db-lab1/bserv/session.cpp

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#include "pch.h"
#include "bserv/session.hpp"
namespace bserv {
bool memory_session_manager::get_or_create(
std::string& key,
std::shared_ptr<session_type>& session_ptr) {
std::lock_guard<std::mutex> lg{ lock_ };
time_point now = std::chrono::steady_clock::now();
// removes the expired sessions
while (!queue_.empty() && queue_.begin()->first < now) {
std::size_t another_key = queue_.begin()->second;
sessions_.erase(another_key);
expiry_.erase(another_key);
str_to_int_.erase(int_to_str_[another_key]);
int_to_str_.erase(another_key);
queue_.erase(queue_.begin());
}
bool created = false;
std::size_t int_key;
if (key.empty() || str_to_int_.count(key) == 0) {
do {
key = utils::generate_random_string(32);
} while (str_to_int_.count(key) != 0);
do {
int_key = dist_(rng_);
} while (int_to_str_.count(int_key) != 0);
str_to_int_[key] = int_key;
int_to_str_[int_key] = key;
sessions_[int_key] = std::make_shared<session_type>();
created = true;
}
else {
int_key = str_to_int_[key];
queue_.erase(
queue_.lower_bound(
std::make_pair(expiry_[int_key], int_key)));
}
// the expiry is set to be 20 minutes from now.
// if the session is re-visited within 20 minutes,
// the expiry will be extended.
expiry_[int_key] = now + std::chrono::minutes(20);
// pushes expiry-key tuple (pair) to the queue
queue_.emplace(expiry_[int_key], int_key);
session_ptr = sessions_[int_key];
return created;
}
} // bserv