void* scan_nodes(void* threadid) {
int i, j, k;
long tid;
unsigned int min_nbr_height;
Edge nbr_edge, min_height_edge;
long d;
long local_e;
long local_c;
int max_flow;
int isInQ;
int height_before_lift;
int node_push_times = 0, node_lift_times = 0;
int op_times = 0;
tid = (long)threadid;
Node* cur_node;
ThreadEnv* thisThread;
thisThread = threadEnv + tid;
#if 0
if (tid == 0)
global_relabel(tid);
#endif
pthread_barrier_wait(&start_barrier);
while (!flow_done()) {
cur_node = thisThread->Q[0];
while (cur_node != NoNode) {
#ifdef GR
if (op_times > gr_threshold) {
op_times = 0;
if (pthread_mutex_trylock(&gr_mutex) == 0) {
global_relabel(tid);
pthread_mutex_unlock(&gr_mutex);
}
}
#endif
while (cur_node->excess > 0) {
#ifdef DEBUG
fprintf(stderr,
"%d h=%d, e=%ld\n",
cur_node - g_node,
cur_node->height,
cur_node->excess);
fflush(stderr);
#endif
min_nbr_height = UINT_MAX;
for (nbr_edge = cur_node->adj_list; nbr_edge < (cur_node + 1)->adj_list;
nbr_edge++) {
if (nbr_edge->capacity > 0 &&
(nbr_edge->endpoint)->height < min_nbr_height) {
min_nbr_height = (nbr_edge->endpoint)->height;
min_height_edge = nbr_edge;
}
}
#ifdef DEBUG
fprintf(stderr, "work on %d\n", cur_node - g_node);
fflush(stderr);
#endif
if (cur_node->height > min_nbr_height) {
local_e = cur_node->excess;
local_c = min_height_edge->capacity;
d = MIN(local_e, local_c);
if (min_height_edge->endpoint->wave == cur_node->wave &&
cur_node->height > min_height_edge->endpoint->height) {
node_push_times++;
op_times++;
atomic_add(d, &(min_height_edge->mateedge->capacity));
atomic_sub(d, &(min_height_edge->capacity));
atomic_add(d, &((min_height_edge->endpoint)->excess));
atomic_sub(d, &(cur_node->excess));
#if defined(PUSH) || defined(DEBUG)
fprintf(stderr,
"[%ld] %ld(%ld) -> %ld -> %ld(%ld) \n",
tid,
cur_node - g_node,
cur_node->excess,
d,
min_height_edge->endpoint - g_node,
(min_height_edge->endpoint)->excess);
fflush(stderr);
#endif
// add min_nbr to local queue
isInQ = cmpxchg(&(min_height_edge->endpoint->inQ), 0, tid + 1);
if (isInQ == 0)
enQ(thisThread, min_height_edge->endpoint);
}
} else {
// if we cannot push to any nodes, then we must be able to lift
node_lift_times++;
op_times++;
pthread_mutex_lock(&(node_mutex[cur_node - g_node]));
if (cur_node->height < min_nbr_height + 1)
cur_node->height = min_nbr_height + 1;
pthread_mutex_unlock(&(node_mutex[cur_node - g_node]));
#if defined(LIFT) || defined(DEBUG)
fprintf(stderr,
"%ld ^ %d, ref %ld(%d)\n",
cur_node - g_node,
cur_node->height,
min_height_edge->endpoint - g_node,
min_height_edge->endpoint->height);
fflush(stderr);
#endif
}
} // while( g_node[i].excess > 0 )
set0(&(cur_node->inQ));
if (cur_node->excess > 0) {
isInQ = cmpxchg(&(cur_node->inQ), 0, tid + 1);
if (isInQ == 0) {
reenQ(thisThread, cur_node);
} else {
deQ(thisThread);
}
} else {
deQ(thisThread);
}
#ifdef HELP
if (thisThread->request < MAX_THRD)
send_work(tid);
#endif
cur_node = thisThread->Q[thisThread->head];
} // while (i != -1)
#ifdef HELP
// Q is empty, find something to do;
request_work(tid);
#else
break;
#endif
} // while(!flow_done())
atomic_add(node_push_times, &(totalPushes));
atomic_add(node_lift_times, &(totalLifts));
} // scan_node
double maxflow (GRAPH *gr, GRAPHNODE *s_ptr, GRAPHNODE *t_ptr)
{
/* Determines maximum flow and minimum cut between nodes
s (= *s_ptr) and t (= *t_ptr) in an undirected graph
References:
----------
A. Goldberg/ E. Tarjan: "A New Approach to the
Maximum Flow Problem", in Proc. 18th ACM Symp.
