[mirror_edk2.git] / MdePkg / Library / BaseLib / Synchronization.c

/** @file\r
  Implementation of synchronization functions.\r
\r
  Copyright (c) 2006, Intel Corporation<BR>\r
  All rights reserved. This program and the accompanying materials\r
  are licensed and made available under the terms and conditions of the BSD License\r
  which accompanies this distribution.  The full text of the license may be found at\r
  http://opensource.org/licenses/bsd-license.php\r
\r
  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,\r
  WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.\r
\r
  Module Name:  Synchronization.c\r
\r
**/\r
\r
#include "BaseLibInternals.h"\r
\r
#define SPIN_LOCK_RELEASED          ((UINTN) 1)\r
#define SPIN_LOCK_ACQUIRED          ((UINTN) 2)\r
\r
/**\r
  Retrieves the architecture specific spin lock alignment requirements for\r
  optimal spin lock performance.\r
\r
  This function retrieves the spin lock alignment requirements for optimal\r
  performance on a given CPU architecture. The spin lock alignment must be a\r
  power of two and is returned by this function. If there are no alignment\r
  requirements, then 1 must be returned. The spin lock synchronization\r
  functions must function correctly if the spin lock size and alignment values\r
  returned by this function are not used at all. These values are hints to the\r
  consumers of the spin lock synchronization functions to obtain optimal spin\r
  lock performance.\r
\r
  @return The architecture specific spin lock alignment.\r
\r
**/\r
UINTN\r
EFIAPI\r
GetSpinLockProperties (\r
  VOID\r
  )\r
{\r
  // @bug May use a PCD entry to determine this alignment.\r
  return 32;\r
}\r
\r
/**\r
  Initializes a spin lock to the released state and returns the spin lock.\r
\r
  This function initializes the spin lock specified by SpinLock to the released\r
  state, and returns SpinLock. Optimal performance can be achieved by calling\r
  GetSpinLockProperties() to determine the size and alignment requirements for\r
  SpinLock.\r
\r
  If SpinLock is NULL, then ASSERT().\r
\r
  @param  SpinLock  A pointer to the spin lock to initialize to the released\r
                    state.\r
\r
  @return SpinLock\r
\r
**/\r
SPIN_LOCK *\r
EFIAPI\r
InitializeSpinLock (\r
  OUT     SPIN_LOCK                 *SpinLock\r
  )\r
{\r
  ASSERT (SpinLock != NULL);\r
  *SpinLock = SPIN_LOCK_RELEASED;\r
  return SpinLock;\r
}\r
\r
/**\r
  Waits until a spin lock can be placed in the acquired state.\r
\r
  This function checks the state of the spin lock specified by SpinLock. If\r
  SpinLock is in the released state, then this function places SpinLock in the\r
  acquired state and returns SpinLock. Otherwise, this function waits\r
  indefinitely for the spin lock to be released, and then places it in the\r
  acquired state and returns SpinLock. All state transitions of SpinLock must\r
  be performed using MP safe mechanisms.\r
\r
  If SpinLock is NULL, then ASSERT().\r
  If SpinLock was not initialized with InitializeSpinLock(), then ASSERT().\r
  If PcdSpinLockTimeout is not zero, and SpinLock is can not be acquired in\r
  PcdSpinLockTimeout microseconds, then ASSERT().\r
\r
  @param  SpinLock  A pointer to the spin lock to place in the acquired state.\r
