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/*
* Copyright (c) 2005 Hewlett-Packard Development Company, L.P.
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
/*
* The implementation of the routines described here is covered by the GPL.
* This header file is covered by the above license.
*/
/* Almost lock-free LIFO linked lists (linked stacks). */
#ifndef AO_STACK_H
#define AO_STACK_H
#include "atomic_ops.h"
#ifndef AO_HAVE_double_t
/* Can happen if we are using CAS emulation, since we do not want to */
/* force that here, in case other atomic_ops clients do not want it. */
# include "atomic_ops/sysdeps/standard_ao_double_t.h"
#endif
#ifdef __cplusplus
extern "C" {
#endif
#ifdef AO_USE_ALMOST_LOCK_FREE
/* Use the almost-non-blocking implementation regardless of the */
/* double-word CAS availability. */
#elif !defined(AO_HAVE_compare_double_and_swap_double) \
&& !defined(AO_HAVE_compare_double_and_swap) \
&& defined(AO_HAVE_compare_and_swap)
# define AO_USE_ALMOST_LOCK_FREE
#else
/* If we have no compare-and-swap operation defined, we assume */
/* that we will actually be using CAS emulation. If we do that, */
/* it's cheaper to use the version-based implementation. */
# define AO_STACK_IS_LOCK_FREE
#endif
/*
* These are not guaranteed to be completely lock-free.
* List insertion may spin under extremely unlikely conditions.
* It cannot deadlock due to recursive reentry unless AO_list_remove
* is called while at least AO_BL_SIZE activations of
* AO_list_remove are currently active in the same thread, i.e.
* we must have at least AO_BL_SIZE recursive signal handler
* invocations.
*
* All operations take an AO_list_aux argument. It is safe to
* share a single AO_list_aux structure among all lists, but that
* may increase contention. Any given list must always be accessed
* with the same AO_list_aux structure.
*
* We make some machine-dependent assumptions:
* - We have a compare-and-swap operation.
* - At least _AO_N_BITS low order bits in pointers are
* zero and normally unused.
* - size_t and pointers have the same size.
*
* We do use a fully lock-free implementation if double-width
* compare-and-swap operations are available.
*/
/* AO_stack_aux should be treated as opaque. It is fully defined */
/* here, so it can be allocated, and also to facilitate debugging. */
/* Note: changing the value of AO_BL_SIZE leads to the ABI change. */
#ifndef AO_BL_SIZE
# define AO_BL_SIZE 2
#endif
/* The number of low order pointer bits we can use for a small */
/* version number. */
#if defined(__LP64__) || defined(_LP64) || defined(_WIN64)
# define AO_N_BITS 3
#else
# define AO_N_BITS 2
#endif
#define AO_BIT_MASK ((1 << AO_N_BITS) - 1)
#if AO_BL_SIZE > (1 << AO_N_BITS)
# error AO_BL_SIZE too big
#endif
typedef struct AO__stack_aux {
volatile AO_t AO_stack_bl[AO_BL_SIZE];
} AO_stack_aux;
struct AO__stack_ptr_aux {
volatile AO_t AO_ptr;
AO_stack_aux AO_aux;
};
/* The AO stack type. Should be treated as opaque. */
/* Note: AO_stack_t variables are not intended to be local ones, */
/* otherwise it is the client responsibility to ensure they have */
/* double-word alignment. */
typedef union AO__stack {
struct AO__stack_ptr_aux AO_pa;
volatile AO_double_t AO_vp;
} AO_stack_t;
/* The static initializer of the AO stack type. */
#define AO_STACK_INITIALIZER { /* .AO_pa= */ { 0, { {0} } } }
#ifdef AO_USE_ALMOST_LOCK_FREE
/* The following two routines should not normally be used directly. */
/* We make them visible here for the rare cases in which it makes */
/* sense to share the AO_stack_aux between stacks. */
AO_API void
AO_stack_push_explicit_aux_release(volatile AO_t *list, AO_t *new_element,
AO_stack_aux *);
AO_API AO_t *
AO_stack_pop_explicit_aux_acquire(volatile AO_t *list, AO_stack_aux *);
#endif /* AO_USE_ALMOST_LOCK_FREE */
#ifndef AO_REAL_PTR_AS_MACRO
/* The stack implementation knows only about the location of */
/* link fields in nodes, and nothing about the rest of the */
/* stack elements. Link fields hold an AO_t, which is not */
/* necessarily a real pointer. This converts the AO_t to a */
/* real (AO_t *) which is either NULL, or points at the link */
/* field in the next node. */
# define AO_REAL_NEXT_PTR(x) AO_stack_next_ptr(x)
/* Convert an AO_stack_t to a pointer to the link field in */
/* the first element. */
# define AO_REAL_HEAD_PTR(x) AO_stack_head_ptr(&(x))
#elif defined(AO_USE_ALMOST_LOCK_FREE)
# define AO_REAL_NEXT_PTR(x) (AO_t *)((x) & ~AO_BIT_MASK)
# define AO_REAL_HEAD_PTR(x) AO_REAL_NEXT_PTR((x).AO_pa.AO_ptr)
#else
# define AO_REAL_NEXT_PTR(x) (AO_t *)(x)
# define AO_REAL_HEAD_PTR(x) (AO_t *)((x).AO_vp.AO_val2 /* ptr */)
#endif /* AO_REAL_PTR_AS_MACRO && !AO_USE_ALMOST_LOCK_FREE */
AO_API void AO_stack_push_release(AO_stack_t *list, AO_t *new_element);
#define AO_HAVE_stack_push_release
#define AO_stack_push(l, e) AO_stack_push_release(l, e)
#define AO_HAVE_stack_push
AO_API AO_t *AO_stack_pop_acquire(AO_stack_t *list);
#define AO_HAVE_stack_pop_acquire
#define AO_stack_pop(l) AO_stack_pop_acquire(l)
#define AO_HAVE_stack_pop
AO_API void AO_stack_init(AO_stack_t *list);
AO_API int AO_stack_is_lock_free(void);
AO_API AO_t *AO_stack_head_ptr(const AO_stack_t *list);
AO_API AO_t *AO_stack_next_ptr(AO_t /* next */);
#ifdef __cplusplus
} /* extern "C" */
#endif
#endif /* !AO_STACK_H */
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