on Theory of Computing, 1986.
*/
GRAPHNODE *aptr, *nptr, *q_front, *q_rear;
GRAPHEDGE *eptr;
long n, m, m0, level, i, n_discharge;
double incre;
long dmin;
double cap;
/* node ids range from 1 to n, node array indices
range from 0 to n-1 */
n = gr->nnodes;
for ( nptr = &(gr->nodes[n-1L]); nptr >= gr->nodes; nptr-- )
{
nptr->scan_ptr = nptr->first_edge;
while( nptr->scan_ptr != NULL && nptr->scan_ptr->cap <= EPS )
nptr->scan_ptr = nptr->scan_ptr->next;
if ( nptr->scan_ptr == NULL )
{
fprintf (stderr, "isolated node in input graph\n");
return (FALSE);
}
nptr->excess = 0.0L;
nptr->stack_link = NULL;
nptr->alive = TRUE;
nptr->unmarked = TRUE;
}
m = gr->nedgesnonzero;
m0 = gr->nedges;
for ( eptr = &(gr->edges[m-1L]); eptr >= gr->edges; eptr-- )
eptr->rcap = eptr->cap;
for ( eptr = &(gr->edges[m0+m-1L]); eptr >= &(gr->edges[m0]); eptr-- )
eptr->rcap = eptr->cap;
for ( i = n; i >= 0L; i-- )
{
number[i] = 0L;
active[i] = NULL;
}
t_ptr->dist = 0L;
/* breadth first search to get exact distances
from sink and for test of graph connectivity */
t_ptr->unmarked = FALSE;
q_front = t_ptr;
q_rear = q_front;
bfs_next:
level = q_rear->dist + 1L;
eptr = q_rear->first_edge;
while ( eptr != NULL )
{
assert(eptr->back->cap == eptr->back->rcap);
if ( eptr->adjac->unmarked && eptr->back->rcap > EPS )
{
nptr = eptr->adjac;
nptr->unmarked = FALSE;
nptr->dist = level;
++number[level];
q_front->bfs_link = nptr;
q_front = nptr;
}
eptr = eptr->next;
}
if ( q_rear == q_front )
goto bfs_ready;
q_rear = q_rear->bfs_link;
goto bfs_next;
bfs_ready:
if ( co_check )
{
co_check = FALSE;
for ( nptr = &(gr->nodes[n-1]); nptr >= gr->nodes; --nptr )
{
if ( nptr->unmarked )
return (-1.0L);
}
}
s_ptr->dist = n; /* number[0] and number[n] not required */
t_ptr->dist = 0L;
t_ptr->excess = 1.0L; /* to be subtracted again */
/* initial preflow push from source node */
max_dist = 0L; /* = max_dist of active nodes */
eptr = s_ptr->first_edge;
while ( eptr != NULL )
{
if( eptr->cap > EPS )
{
nptr = eptr->adjac;
cap = eptr->rcap;
nptr->excess += cap;
s_ptr->excess -= cap;
eptr->back->rcap += cap;
eptr->rcap = 0.0L;
if ( nptr != t_ptr && nptr->excess <= cap + EPS )
{
/* push node nptr onto stack for nptr->dist,
but only once in case of double edges */
nptr->stack_link = active[nptr->dist];
active[nptr->dist] = nptr;
if ( nptr->dist > max_dist )
max_dist = nptr->dist;
}
}
eptr = eptr->next;
}
s_ptr->alive = FALSE;
bound = n;
n_discharge = 0L;
/* main loop */
do
{
/* get maximum distance active node */
aptr = active[max_dist];
while ( aptr != NULL )
{
active[max_dist] = aptr->stack_link;
eptr = aptr->scan_ptr;
assert(eptr != NULL);
assert(eptr->back != NULL);
