1 /* -*- Mode: C; c-basic-offset:4 ; indent-tabs-mode:nil ; -*- */
4 * (C) 2003 by Argonne National Laboratory.
5 * See COPYRIGHT in top-level directory.
8 /* MPI-3 distributed linked list construction example
9 * --------------------------------------------------
11 * Construct a distributed shared linked list using proposed MPI-3 dynamic
12 * windows. Initially process 0 creates the head of the list, attaches it to
13 * the window, and broadcasts the pointer to all processes. All processes then
14 * concurrently append N new elements to the list. When a process attempts to
15 * attach its element to the tail of list it may discover that its tail pointer
16 * is stale and it must chase ahead to the new tail before the element can be
32 #define ELEM_PER_ROW 16
34 /* Linked list pointer */
40 /* Linked list element */
46 static const llist_ptr_t nil = { -1, (MPI_Aint) MPI_BOTTOM };
47 static const int verbose = 0;
49 /* List of locally allocated list elements. */
50 static llist_elem_t **my_elems = NULL;
51 static int my_elems_size = 0;
52 static int my_elems_count = 0;
54 /* Allocate a new shared linked list element */
55 MPI_Aint alloc_elem(int value, MPI_Win win) {
57 llist_elem_t *elem_ptr;
59 /* Allocate the new element and register it with the window */
60 MPI_Alloc_mem(sizeof(llist_elem_t), MPI_INFO_NULL, &elem_ptr);
61 elem_ptr->value = value;
63 MPI_Win_attach(win, elem_ptr, sizeof(llist_elem_t));
65 /* Add the element to the list of local elements so we can free it later. */
66 if (my_elems_size == my_elems_count) {
68 my_elems = realloc(my_elems, my_elems_size*sizeof(void*));
70 my_elems[my_elems_count] = elem_ptr;
73 MPI_Get_address(elem_ptr, &disp);
77 int main(int argc, char **argv) {
80 llist_ptr_t head_ptr, tail_ptr;
82 MPI_Init(&argc, &argv);
84 MPI_Comm_rank(MPI_COMM_WORLD, &procid);
85 MPI_Comm_size(MPI_COMM_WORLD, &nproc);
87 MPI_Win_create_dynamic(MPI_INFO_NULL, MPI_COMM_WORLD, &llist_win);
89 /* Process 0 creates the head node */
91 head_ptr.disp = alloc_elem(-1, llist_win);
93 /* Broadcast the head pointer to everyone */
95 MPI_Bcast(&head_ptr.disp, 1, MPI_AINT, 0, MPI_COMM_WORLD);
98 /* All processes concurrently append NUM_ELEMS elements to the list */
99 for (i = 0; i < NUM_ELEMS; i++) {
100 llist_ptr_t new_elem_ptr;
103 /* Create a new list element and register it with the window */
104 new_elem_ptr.rank = procid;
105 new_elem_ptr.disp = alloc_elem(procid, llist_win);
107 /* Append the new node to the list. This might take multiple attempts if
108 others have already appended and our tail pointer is stale. */
110 llist_ptr_t next_tail_ptr = nil;
112 MPI_Win_lock(MPI_LOCK_EXCLUSIVE, tail_ptr.rank, 0, llist_win);
114 MPI_Compare_and_swap((void*) &new_elem_ptr.rank, (void*) &nil.rank,
115 (void*) &next_tail_ptr.rank, MPI_INT, tail_ptr.rank,
116 (MPI_Aint) &(((llist_elem_t*)tail_ptr.disp)->next.rank), llist_win);
118 MPI_Win_unlock(tail_ptr.rank, llist_win);
119 success = (next_tail_ptr.rank == nil.rank);
124 MPI_Win_lock(MPI_LOCK_EXCLUSIVE, tail_ptr.rank, 0, llist_win);
126 MPI_Put(&new_elem_ptr.disp, 1, MPI_AINT, tail_ptr.rank,
127 (MPI_Aint) &(((llist_elem_t*)tail_ptr.disp)->next.disp), 1,
128 MPI_AINT, llist_win);
130 MPI_Win_unlock(tail_ptr.rank, llist_win);
131 tail_ptr = new_elem_ptr;
133 /* For implementations that use pt-to-pt messaging, force progress for other threads'
135 for (i = 0; i < NPROBE; i++)
136 MPI_Iprobe(MPI_ANY_SOURCE, MPI_ANY_TAG, MPI_COMM_WORLD, &flag, MPI_STATUS_IGNORE);
139 /* Tail pointer is stale, fetch the displacement. May take multiple tries
140 if it is being updated. */
142 MPI_Win_lock(MPI_LOCK_EXCLUSIVE, tail_ptr.rank, 0, llist_win);
144 MPI_Get( &next_tail_ptr.disp, 1, MPI_AINT, tail_ptr.rank,
145 (MPI_Aint) &(((llist_elem_t*)tail_ptr.disp)->next.disp),
146 1, MPI_AINT, llist_win);
148 MPI_Win_unlock(tail_ptr.rank, llist_win);
149 } while (next_tail_ptr.disp == nil.disp);
150 tail_ptr = next_tail_ptr;
155 MPI_Barrier(MPI_COMM_WORLD);
157 /* Traverse the list and verify that all processes inserted exactly the correct
158 number of elements. */
162 int *counts, count = 0;
164 counts = (int*) malloc(sizeof(int) * nproc);
165 assert(counts != NULL);
167 for (i = 0; i < nproc; i++)
172 /* Walk the list and tally up the number of elements inserted by each rank */
173 while (tail_ptr.disp != nil.disp) {
176 MPI_Win_lock(MPI_LOCK_EXCLUSIVE, tail_ptr.rank, 0, llist_win);
178 MPI_Get(&elem, sizeof(llist_elem_t), MPI_BYTE,
179 tail_ptr.rank, tail_ptr.disp, sizeof(llist_elem_t), MPI_BYTE, llist_win);
181 MPI_Win_unlock(tail_ptr.rank, llist_win);
183 tail_ptr = elem.next;
185 /* This is not the root */
187 assert(elem.value >= 0 && elem.value < nproc);
188 counts[elem.value]++;
192 int last_elem = tail_ptr.disp == nil.disp;
193 printf("%2d%s", elem.value, last_elem ? "" : " -> ");
194 if (count % ELEM_PER_ROW == 0 && !last_elem)
199 /* This is the root */
201 assert(elem.value == -1);
209 /* Verify the counts we collected */
210 for (i = 0; i < nproc; i++) {
211 int expected = NUM_ELEMS;
213 if (counts[i] != expected) {
214 printf("Error: Rank %d inserted %d elements, expected %d\n", i, counts[i], expected);
219 printf("%s\n", errors == 0 ? " No Errors" : "FAIL");
223 MPI_Win_free(&llist_win);
225 /* Free all the elements in the list */
226 for ( ; my_elems_count > 0; my_elems_count--)
227 MPI_Free_mem(my_elems[my_elems_count-1]);