\r
  @return SpinLock\r
\r
**/\r
SPIN_LOCK *\r
EFIAPI\r
AcquireSpinLock (\r
  IN OUT  SPIN_LOCK                 *SpinLock\r
  )\r
{\r
  UINT64                            Tick;\r
  UINT64                            Start, End;\r
  UINT64                            Timeout;\r
\r
  Tick = 0;\r
  Start = 0;\r
  End = 0;\r
  if (PcdGet32 (PcdSpinLockTimeout) > 0) {\r
    Tick = GetPerformanceCounter ();\r
    Timeout = DivU64x32 (\r
                MultU64x32 (\r
                  GetPerformanceCounterProperties (&Start, &End),\r
                  PcdGet32 (PcdSpinLockTimeout)\r
                  ),\r
                1000000\r
                );\r
    if (Start < End) {\r
      Tick += Timeout;\r
    } else {\r
      Tick -= Timeout;\r
    }\r
  }\r
\r
  while (!AcquireSpinLockOrFail (SpinLock)) {\r
    CpuPause ();\r
    ASSERT ((Start < End) ^ (Tick <= GetPerformanceCounter ()));\r
  }\r
  return SpinLock;\r
}\r
\r
/**\r
  Attempts to place a spin lock in the acquired state.\r
\r
  This function checks the state of the spin lock specified by SpinLock. If\r
  SpinLock is in the released state, then this function places SpinLock in the\r
  acquired state and returns TRUE. Otherwise, FALSE is returned. All state\r
  transitions of SpinLock must be performed using MP safe mechanisms.\r
\r
  If SpinLock is NULL, then ASSERT().\r
  If SpinLock was not initialized with InitializeSpinLock(), then ASSERT().\r
\r
  @param  SpinLock  A pointer to the spin lock to place in the acquired state.\r
\r
  @retval TRUE  SpinLock was placed in the acquired state.\r
  @retval FALSE SpinLock could not be acquired.\r
\r
**/\r
BOOLEAN\r
EFIAPI\r
AcquireSpinLockOrFail (\r
  IN OUT  SPIN_LOCK                 *SpinLock\r
  )\r
{\r
  SPIN_LOCK    LockValue;\r
\r
  ASSERT (SpinLock != NULL);\r
\r
  LockValue = *SpinLock;\r
  ASSERT (LockValue == SPIN_LOCK_ACQUIRED || LockValue == SPIN_LOCK_RELEASED);\r
\r
  return (BOOLEAN)(\r
           InterlockedCompareExchangePointer (\r
             (VOID**)SpinLock,\r
             (VOID*)SPIN_LOCK_RELEASED,\r
             (VOID*)SPIN_LOCK_ACQUIRED\r
             ) == (VOID*)SPIN_LOCK_RELEASED\r
           );\r
}\r
\r
/**\r
  Releases a spin lock.\r
\r
  This function places the spin lock specified by SpinLock in the release state\r
  and returns SpinLock.\r
\r
  If SpinLock is NULL, then ASSERT().\r
  If SpinLock was not initialized with InitializeSpinLock(), then ASSERT().\r
\r
  @param  SpinLock  A pointer to the spin lock to release.\r
\r
  @return SpinLock\r
\r
**/\r
SPIN_LOCK *\r
EFIAPI\r
ReleaseSpinLock (\r
  IN OUT  SPIN_LOCK                 *SpinLock\r
  )\r
{\r
  SPIN_LOCK    LockValue;\r
\r
  ASSERT (SpinLock != NULL);\r
\r
  LockValue = *SpinLock;\r
  ASSERT (LockValue == SPIN_LOCK_ACQUIRED || LockValue == SPIN_LOCK_RELEASED);\r
\r
  *SpinLock = SPIN_LOCK_RELEASED;\r
  return SpinLock;\r
}\r
\r
/**\r
  Performs an atomic increment of an 32-bit unsigned integer.\r
\r
  Performs an atomic increment of the 32-bit unsigned integer specified by\r
  Value and returns the incremented value. The increment operation must be\r
  performed using MP safe mechanisms. The state of the return value is not\r
  guaranteed to be MP safe.\r
\r
  If Value is NULL, then ASSERT().\r
\r
