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opal_atomic_lifo.h
1 /*
2 * Copyright (c) 2004-2005 The Trustees of Indiana University and Indiana
3 * University Research and Technology
4 * Corporation. All rights reserved.
5 * Copyright (c) 2004-2007 The University of Tennessee and The University
6 * of Tennessee Research Foundation. All rights
7 * reserved.
8 * Copyright (c) 2004-2005 High Performance Computing Center Stuttgart,
9 * University of Stuttgart. All rights reserved.
10 * Copyright (c) 2004-2005 The Regents of the University of California.
11 * All rights reserved.
12 * Copyright (c) 2007 Voltaire All rights reserved.
13 * Copyright (c) 2010 IBM Corporation. All rights reserved.
14 * $COPYRIGHT$
15 *
16 * Additional copyrights may follow
17 *
18 * $HEADER$
19 */
20
21 #ifndef OPAL_ATOMIC_LIFO_H_HAS_BEEN_INCLUDED
22 #define OPAL_ATOMIC_LIFO_H_HAS_BEEN_INCLUDED
23
24 #include "opal_config.h"
25 #include "opal/class/opal_list.h"
26
27 #if OPAL_ENABLE_MULTI_THREADS
28 #include "opal/sys/atomic.h"
29 #endif /* OPAL_ENABLE_MULTI_THREADS */
30
31 BEGIN_C_DECLS
32
33 /* Atomic Last In First Out lists. If we are in a multi-threaded environment then the
34 * atomicity is insured via the compare-and-swap operation, if not we simply do a read
35 * and/or a write.
36 *
37 * There is a trick. The ghost element at the end of the list. This ghost element has
38 * the next pointer pointing to itself, therefore we cannot go past the end of the list.
39 * With this approach we will never have a NULL element in the list, so we never have
40 * to test for the NULL.
41 */
42 struct opal_atomic_lifo_t
43 {
44 opal_object_t super;
45 opal_list_item_t* opal_lifo_head;
46 opal_list_item_t opal_lifo_ghost;
47 };
48
49 typedef struct opal_atomic_lifo_t opal_atomic_lifo_t;
50
51 OPAL_DECLSPEC OBJ_CLASS_DECLARATION(opal_atomic_lifo_t);
52
53
54 /* The ghost pointer will never change. The head will change via an atomic
55 * compare-and-swap. On most architectures the reading of a pointer is an
56 * atomic operation so we don't have to protect it.
57 */
58 static inline bool opal_atomic_lifo_is_empty( opal_atomic_lifo_t* lifo )
59 {
60 return (lifo->opal_lifo_head == &(lifo->opal_lifo_ghost) ? true : false);
61 }
62
63
64 /* Add one element to the LIFO. We will return the last head of the list
65 * to allow the upper level to detect if this element is the first one in the
66 * list (if the list was empty before this operation).
67 */
68 static inline opal_list_item_t* opal_atomic_lifo_push( opal_atomic_lifo_t* lifo,
69 opal_list_item_t* item )
70 {
71 #if OPAL_ENABLE_MULTI_THREADS
72 do {
73 item->opal_list_next = lifo->opal_lifo_head;
74 opal_atomic_wmb();
75 if( opal_atomic_cmpset_ptr( &(lifo->opal_lifo_head),
76 (void*)item->opal_list_next,
77 item ) ) {
78 opal_atomic_cmpset_32((volatile int32_t*)&item->item_free, 1, 0);
79 return (opal_list_item_t*)item->opal_list_next;
80 }
81 /* DO some kind of pause to release the bus */
82 } while( 1 );
83 #else
84 item->opal_list_next = lifo->opal_lifo_head;
85 lifo->opal_lifo_head = item;
86 return (opal_list_item_t*)item->opal_list_next;
87 #endif /* OPAL_ENABLE_MULTI_THREADS */
88 }
89
90 /* Retrieve one element from the LIFO. If we reach the ghost element then the LIFO
91 * is empty so we return NULL.
92 */
93 static inline opal_list_item_t* opal_atomic_lifo_pop( opal_atomic_lifo_t* lifo )
94 {
95 opal_list_item_t* item;
96 #if OPAL_ENABLE_MULTI_THREADS
97 while((item = lifo->opal_lifo_head) != &(lifo->opal_lifo_ghost))
98 {
99 opal_atomic_rmb();
100 if(!opal_atomic_cmpset_32((volatile int32_t*)&item->item_free, 0, 1))
101 continue;
102 if( opal_atomic_cmpset_ptr( &(lifo->opal_lifo_head),
103 item,
104 (void*)item->opal_list_next ) )
105 break;
106 opal_atomic_cmpset_32((volatile int32_t*)&item->item_free, 1, 0);
107 /* Do some kind of pause to release the bus */
108 }
109 #else
110 item = lifo->opal_lifo_head;
111 lifo->opal_lifo_head = (opal_list_item_t*)item->opal_list_next;
112 #endif /* OPAL_ENABLE_MULTI_THREADS */
113 if( item == &(lifo->opal_lifo_ghost) ) return NULL;
114 item->opal_list_next = NULL;
115 return item;
116 }
117
118 END_C_DECLS
119
120 #endif /* OPAL_ATOMIC_LIFO_H_HAS_BEEN_INCLUDED */
121
opal_list_item_t::opal_list_next
volatile struct opal_list_item_t * opal_list_next
Pointer to next list item.
Definition: opal_list.h:102
opal_atomic_rmb
void opal_atomic_rmb(void)
Read memory barrier.
opal_list.h
The opal_list_t interface is used to provide a generic doubly-linked list container for Open MPI...
opal_atomic_lifo_t
Definition: opal_atomic_lifo.h:42
opal_list_item_t
Definition: opal_list.h:98
opal_object_t
Base object.
Definition: opal_object.h:182
opal_atomic_wmb
void opal_atomic_wmb(void)
Write memory barrier.
atomic.h
Atomic operations.
OBJ_CLASS_DECLARATION
#define OBJ_CLASS_DECLARATION(NAME)
Declaration for class descriptor.
Definition: opal_object.h:236