get the value of a pointer atomically. Подробнее...

Подробное описание

Atomic operations.

IMPORTANT: If you are not an expert in concurrent lockless programming, you should only be using the atomic lock and reference counting functions in this file. In all other cases you should be protecting your data structures with full mutexes.

The list of "safe" functions to use are: SDL_AtomicLock() SDL_AtomicUnlock() SDL_AtomicIncRef() SDL_AtomicDecRef()

Seriously, here be dragons! ^^^^^^^^^^^^^^^^^^^^^^^^^^^

You can find out a little more about lockless programming and the subtle issues that can arise here: http://msdn.microsoft.com/en-us/library/ee418650%28v=vs.85%29.aspx

There's also lots of good information here: http://www.1024cores.net/home/lock-free-algorithms http://preshing.com/

These operations may or may not actually be implemented using processor specific atomic operations. When possible they are implemented as true processor specific atomic operations. When that is not possible the are implemented using locks that do use the available atomic operations.

All of the atomic operations that modify memory are full memory barriers.

См. определение в файле SDL_atomic.h

Типы

SDL_SpinLock

typedef int SDL_SpinLock

См. определение в файле SDL_atomic.h строка 89

SDL_KernelMemoryBarrierFunc

typedef void(* SDL_KernelMemoryBarrierFunc) ()

См. определение в файле SDL_atomic.h строка 172

Функции

SDL_AtomicTryLock()

DECLSPEC SDL_bool SDLCALL SDL_AtomicTryLock

(

SDL_SpinLock *

lock

)

Try to lock a spin lock by setting it to a non-zero value.

Аргументы

lock	Points to the lock.

Возвращает

SDL_TRUE if the lock succeeded, SDL_FALSE if the lock is already held.

SDL_AtomicLock()

DECLSPEC void SDLCALL SDL_AtomicLock

(

SDL_SpinLock *

lock

)

Lock a spin lock by setting it to a non-zero value.

Аргументы

lock	Points to the lock.

SDL_AtomicUnlock()

DECLSPEC void SDLCALL SDL_AtomicUnlock

(

SDL_SpinLock *

lock

)

Unlock a spin lock by setting it to 0. Always returns immediately.

Аргументы

lock	Points to the lock.

_ReadWriteBarrier()

void _ReadWriteBarrier

(

void

)

The compiler barrier prevents the compiler from reordering reads and writes to globally visible variables across the call.

SDL_CompilerBarrier()

_inline void SDL_CompilerBarrier

(

void

)

SDL_MemoryBarrierReleaseFunction()

DECLSPEC void SDLCALL SDL_MemoryBarrierReleaseFunction

(

void

)

Memory barriers are designed to prevent reads and writes from being reordered by the compiler and being seen out of order on multi-core CPUs.

A typical pattern would be for thread A to write some data and a flag, and for thread B to read the flag and get the data. In this case you would insert a release barrier between writing the data and the flag, guaranteeing that the data write completes no later than the flag is written, and you would insert an acquire barrier between reading the flag and reading the data, to ensure that all the reads associated with the flag have completed.

In this pattern you should always see a release barrier paired with an acquire barrier and you should gate the data reads/writes with a single flag variable.

For more information on these semantics, take a look at the blog post: http://preshing.com/20120913/acquire-and-release-semantics

SDL_MemoryBarrierAcquireFunction()

DECLSPEC void SDLCALL SDL_MemoryBarrierAcquireFunction

(

void

)

SDL_AtomicCAS()

DECLSPEC SDL_bool SDLCALL SDL_AtomicCAS	(	SDL_atomic_t *	a,
		int	oldval,
		int	newval
	)

Set an atomic variable to a new value if it is currently an old value.

Возвращает

SDL_TRUE if the atomic variable was set, SDL_FALSE otherwise.

Заметки

If you don't know what this function is for, you shouldn't use it!

SDL_AtomicSet()

DECLSPEC int SDLCALL SDL_AtomicSet	(	SDL_atomic_t *	a,
		int	v
	)

Set an atomic variable to a value.

Возвращает

The previous value of the atomic variable.

SDL_AtomicGet()

DECLSPEC int SDLCALL SDL_AtomicGet

(

SDL_atomic_t *

a

)

Get the value of an atomic variable.

SDL_AtomicAdd()

DECLSPEC int SDLCALL SDL_AtomicAdd	(	SDL_atomic_t *	a,
		int	v
	)

Add to an atomic variable.

Возвращает

The previous value of the atomic variable.

Заметки

This same style can be used for any number operation

SDL_AtomicCASPtr()

DECLSPEC SDL_bool SDLCALL SDL_AtomicCASPtr	(	void **	a,
		void *	oldval,
		void *	newval
	)

Set a pointer to a new value if it is currently an old value.

Возвращает

SDL_TRUE if the pointer was set, SDL_FALSE otherwise.

Заметки

If you don't know what this function is for, you shouldn't use it!

SDL_AtomicSetPtr()

DECLSPEC void* SDLCALL SDL_AtomicSetPtr	(	void **	a,
		void *	v
	)

Set a pointer to a value atomically.

Возвращает

The previous value of the pointer.

SDL_AtomicGetPtr()

DECLSPEC void* SDLCALL SDL_AtomicGetPtr

(

void **

a

)

Get the value of a pointer atomically.