  @param  Value A pointer to the 32-bit value to increment.\r
\r
  @return The incremented value.\r
\r
**/\r
UINT32\r
EFIAPI\r
InterlockedIncrement (\r
  IN      UINT32                    *Value\r
  )\r
{\r
  ASSERT (Value != NULL);\r
  return InternalSyncIncrement (Value);\r
}\r
\r
/**\r
  Performs an atomic decrement of an 32-bit unsigned integer.\r
\r
  Performs an atomic decrement of the 32-bit unsigned integer specified by\r
  Value and returns the decremented value. The decrement operation must be\r
  performed using MP safe mechanisms. The state of the return value is not\r
  guaranteed to be MP safe.\r
\r
  If Value is NULL, then ASSERT().\r
\r
  @param  Value A pointer to the 32-bit value to decrement.\r
\r
  @return The decremented value.\r
\r
**/\r
UINT32\r
EFIAPI\r
InterlockedDecrement (\r
  IN      UINT32                    *Value\r
  )\r
{\r
  ASSERT (Value != NULL);\r
  return InternalSyncDecrement (Value);\r
}\r
\r
/**\r
  Performs an atomic compare exchange operation on a 32-bit unsigned integer.\r
\r
  Performs an atomic compare exchange operation on the 32-bit unsigned integer\r
  specified by Value.  If Value is equal to CompareValue, then Value is set to \r
  ExchangeValue and CompareValue is returned.  If Value is not equal to CompareValue,\r
  then Value is returned.  The compare exchange operation must be performed using \r
  MP safe mechanisms.\r
\r
  If Value is NULL, then ASSERT().\r
\r
  @param  Value         A pointer to the 32-bit value for the compare exchange\r
                        operation.\r
  @param  CompareValue  32-bit value used in compare operation.\r
  @param  ExchangeValue 32-bit value used in exchange operation.\r
\r
  @return The original *Value before exchange.\r
\r
**/\r
UINT32\r
EFIAPI\r
InterlockedCompareExchange32 (\r
  IN OUT  UINT32                    *Value,\r
  IN      UINT32                    CompareValue,\r
  IN      UINT32                    ExchangeValue\r
  )\r
{\r
  ASSERT (Value != NULL);\r
  return InternalSyncCompareExchange32 (Value, CompareValue, ExchangeValue);\r
}\r
\r
/**\r
  Performs an atomic compare exchange operation on a 64-bit unsigned integer.\r
\r
  Performs an atomic compare exchange operation on the 64-bit unsigned integer specified \r
  by Value.  If Value is equal to CompareValue, then Value is set to ExchangeValue and \r
  CompareValue is returned.  If Value is not equal to CompareValue, then Value is returned. \r
  The compare exchange operation must be performed using MP safe mechanisms.\r
\r
  If Value is NULL, then ASSERT().\r
\r
  @param  Value         A pointer to the 64-bit value for the compare exchange\r
                        operation.\r
  @param  CompareValue  64-bit value used in compare operation.\r
  @param  ExchangeValue 64-bit value used in exchange operation.\r
\r
  @return The original *Value before exchange.\r
\r
**/\r
UINT64\r
EFIAPI\r
InterlockedCompareExchange64 (\r
  IN OUT  UINT64                    *Value,\r
  IN      UINT64                    CompareValue,\r
  IN      UINT64                    ExchangeValue\r
  )\r
{\r
  ASSERT (Value != NULL);\r
  return InternalSyncCompareExchange64 (Value, CompareValue, ExchangeValue);\r
}\r
\r
/**\r
  Performs an atomic compare exchange operation on a pointer value.\r
