Updated the atomic API for better use cases

This commit is contained in:
Sam Lantinga 2011-01-15 12:41:59 -08:00
parent 4084438113
commit 1bc8fe69ce
16 changed files with 488 additions and 2758 deletions

View file

@ -18,24 +18,34 @@
Sam Lantinga
slouken@libsdl.org
Contributed by Bob Pendleton, bob@pendleton.com
*/
/**
* \file SDL_atomic.h
*
* Atomic operations.
*
* 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.
*
* At the very minimum spin locks must be implemented. Without spin
* locks it is not possible (AFAICT) to emulate the rest of the atomic
* operations.
* \file SDL_atomic.h
*
* 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!
*
* 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.
*/
#ifndef _SDL_atomic_h_
@ -53,154 +63,138 @@ extern "C" {
/* *INDENT-ON* */
#endif
/* Function prototypes */
/**
* \name SDL AtomicLock
*
* The spin lock functions and type are required and can not be
* emulated because they are used in the emulation code.
* \name 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 volatile Uint32 SDL_SpinLock;
typedef int SDL_SpinLock;
/**
* \brief Lock a spin lock by setting it to a none zero value.
*
* \param lock Points to the lock.
* \brief Try to lock a spin lock by setting it to a non-zero value.
*
* \param lock Points to the lock.
*
* \return SDL_TRUE if the lock succeeded, SDL_FALSE if the lock is already held.
*/
extern DECLSPEC SDL_bool SDLCALL SDL_AtomicTryLock(SDL_SpinLock *lock);
/**
* \brief Lock a spin lock by setting it to a non-zero value.
*
* \param lock Points to the lock.
*/
extern DECLSPEC void SDLCALL SDL_AtomicLock(SDL_SpinLock *lock);
/**
* \brief Unlock a spin lock by setting it to 0. Always returns immediately
* \brief Unlock a spin lock by setting it to 0. Always returns immediately
*
* \param lock Points to the lock.
* \param lock Points to the lock.
*/
extern DECLSPEC void SDLCALL SDL_AtomicUnlock(SDL_SpinLock *lock);
/*@}*//*SDL AtomicLock*/
/**
* \name 32 bit atomic operations
*/
/*@{*/
/* Platform specific optimized versions of the atomic functions */
/* None yet... */
/**
* \brief Check to see if \c *ptr == 0 and set it to 1.
*
* \return SDL_True if the value pointed to by \c ptr was zero and
* SDL_False if it was not zero
*
* \param ptr Points to the value to be tested and set.
* \brief A type representing an atomic integer value. It is a struct
* so people don't accidentally use numeric operations on it.
*/
extern DECLSPEC SDL_bool SDLCALL SDL_AtomicTestThenSet32(volatile Uint32 * ptr);
#ifndef SDL_atomic_t_defined
typedef struct { int value; } SDL_atomic_t;
#endif
/**
* \brief Set the value pointed to by \c ptr to be zero.
*
* \param ptr Address of the value to be set to zero
* \brief Set an atomic variable to a value.
*
* \return The previous value of the atomic variable.
*/
extern DECLSPEC void SDLCALL SDL_AtomicClear32(volatile Uint32 * ptr);
#ifndef SDL_AtomicSet
extern DECLSPEC int SDLCALL SDL_AtomicSet(SDL_atomic_t *a, int value);
#endif
/**
* \brief Fetch the current value of \c *ptr and then increment that
* value in place.
*
* \return The value before it was incremented.
*
* \param ptr Address of the value to fetch and increment
* \brief Get the value of an atomic variable
*/
extern DECLSPEC Uint32 SDLCALL SDL_AtomicFetchThenIncrement32(volatile Uint32 * ptr);
#ifndef SDL_AtomicGet
extern DECLSPEC int SDLCALL SDL_AtomicGet(SDL_atomic_t *a);
#endif
/**
* \brief Fetch \c *ptr and then decrement the value in place.
*
* \return The value before it was decremented.
*
* \param ptr Address of the value to fetch and decrement
* \brief Add to an atomic variable.
*
* \return The previous value of the atomic variable.
*/
extern DECLSPEC Uint32 SDLCALL SDL_AtomicFetchThenDecrement32(volatile Uint32 * ptr);
#ifndef SDL_AtomicAdd
extern DECLSPEC int SDLCALL SDL_AtomicAdd(SDL_atomic_t *a, int value);
#endif
/**
* \brief Fetch the current value at \c ptr and then add \c value to \c *ptr.
*
* \return \c *ptr before the addition took place.
*
* \param ptr The address of data we are changing.
* \param value The value to add to \c *ptr.
