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/* Copyright 2016-present Facebook, Inc.
* Licensed under the Apache License, Version 2.0 */
#include "PubSub.h"
#include <algorithm>
#include <iterator>
namespace watchman {
Publisher::Subscriber::Subscriber(
std::shared_ptr<Publisher> pub,
Notifier notify,
const w_string& info)
: serial_(0),
publisher_(std::move(pub)),
notify_(notify),
info_(std::move(info)) {}
Publisher::Subscriber::~Subscriber() {
auto wlock = publisher_->state_.wlock();
auto it = wlock->subscribers.begin();
while (it != wlock->subscribers.end()) {
auto sub = it->lock();
// Prune vacated weak_ptr's or those that point to us
if (!sub || sub.get() == this) {
it = wlock->subscribers.erase(it);
} else {
++it;
}
}
// Take this opportunity to reap anything that is no longer
// referenced now that we've removed some subscriber(s)
wlock->collectGarbage();
}
void Publisher::Subscriber::getPending(
std::vector<std::shared_ptr<const Item>>& pending) {
{
auto rlock = publisher_->state_.rlock();
auto& items = rlock->items;
if (items.empty()) {
return;
}
// First we walk back to find the end of the range that
// we have seen previously.
int firstIndex;
for (firstIndex = int(items.size()) - 1; firstIndex >= 0; --firstIndex) {
if (items[firstIndex]->serial <= serial_) {
break;
}
}
// We found the item before the one we really want, so
// increment the index; we'll copy the remaining items.
++firstIndex;
bool updated = false;
while (firstIndex < int(items.size())) {
pending.push_back(items[firstIndex]);
++firstIndex;
updated = true;
}
if (updated) {
serial_ = pending.back()->serial;
}
return;
}
}
void getPending(
std::vector<std::shared_ptr<const Publisher::Item>>& items,
const std::shared_ptr<Publisher::Subscriber>& sub1,
const std::shared_ptr<Publisher::Subscriber>& sub2) {
if (sub1) {
sub1->getPending(items);
}
if (sub2) {
sub2->getPending(items);
}
}
std::shared_ptr<Publisher::Subscriber> Publisher::subscribe(
Notifier notify,
const w_string& info) {
auto sub =
std::make_shared<Publisher::Subscriber>(shared_from_this(), notify, info);
state_.wlock()->subscribers.emplace_back(sub);
return sub;
}
bool Publisher::hasSubscribers() const {
return !state_.rlock()->subscribers.empty();
}
void Publisher::state::collectGarbage() {
if (items.empty()) {
return;
}
uint64_t minSerial = std::numeric_limits<uint64_t>::max();
for (auto& it : subscribers) {
auto sub = it.lock();
if (sub) {
minSerial = std::min(minSerial, sub->getSerial());
}
}
while (!items.empty() && items.front()->serial < minSerial) {
items.pop_front();
}
}
bool Publisher::enqueue(json_ref&& payload) {
std::vector<std::shared_ptr<Subscriber>> subscribers;
{
auto wlock = state_.wlock();
// We need to collect live references for the notify portion,
// but since we're holding the wlock, take this opportunity to
// detect and prune dead subscribers and clean up some garbage.
auto it = wlock->subscribers.begin();
while (it != wlock->subscribers.end()) {
auto sub = it->lock();
// Prune vacated weak_ptr's
if (!sub) {
it = wlock->subscribers.erase(it);
} else {
++it;
// Remember that live reference so that we can notify
// outside of the lock below.
subscribers.emplace_back(std::move(sub));
}
}
wlock->collectGarbage();
if (subscribers.empty()) {
return false;
}
auto item = std::make_shared<Item>();
item->payload = std::move(payload);
item->serial = wlock->nextSerial++;
wlock->items.emplace_back(std::move(item));
}
// and notify them outside of the lock
for (auto& sub : subscribers) {
auto& n = sub->getNotify();
if (n) {
n();
}
}
return true;
}
json_ref Publisher::getDebugInfo() const {
auto ret = json_object();
auto rlock = state_.rlock();
ret.set("next_serial", json_integer(rlock->nextSerial));
auto subscribers = json_array();
auto& subscribers_arr = subscribers.array();
for (auto& sub_ref : rlock->subscribers) {
auto sub = sub_ref.lock();
if (sub) {
auto sub_json = json_object({{"serial", json_integer(sub->getSerial())},
{"info", w_string_to_json(sub->getInfo())}});
subscribers_arr.emplace_back(sub_json);
} else {
// This is a subscriber that is now dead. It will be cleaned up the next
// time enqueue is called.
}
}
ret.set("subscribers", std::move(subscribers));
auto items = json_array();
auto& items_arr = items.array();
for (auto& item : rlock->items) {
auto item_json = json_object(
{{"serial", json_integer(item->serial)}, {"payload", item->payload}});
items_arr.emplace_back(item_json);
}
ret.set("items", std::move(items));
return ret;
}
}
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