\r
  Performs an atomic compare exchange operation on the pointer value specified\r
  by Value. If Value is equal to CompareValue, then Value is set to\r
  ExchangeValue and CompareValue is returned. If Value is not equal to\r
  CompareValue, then Value is returned. The compare exchange operation must be\r
  performed using MP safe mechanisms.\r
\r
  If Value is NULL, then ASSERT().\r
\r
  @param  Value         A pointer to the pointer value for the compare exchange\r
                        operation.\r
  @param  CompareValue  Pointer value used in compare operation.\r
  @param  ExchangeValue Pointer value used in exchange operation.\r
\r
**/\r
VOID *\r
EFIAPI\r
InterlockedCompareExchangePointer (\r
  IN OUT  VOID                      **Value,\r
  IN      VOID                      *CompareValue,\r
  IN      VOID                      *ExchangeValue\r
  )\r
{\r
  UINT8  SizeOfValue;\r
\r
  SizeOfValue = sizeof (*Value);\r
\r
  switch (SizeOfValue) {\r
    case sizeof (UINT32):\r
      return (VOID*)(UINTN)InterlockedCompareExchange32 (\r
                             (UINT32*)Value,\r
                             (UINT32)(UINTN)CompareValue,\r
                             (UINT32)(UINTN)ExchangeValue\r
                             );\r
    case sizeof (UINT64):\r
      return (VOID*)(UINTN)InterlockedCompareExchange64 (\r
                             (UINT64*)Value,\r
                             (UINT64)(UINTN)CompareValue,\r
                             (UINT64)(UINTN)ExchangeValue\r
                             );\r
    default:\r
      ASSERT (FALSE);\r
      return NULL;\r
  }\r
}\r
Commit	Line	Data
a4e9aab9	1	/** @file\r
	2	Implementation of synchronization functions.\r
	3	\r
	4	Copyright (c) 2006, Intel Corporation<BR>\r
	5	All rights reserved. This program and the accompanying materials\r
	6	are licensed and made available under the terms and conditions of the BSD License\r
	7	which accompanies this distribution. The full text of the license may be found at\r
	8	http://opensource.org/licenses/bsd-license.php\r
	9	\r
	10	THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,\r
	11	WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.\r
	12	\r
	13	Module Name: Synchronization.c\r
	14	\r
	15	**/\r
	16	\r
	17	#include "BaseLibInternals.h"\r
	18	\r
55bfb04e	19	#define SPIN_LOCK_RELEASED ((UINTN) 1)\r
55bfb04e	20	#define SPIN_LOCK_ACQUIRED ((UINTN) 2)\r
a4e9aab9	21	\r
	22	/**\r
	23	Retrieves the architecture specific spin lock alignment requirements for\r
	24	optimal spin lock performance.\r
	25	\r
	26	This function retrieves the spin lock alignment requirements for optimal\r
	27	performance on a given CPU architecture. The spin lock alignment must be a\r
	28	power of two and is returned by this function. If there are no alignment\r
	29	requirements, then 1 must be returned. The spin lock synchronization\r
	30	functions must function correctly if the spin lock size and alignment values\r
	31	returned by this function are not used at all. These values are hints to the\r
	32	consumers of the spin lock synchronization functions to obtain optimal spin\r
	33	lock performance.\r
	34	\r
	35	@return The architecture specific spin lock alignment.\r
	36	\r
	37	**/\r
	38	UINTN\r