assert(eptr->cap > EPS);
edge_scan: /* for current active node */
assert(eptr != NULL);
assert(eptr->back != NULL);
assert(eptr->cap > EPS);
nptr = eptr->adjac;
assert(nptr != NULL);
if ( nptr->dist == aptr->dist - 1L && eptr->rcap > EPS )
{
incre = aptr->excess;
if ( incre <= eptr->rcap )
{
/* perform a non saturating push */
eptr->rcap -= incre;
eptr->back->rcap += incre;
aptr->excess = 0.0L;
nptr->excess += incre;
if ( nptr->excess <= incre + EPS )
{
/* push nptr onto active stack */
nptr->stack_link = active[nptr->dist];
active[nptr->dist] = nptr;
}
assert(eptr->cap > EPS);
aptr->scan_ptr = eptr;
goto node_ready;
}
else
{
/* perform a saturating push */
incre = eptr->rcap;
eptr->back->rcap += incre;
aptr->excess -= incre;
nptr->excess += incre;
eptr->rcap = 0.0L;
if ( nptr->excess <= incre + EPS )
{
/* push nptr onto active stack */
nptr->stack_link = active[nptr->dist];
active[nptr->dist] = nptr;
}
if ( aptr->excess <= EPS )
{
assert(eptr->cap > EPS);
aptr->scan_ptr = eptr;
goto node_ready;
}
}
}
/* go to the next non-zero edge */
do
{
eptr = eptr->next;
}
while( eptr != NULL && eptr->cap <= EPS );
if ( eptr == NULL )
{
/* all incident arcs scanned, but node still
has positive excess, check if for all nptr
nptr->dist != aptr->dist */
if ( number[aptr->dist] == 1L )
{
/* put all nodes v with dist[v] >= dist[a]
into the set of "dead" nodes since they
are disconnected from the sink */
for ( nptr = &(gr->nodes[n-1L]); nptr >= gr->nodes; nptr-- )
{
if ( nptr->alive && nptr->dist > aptr->dist )
{
--number[nptr->dist];
active[nptr->dist] = NULL;
nptr->alive = FALSE;
nptr->dist = n;
--bound;
}
}
--number[aptr->dist];
active[aptr->dist] = NULL;
aptr->alive = FALSE;
aptr->dist = n;
--bound;
goto node_ready;
}
else
{
/* determine new label value */
dmin = n;
aptr->scan_ptr = NULL;
eptr = aptr->first_edge;
while ( eptr != NULL )
{
assert(eptr->rcap <= EPS || eptr->cap > EPS);
if ( eptr->adjac->dist < dmin && eptr->rcap > EPS )
{
assert(eptr->cap > EPS);
dmin = eptr->adjac->dist;
if ( aptr->scan_ptr == NULL )
aptr->scan_ptr = eptr;
}
eptr = eptr->next;
}
if ( ++dmin < bound )
{
/* ordinary relabel operation */
--number[aptr->dist];
aptr->dist = dmin;
++number[dmin];
max_dist = dmin;
eptr = aptr->scan_ptr;
assert(eptr != NULL);
assert(eptr->cap > EPS);
goto edge_scan;
}
else
{
aptr->alive = FALSE;
--number[aptr->dist];
aptr->dist = n;
--bound;
goto node_ready;
}
}
}
else
goto edge_scan;
node_ready:
++n_discharge;
if ( n_discharge == n )
{
n_discharge = 0L;
global_relabel (gr, t_ptr);
}
aptr = active[max_dist];
} /* aptr != NULL */
--max_dist;
}
while ( max_dist > 0L );
return (t_ptr->excess - 1.0L);
}