askrene: implement 10-second deadline.

We have another report of looping.  This maxparts code is being completely
rewritten, but it's good to have a catchall for any other cases which might
emerge.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Author: rustyrussell

plugins/askrene/askrene.c

@@ -614,13 +614,14 @@ static struct command_result *do_getroutes(struct command *cmd,
 	/* Compute the routes. At this point we might select between multiple
 	 * algorithms. Right now there is only one algorithm available. */
 	struct timemono time_start = time_mono();
+	struct timemono deadline = timemono_add(time_start, time_from_sec(10));
 	if (info->dev_algo == ALGO_SINGLE_PATH) {
-		err = single_path_routes(rq, rq, srcnode, dstnode, info->amount,
+		err = single_path_routes(rq, rq, deadline, srcnode, dstnode, info->amount,
 					 info->maxfee, info->finalcltv,
 					 info->maxdelay, &flows, &probability);
 	} else {
 		assert(info->dev_algo == ALGO_DEFAULT);
-		err = default_routes(rq, rq, srcnode, dstnode, info->amount,
+		err = default_routes(rq, rq, deadline, srcnode, dstnode, info->amount,
 				     info->maxfee, info->finalcltv,
 				     info->maxdelay, &flows, &probability);
 	}

plugins/askrene/mcf.c

@@ -1346,6 +1346,7 @@ static bool check_htlc_max_limits(struct route_query *rq, struct flow **flows)
  */
 static const char *
 linear_routes(const tal_t *ctx, struct route_query *rq,
+	      struct timemono deadline,
 	      const struct gossmap_node *srcnode,
 	      const struct gossmap_node *dstnode, struct amount_msat amount,
 	      struct amount_msat maxfee, u32 finalcltv, u32 maxdelay,
@@ -1379,6 +1380,13 @@ linear_routes(const tal_t *ctx, struct route_query *rq,
 		size_t num_parts, parts_slots, excess_parts;
 		u32 bottleneck_idx;
 
+		if (timemono_after(time_mono(), deadline)) {
+			error_message = rq_log(ctx, rq, LOG_BROKEN,
+					       "%s: timed out after deadline",
+					       __func__);
+			goto fail;
+		}
+
                 /* FIXME: This algorithm to limit the number of parts is dumb
                  * for two reasons:
                  *      1. it does not take into account that several loop
@@ -1641,25 +1649,27 @@ linear_routes(const tal_t *ctx, struct route_query *rq,
 }
 
 const char *default_routes(const tal_t *ctx, struct route_query *rq,
+			   struct timemono deadline,
 			   const struct gossmap_node *srcnode,
 			   const struct gossmap_node *dstnode,
 			   struct amount_msat amount, struct amount_msat maxfee,
 			   u32 finalcltv, u32 maxdelay, struct flow ***flows,
 			   double *probability)
 {
-	return linear_routes(ctx, rq, srcnode, dstnode, amount, maxfee,
+	return linear_routes(ctx, rq, deadline, srcnode, dstnode, amount, maxfee,
 			     finalcltv, maxdelay, flows, probability, minflow);
 }
 
 const char *single_path_routes(const tal_t *ctx, struct route_query *rq,
+			       struct timemono deadline,
 			       const struct gossmap_node *srcnode,
 			       const struct gossmap_node *dstnode,
 			       struct amount_msat amount,
 			       struct amount_msat maxfee, u32 finalcltv,
 			       u32 maxdelay, struct flow ***flows,
 			       double *probability)
 {
-	return linear_routes(ctx, rq, srcnode, dstnode, amount, maxfee,
+	return linear_routes(ctx, rq, deadline, srcnode, dstnode, amount, maxfee,
 			     finalcltv, maxdelay, flows, probability,
 			     single_path_flow);
 }

plugins/askrene/mcf.h

@@ -64,6 +64,7 @@ struct amount_msat linear_flow_cost(const struct flow *flow,
 /* A wrapper to the min. cost flow solver that actually takes into consideration
  * the extra msats per channel needed to pay for fees. */
 const char *default_routes(const tal_t *ctx, struct route_query *rq,
+			   struct timemono deadline,
 			   const struct gossmap_node *srcnode,
 			   const struct gossmap_node *dstnode,
 			   struct amount_msat amount,
@@ -73,6 +74,7 @@ const char *default_routes(const tal_t *ctx, struct route_query *rq,
 
 /* A wrapper to the single-path constrained solver. */
 const char *single_path_routes(const tal_t *ctx, struct route_query *rq,
+			       struct timemono deadline,
 			       const struct gossmap_node *srcnode,
 			       const struct gossmap_node *dstnode,
 			       struct amount_msat amount,