	39	EFIAPI\r
	40	GetSpinLockProperties (\r
	41	VOID\r
	42	)\r
	43	{\r
	44	// @bug May use a PCD entry to determine this alignment.\r
	45	return 32;\r
	46	}\r
	47	\r
	48	/**\r
	49	Initializes a spin lock to the released state and returns the spin lock.\r
	50	\r
	51	This function initializes the spin lock specified by SpinLock to the released\r
	52	state, and returns SpinLock. Optimal performance can be achieved by calling\r
	53	GetSpinLockProperties() to determine the size and alignment requirements for\r
	54	SpinLock.\r
	55	\r
	56	If SpinLock is NULL, then ASSERT().\r
	57	\r
	58	@param SpinLock A pointer to the spin lock to initialize to the released\r
	59	state.\r
	60	\r
	61	@return SpinLock\r
	62	\r
	63	**/\r
	64	SPIN_LOCK *\r
	65	EFIAPI\r
	66	InitializeSpinLock (\r
	67	OUT SPIN_LOCK *SpinLock\r
	68	)\r
	69	{\r
	70	ASSERT (SpinLock != NULL);\r
	71	*SpinLock = SPIN_LOCK_RELEASED;\r
	72	return SpinLock;\r
	73	}\r
	74	\r
	75	/**\r
	76	Waits until a spin lock can be placed in the acquired state.\r
	77	\r
	78	This function checks the state of the spin lock specified by SpinLock. If\r
	79	SpinLock is in the released state, then this function places SpinLock in the\r
	80	acquired state and returns SpinLock. Otherwise, this function waits\r
	81	indefinitely for the spin lock to be released, and then places it in the\r
	82	acquired state and returns SpinLock. All state transitions of SpinLock must\r
	83	be performed using MP safe mechanisms.\r
	84	\r
85	If SpinLock is NULL, then ASSERT().\r
86	If SpinLock was not initialized with InitializeSpinLock(), then ASSERT().\r
87	If PcdSpinLockTimeout is not zero, and SpinLock is can not be acquired in\r
88	PcdSpinLockTimeout microseconds, then ASSERT().\r
89	\r
90	@param SpinLock A pointer to the spin lock to place in the acquired state.\r
91	\r
92	@return SpinLock\r
93	\r
94	**/\r
95	SPIN_LOCK *\r
96	EFIAPI\r
97	AcquireSpinLock (\r
98	IN OUT SPIN_LOCK *SpinLock\r
99	)\r
100	{\r
101	UINT64 Tick;\r
102	UINT64 Start, End;\r
103	UINT64 Timeout;\r
104	\r
105	Tick = 0;\r
106	Start = 0;\r
107	End = 0;\r
108	if (PcdGet32 (PcdSpinLockTimeout) > 0) {\r
109	Tick = GetPerformanceCounter ();\r
110	Timeout = DivU64x32 (\r
111	MultU64x32 (\r
112	GetPerformanceCounterProperties (&Start, &End),\r
113	PcdGet32 (PcdSpinLockTimeout)\r
114	),\r
115	1000000\r
116	);\r
117	if (Start < End) {\r
118	Tick += Timeout;\r
119	} else {\r
120	Tick -= Timeout;\r
121	}\r
122	}\r
123	\r
124	while (!AcquireSpinLockOrFail (SpinLock)) {\r
125	CpuPause ();\r
126	ASSERT ((Start < End) ^ (Tick <= GetPerformanceCounter ()));\r
127	}\r
128	return SpinLock;\r
129	}\r
130	\r
131	/**\r
132	Attempts to place a spin lock in the acquired state.\r
133	\r
134	This function checks the state of the spin lock specified by SpinLock. If\r
135	SpinLock is in the released state, then this function places SpinLock in the\r
136	acquired state and returns TRUE. Otherwise, FALSE is returned. All state\r
137	transitions of SpinLock must be performed using MP safe mechanisms.\r
138	\r
139	If SpinLock is NULL, then ASSERT().\r
140	If SpinLock was not initialized with InitializeSpinLock(), then ASSERT().\r
141	\r
142	@param SpinLock A pointer to the spin lock to place in the acquired state.\r
143	\r
