[176] | 1 | /* |
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| 2 | * swift_deque.c |
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| 3 | * |
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| 4 | * (c) 2009 Ionut Rosoiu <ionut.rosoiu@gmail.com> |
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| 5 | * |
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| 6 | */ |
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| 7 | |
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| 8 | #include "swift_deque.h" |
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| 9 | #include <stdio.h> |
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| 10 | |
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| 11 | void swift_deque_init(swift_thread_t *thread, swift_deque_t *q, swift_size_t size) { |
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| 12 | //automatically resized to a power of two |
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| 13 | //SWIFT_CHECK(size & (size-1), SWIFT_RETURN_WITH_STATUS(SWIFT_INVALID_PARAM)); |
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| 14 | |
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| 15 | if (size & (size-1)) { |
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| 16 | /* round up to a power of two */ |
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| 17 | swift_size_t newSize = 1; |
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| 18 | |
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| 19 | while (size) { |
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| 20 | size >>= 1; |
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| 21 | newSize <<= 1; |
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| 22 | } |
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| 23 | |
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| 24 | size = newSize; |
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| 25 | } |
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| 26 | |
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| 27 | q->size = size; |
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| 28 | q->size_mask = size - 1; |
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| 29 | q->top = q->bottom = q->top_cached = 0; |
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| 30 | q->elements = (swift_frame_t**) swift_malloc(thread, size * sizeof(swift_frame_t*)); |
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| 31 | } |
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| 32 | |
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| 33 | void swift_deque_push(swift_deque_t *q, swift_frame_t *frame, swift_status_t *status) { |
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| 34 | swift_dword_t t, b; |
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| 35 | SWIFT_CHECK(NULL != q, SWIFT_RETURN_WITH_STATUS(SWIFT_INVALID_PARAM)); |
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| 36 | |
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| 37 | b = q->bottom; |
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| 38 | /* avoid some cache misses by using this local variable */ |
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| 39 | t = q->top_cached; |
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| 40 | |
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| 41 | if (b - t >= q->size_mask) { /* size_mask = size - 1 */ |
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| 42 | /* because we've used a cached value, we might have a false positive */ |
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| 43 | t = q->top; |
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| 44 | q->top_cached = t; |
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| 45 | |
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| 46 | if (b - t >= q->size_mask) { |
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| 47 | //TODO: handle reallocation (...and ALL the problems that come along...) |
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| 48 | // for the moment fail this case |
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| 49 | *status = SWIFT_DEQUE_FULL; |
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| 50 | return; |
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| 51 | } |
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| 52 | } |
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| 53 | |
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| 54 | /* push the new value at the bottom */ |
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| 55 | q->elements[b & q->size_mask] = frame; |
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| 56 | q->bottom = b + 1; |
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| 57 | |
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| 58 | *status = SWIFT_SUCCESS; |
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| 59 | } |
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| 60 | |
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| 61 | swift_frame_t* swift_deque_pop(swift_deque_t *q, swift_status_t *status) { |
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| 62 | swift_frame_t *ret = NULL; |
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| 63 | swift_dword_t b, t; |
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| 64 | long size; |
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| 65 | |
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| 66 | SWIFT_CHECK(NULL != q, *status = SWIFT_INVALID_PARAM; return NULL); |
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| 67 | |
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| 68 | b = q->bottom; |
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| 69 | |
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| 70 | b--; |
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| 71 | q->bottom = b; |
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| 72 | |
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| 73 | /* top must be read _after_ bottom is written (i.e. incremented) */ |
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| 74 | swift_memory_write_barrier(); |
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| 75 | |
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| 76 | t = q->top; |
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| 77 | q->top_cached = t; |
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| 78 | |
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| 79 | size = (long)(b - t); |
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| 80 | |
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| 81 | if (size < 0) { |
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| 82 | q->bottom = t; |
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| 83 | |
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| 84 | *status = SWIFT_DEQUE_EMPTY; |
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| 85 | return NULL; |
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| 86 | } |
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| 87 | |
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| 88 | /* get a reference to the element to return */ |
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| 89 | ret = q->elements[b & q->size_mask]; |
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| 90 | |
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| 91 | /* enough active elements left in the array */ |
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| 92 | if (size > 0) { |
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| 93 | return ret; |
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| 94 | } |
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| 95 | |
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| 96 | /* check to see if the last element was concurrently stolen */ |
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| 97 | if (! SWIFT_CAS(q->top, t, t+1)) { |
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| 98 | /* someone has stolen our element */ |
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| 99 | *status = SWIFT_DEQUE_EMPTY; |
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| 100 | ret = NULL; |
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| 101 | } |
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| 102 | |
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| 103 | /* the array is empty and q->top is t+1; adjust bottom */ |
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| 104 | q->bottom = t + 1; |
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| 105 | q->top_cached = t + 1; |
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| 106 | |
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| 107 | return ret; |
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| 108 | } |
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| 109 | |
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| 110 | swift_frame_t* swift_deque_steal(swift_deque_t *q, swift_status_t *status) { |
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| 111 | swift_dword_t t, b; |
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| 112 | swift_frame_t *ret = NULL; |
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| 113 | |
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| 114 | SWIFT_CHECK(NULL != q, *status = SWIFT_INVALID_PARAM; return NULL); |
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| 115 | |
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| 116 | t = q->top; |
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| 117 | |
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| 118 | /* a read barrier is needed to guarantee a consistent view of the memory |
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| 119 | * see also the write_barrier() in the pop() |
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| 120 | */ |
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| 121 | swift_memory_read_barrier(); |
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| 122 | |
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| 123 | b = q->bottom; |
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| 124 | |
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| 125 | if ((long)(b - t) <= 0) { |
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| 126 | *status = SWIFT_DEQUE_EMPTY; |
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| 127 | return NULL; |
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| 128 | } |
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| 129 | |
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| 130 | /* get a reference to the element _before_ trying the CAS |
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| 131 | * (i.e. _before_ checking we've won the race); |
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| 132 | * if not, in case we win, we might get a reference to a newly |
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| 133 | * push()-ed element instead of the current one |
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| 134 | */ |
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| 135 | ret = q->elements[t & q->size_mask]; |
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| 136 | |
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| 137 | if (! SWIFT_CAS(q->top, t, t+1)) { |
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| 138 | *status = SWIFT_DEQUE_ABORT; |
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| 139 | return NULL; |
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| 140 | } |
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| 141 | |
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| 142 | *status = SWIFT_SUCCESS; |
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| 143 | return ret; |
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| 144 | } |
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| 145 | |
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| 146 | void swift_deque_destroy(swift_thread_t *thread, swift_deque_t *q) { |
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| 147 | swift_free(thread, q->elements); |
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| 148 | } |
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