* \brief Increment an atomic variable used as a reference count.
*/
extern DECLSPEC Uint32 SDLCALL SDL_AtomicFetchThenAdd32(volatile Uint32 * ptr, Uint32 value);
#ifndef SDL_AtomicIncRef
extern DECLSPEC void SDLCALL SDL_AtomicIncRef(SDL_atomic_t *a);
#endif
/**
* \brief Fetch \c *ptr and then subtract \c value from it.
*
* \return \c *ptr before the subtraction took place.
*
* \param ptr The address of the data being changed.
* \param value The value to subtract from \c *ptr.
* \brief Decrement an atomic variable used as a reference count.
*
* \return SDL_TRUE if the variable has reached zero after decrementing,
* SDL_FALSE otherwise
*/
extern DECLSPEC Uint32 SDLCALL SDL_AtomicFetchThenSubtract32(volatile Uint32 * ptr, Uint32 value);
#ifndef SDL_AtomicDecRef
extern DECLSPEC SDL_bool SDLCALL SDL_AtomicDecRef(SDL_atomic_t *a);
#endif
/**
* \brief Add one to the data pointed to by \c ptr and return that value.
*
* \return The incremented value.
*
* \param ptr The address of the data to increment.
*/
extern DECLSPEC Uint32 SDLCALL SDL_AtomicIncrementThenFetch32(volatile Uint32 * ptr);
* \brief Set an atomic variable to a new value if it is currently an old value.
*
* \return The previous value of the atomic variable
*
* \note If you don't know what this function is for, you shouldn't use it!
*/
#ifndef SDL_AtomicCAS
extern DECLSPEC int SDLCALL SDL_AtomicCAS(SDL_atomic_t *a, int oldval, int newval);
#endif
/**
* \brief Subtract one from data pointed to by \c ptr and return the new value.
*
* \return The decremented value.
*
* \param ptr The address of the data to decrement.
* \brief Set a pointer to a value atomically.
*/
extern DECLSPEC Uint32 SDLCALL SDL_AtomicDecrementThenFetch32(volatile Uint32 * ptr);
#ifndef SDL_AtomicSetPtr
extern DECLSPEC void SDLCALL SDL_AtomicSetPtr(void** a, void* value);
#endif
/**
* \brief Add \c value to the data pointed to by \c ptr and return result.
*
* \return The sum of \c *ptr and \c value.
*
* \param ptr The address of the data to be modified.
* \param value The value to be added.
* \brief Get the value of a pointer atomically.
*/
extern DECLSPEC Uint32 SDLCALL SDL_AtomicAddThenFetch32(volatile Uint32 * ptr, Uint32 value);
#ifndef SDL_AtomicGetPtr
extern DECLSPEC void* SDLCALL SDL_AtomicGetPtr(void** a);
#endif
/**
* \brief Subtract \c value from the data pointed to by \c ptr and return the result.
*
* \return The difference between \c *ptr and \c value.
*
* \param ptr The address of the data to be modified.
* \param value The value to be subtracted.
*/
extern DECLSPEC Uint32 SDLCALL SDL_AtomicSubtractThenFetch32(volatile Uint32 * ptr, Uint32 value);
/*@}*//*32 bit atomic operations*/
/**
* \name 64 bit atomic operations
*/
/*@{*/
#ifdef SDL_HAS_64BIT_TYPE
extern DECLSPEC SDL_bool SDLCALL SDL_AtomicTestThenSet64(volatile Uint64 * ptr);
extern DECLSPEC void SDLCALL SDL_AtomicClear64(volatile Uint64 * ptr);
extern DECLSPEC Uint64 SDLCALL SDL_AtomicFetchThenIncrement64(volatile Uint64 * ptr);
extern DECLSPEC Uint64 SDLCALL SDL_AtomicFetchThenDecrement64(volatile Uint64 * ptr);
extern DECLSPEC Uint64 SDLCALL SDL_AtomicFetchThenAdd64(volatile Uint64 * ptr, Uint64 value);
extern DECLSPEC Uint64 SDLCALL SDL_AtomicFetchThenSubtract64(volatile Uint64 * ptr, Uint64 value);
extern DECLSPEC Uint64 SDLCALL SDL_AtomicIncrementThenFetch64(volatile Uint64 * ptr);
extern DECLSPEC Uint64 SDLCALL SDL_AtomicDecrementThenFetch64(volatile Uint64 * ptr);
extern DECLSPEC Uint64 SDLCALL SDL_AtomicAddThenFetch64(volatile Uint64 * ptr, Uint64 value);
extern DECLSPEC Uint64 SDLCALL SDL_AtomicSubtractThenFetch64(volatile Uint64 * ptr, Uint64 value);
#endif /* SDL_HAS_64BIT_TYPE */
/*@}*//*64 bit atomic operations*/
* \brief Set a pointer to a new value if it is currently an old value.
*
* \return The previous value of the pointer
*
* \note If you don't know what this function is for, you shouldn't use it!
*/
#ifndef SDL_AtomicCASPtr
extern DECLSPEC void* SDLCALL SDL_AtomicCASPtr(void **a, void *oldval, void *newval);
#endif
/* Ends C function definitions when using C++ */
#ifdef __cplusplus