144	@retval TRUE SpinLock was placed in the acquired state.\r
145	@retval FALSE SpinLock could not be acquired.\r
146	\r
147	**/\r
148	BOOLEAN\r
149	EFIAPI\r
150	AcquireSpinLockOrFail (\r
151	IN OUT SPIN_LOCK *SpinLock\r
152	)\r
153	{\r
154	SPIN_LOCK LockValue;\r
155	\r
156	ASSERT (SpinLock != NULL);\r
157	\r
158	LockValue = *SpinLock;\r
159	ASSERT (LockValue == SPIN_LOCK_ACQUIRED \|\| LockValue == SPIN_LOCK_RELEASED);\r
160	\r
161	return (BOOLEAN)(\r
162	InterlockedCompareExchangePointer (\r
163	(VOID**)SpinLock,\r
164	(VOID*)SPIN_LOCK_RELEASED,\r
165	(VOID*)SPIN_LOCK_ACQUIRED\r
166	) == (VOID*)SPIN_LOCK_RELEASED\r
167	);\r
168	}\r
169	\r
170	/**\r
171	Releases a spin lock.\r
172	\r
173	This function places the spin lock specified by SpinLock in the release state\r
174	and returns SpinLock.\r
175	\r
176	If SpinLock is NULL, then ASSERT().\r
177	If SpinLock was not initialized with InitializeSpinLock(), then ASSERT().\r
178	\r
179	@param SpinLock A pointer to the spin lock to release.\r
180	\r
181	@return SpinLock\r
182	\r
183	**/\r
184	SPIN_LOCK *\r
185	EFIAPI\r
186	ReleaseSpinLock (\r
187	IN OUT SPIN_LOCK *SpinLock\r
188	)\r
189	{\r
190	SPIN_LOCK LockValue;\r
191	\r
192	ASSERT (SpinLock != NULL);\r
193	\r
194	LockValue = *SpinLock;\r
195	ASSERT (LockValue == SPIN_LOCK_ACQUIRED \|\| LockValue == SPIN_LOCK_RELEASED);\r
196	\r
197	*SpinLock = SPIN_LOCK_RELEASED;\r
198	return SpinLock;\r
199	}\r
200	\r
201	/**\r
202	Performs an atomic increment of an 32-bit unsigned integer.\r
203	\r
204	Performs an atomic increment of the 32-bit unsigned integer specified by\r
205	Value and returns the incremented value. The increment operation must be\r
206	performed using MP safe mechanisms. The state of the return value is not\r
207	guaranteed to be MP safe.\r
208	\r
209	If Value is NULL, then ASSERT().\r
210	\r
211	@param Value A pointer to the 32-bit value to increment.\r
212	\r
213	@return The incremented value.\r
214	\r
215	**/\r
216	UINT32\r
217	EFIAPI\r
218	InterlockedIncrement (\r
219	IN UINT32 *Value\r
220	)\r
221	{\r
222	ASSERT (Value != NULL);\r
223	return InternalSyncIncrement (Value);\r
224	}\r
225	\r
226	/**\r
227	Performs an atomic decrement of an 32-bit unsigned integer.\r
228	\r
229	Performs an atomic decrement of the 32-bit unsigned integer specified by\r
230	Value and returns the decremented value. The decrement operation must be\r
231	performed using MP safe mechanisms. The state of the return value is not\r
232	guaranteed to be MP safe.\r
233	\r
234	If Value is NULL, then ASSERT().\r
235	\r
236	@param Value A pointer to the 32-bit value to decrement.\r
237	\r
238	@return The decremented value.\r
239	\r
240	**/\r
241	UINT32\r
242	EFIAPI\r
243	InterlockedDecrement (\r
244	IN UINT32 *Value\r
245	)\r
246	{\r
247	ASSERT (Value != NULL);\r
248	return InternalSyncDecrement (Value);\r
249	}\r
250	\r
251	/**\r
252	Performs an atomic compare exchange operation on a 32-bit unsigned integer.\r
253	\r
254	Performs an atomic compare exchange operation on the 32-bit unsigned integer\r
255	specified by Value. If Value is equal to CompareValue, then Value is set to \r
256	ExchangeValue and CompareValue is returned. If Value is not equal to CompareValue,\r
257	then Value is returned. The compare exchange operation must be performed using \r
