/**
 * Replica Consistent Read Manager
 */

#include "replica_read_manager.h"

#include "mysqld.h"

uint64_t opt_replica_read_timeout = 0;

ReplicaReadManager replica_read_manager;

void ReplicaReadManager::update_lsn(uint64_t new_lsn) {
    std::unique_lock<std::mutex> lock(m_mutex);
    // Make sure the applied index must be monotonically increasing
    if (new_lsn <= m_applied_lsn.load(std::memory_order_acquire)) {
        return;
    }

    while (!m_wait_queue.empty() && m_wait_queue.top()->lsn <= new_lsn) {
        m_wait_queue.top()->cv.notify_one();
        m_wait_queue.pop();
    }

    m_applied_lsn.store(new_lsn, std::memory_order_release);
}

bool ReplicaReadManager::wait_for_lsn(uint64_t read_lsn) {
    // fast lock-free check
    if (read_lsn <= m_applied_lsn.load(std::memory_order_acquire)) {
        return true;
    }

    std::unique_lock<std::mutex> lock(m_mutex);
    if (read_lsn <= m_applied_lsn.load(std::memory_order_acquire)) {
        return true;
    }

    ReadLsnCond cond(read_lsn);
    m_wait_queue.push(&cond);
    auto status = cond.cv.wait_for(lock, std::chrono::milliseconds(opt_replica_read_timeout));
    if (status == std::cv_status::timeout) {
        m_wait_queue.erase(&cond);
        if (read_lsn <= m_applied_lsn.load(std::memory_order_acquire)) {
            return true;
        }
        return false;
    } else {
        return true;
    }
}