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common/random_select: central place for reservoir sampling.

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Turns out we can make quite a simple API out of it.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell
2020-08-11 14:35:56 +09:30
parent 12d0d5c185
commit 496c0dd1e6
11 changed files with 76 additions and 59 deletions
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1
plugins/Makefile
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@@ -70,6 +70,7 @@ PLUGIN_COMMON_OBJS := \
common/node_id.o \
common/param.o \
common/pseudorand.o \
common/random_select.o \
common/setup.o \
common/type_to_string.o \
common/utils.o \

36
plugins/libplugin-pay.c
View File

@@ -3,6 +3,7 @@
#include <ccan/tal/str/str.h>
#include <common/json_stream.h>
#include <common/pseudorand.h>
#include <common/random_select.h>
#include <common/type_to_string.h>
#include <plugins/libplugin-pay.h>
@@ -2421,12 +2422,11 @@ static struct command_result *shadow_route_listchannels(struct command *cmd,
const jsmntok_t *result,
struct payment *p)
{
/* Use reservoir sampling across the capable channels. */
struct shadow_route_data *d = payment_mod_shadowroute_get_data(p);
struct payment_constraints *cons = &d->constraints;
struct route_info *best = NULL;
double total_weight = 0.0;
size_t i;
u64 sample = 0;
struct amount_msat best_fee;
const jsmntok_t *sattok, *delaytok, *basefeetok, *propfeetok, *desttok,
*channelstok, *chan, *scidtok;
@@ -2438,7 +2438,6 @@ static struct command_result *shadow_route_listchannels(struct command *cmd,
channelstok = json_get_member(buf, result, "channels");
json_for_each_arr(i, chan, channelstok) {
u64 v = pseudorand(UINT64_MAX);
struct route_info curr;
struct amount_sat capacity;
struct amount_msat fee;
@@ -2465,28 +2464,27 @@ static struct command_result *shadow_route_listchannels(struct command *cmd,
json_to_sat(buf, sattok, &capacity);
json_to_node_id(buf, desttok, &curr.pubkey);
if (!best || v > sample) {
/* If the capacity is insufficient to pass the amount
* it's not a plausible extension. */
if (amount_msat_greater_sat(p->amount, capacity))
continue;
/* If the capacity is insufficient to pass the amount
* it's not a plausible extension. */
if (amount_msat_greater_sat(p->amount, capacity))
continue;
if (curr.cltv_expiry_delta > cons->cltv_budget)
continue;
if (curr.cltv_expiry_delta > cons->cltv_budget)
continue;
if (!amount_msat_fee(
&fee, p->amount, curr.fee_base_msat,
curr.fee_proportional_millionths)) {
/* Fee computation failed... */
continue;
}
if (!amount_msat_fee(
&fee, p->amount, curr.fee_base_msat,
curr.fee_proportional_millionths)) {
/* Fee computation failed... */
continue;
}
if (amount_msat_greater_eq(fee, cons->fee_budget))
continue;
if (amount_msat_greater_eq(fee, cons->fee_budget))
continue;
if (random_select(1.0, &total_weight)) {
best = tal_dup(tmpctx, struct route_info, &curr);
best_fee = fee;
sample = v;
}
}