258	MP safe mechanisms.\r
259	\r
260	If Value is NULL, then ASSERT().\r
261	\r
262	@param Value A pointer to the 32-bit value for the compare exchange\r
263	operation.\r
264	@param CompareValue 32-bit value used in compare operation.\r
265	@param ExchangeValue 32-bit value used in exchange operation.\r
266	\r
267	@return The original *Value before exchange.\r
268	\r
269	**/\r
270	UINT32\r
271	EFIAPI\r
272	InterlockedCompareExchange32 (\r
273	IN OUT UINT32 *Value,\r
274	IN UINT32 CompareValue,\r
275	IN UINT32 ExchangeValue\r
276	)\r
277	{\r
278	ASSERT (Value != NULL);\r
279	return InternalSyncCompareExchange32 (Value, CompareValue, ExchangeValue);\r
280	}\r
281	\r
282	/**\r
283	Performs an atomic compare exchange operation on a 64-bit unsigned integer.\r
284	\r
285	Performs an atomic compare exchange operation on the 64-bit unsigned integer specified \r
286	by Value. If Value is equal to CompareValue, then Value is set to ExchangeValue and \r
287	CompareValue is returned. If Value is not equal to CompareValue, then Value is returned. \r
288	The compare exchange operation must be performed using MP safe mechanisms.\r
289	\r
290	If Value is NULL, then ASSERT().\r
291	\r
292	@param Value A pointer to the 64-bit value for the compare exchange\r
293	operation.\r
294	@param CompareValue 64-bit value used in compare operation.\r
295	@param ExchangeValue 64-bit value used in exchange operation.\r
296	\r
297	@return The original *Value before exchange.\r
298	\r
299	**/\r
300	UINT64\r
301	EFIAPI\r
302	InterlockedCompareExchange64 (\r
303	IN OUT UINT64 *Value,\r
304	IN UINT64 CompareValue,\r
305	IN UINT64 ExchangeValue\r
306	)\r
307	{\r
308	ASSERT (Value != NULL);\r
309	return InternalSyncCompareExchange64 (Value, CompareValue, ExchangeValue);\r
310	}\r
311	\r
312	/**\r
313	Performs an atomic compare exchange operation on a pointer value.\r
314	\r
315	Performs an atomic compare exchange operation on the pointer value specified\r
316	by Value. If Value is equal to CompareValue, then Value is set to\r
317	ExchangeValue and CompareValue is returned. If Value is not equal to\r
318	CompareValue, then Value is returned. The compare exchange operation must be\r
319	performed using MP safe mechanisms.\r
320	\r
321	If Value is NULL, then ASSERT().\r
322	\r
323	@param Value A pointer to the pointer value for the compare exchange\r
324	operation.\r
325	@param CompareValue Pointer value used in compare operation.\r
326	@param ExchangeValue Pointer value used in exchange operation.\r
327	\r
328	**/\r
329	VOID *\r
330	EFIAPI\r
331	InterlockedCompareExchangePointer (\r
332	IN OUT VOID **Value,\r
333	IN VOID *CompareValue,\r
334	IN VOID *ExchangeValue\r
335	)\r
336	{\r
337	UINT8 SizeOfValue;\r
338	\r
339	SizeOfValue = sizeof (*Value);\r
340	\r
341	switch (SizeOfValue) {\r
342	case sizeof (UINT32):\r
343	return (VOID*)(UINTN)InterlockedCompareExchange32 (\r
344	(UINT32*)Value,\r
345	(UINT32)(UINTN)CompareValue,\r
346	(UINT32)(UINTN)ExchangeValue\r
347	);\r
348	case sizeof (UINT64):\r
349	return (VOID*)(UINTN)InterlockedCompareExchange64 (\r
350	(UINT64*)Value,\r
351	(UINT64)(UINTN)CompareValue,\r
352	(UINT64)(UINTN)ExchangeValue\r
353	);\r
354	default:\r
355	ASSERT (FALSE);\r
356	return NULL;\r
357	}\r
358	}\r