one/include/ReplicaRequest.h

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/* Copyright 2002-2023, OpenNebula Project, OpenNebula Systems                */
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/* -------------------------------------------------------------------------- */

#ifndef REPLICA_REQUEST_H_
#define REPLICA_REQUEST_H_

#include "SyncRequest.h"

/**
 * This class represents a log entry replication request. The replication request
 * is synchronous: once it has been replicated in a majority of followers the
 * client is notified (SqlDB::exec_wr() call) and DB updated.
 */
class ReplicaRequest : public SyncRequest
{
public:
    ReplicaRequest(uint64_t i):_index(i), _to_commit(-1), _replicas(1){};

    ~ReplicaRequest(){};

    /**
     *  This function updates the number of replicas of the record and decrement
     *  the number of servers left to reach majority consensus. If it reaches 0,
     *  the client is notified
     *      @return number of replicas for this log
     */
    int add_replica()
    {
        int __replicas;

        _replicas++;

        if ( _to_commit > 0 )
        {
            _to_commit--;
        }

        __replicas = _replicas;

        if ( _to_commit == 0 )
        {
            result  = true;
            timeout = false;

            notify();
        }

        return __replicas;
    }

    /* ---------------------------------------------------------------------- */
    /* Class access methods                                                   */
    /* ---------------------------------------------------------------------- */
    uint64_t index()
    {
        return _index;
    }

    int replicas()
    {
        return _replicas;
    }

    int to_commit()
    {
        return _to_commit;
    }

    void to_commit(int c)
    {
        _to_commit = c;
    }

private:
    /**
     *  Index for this log entry
     */
    uint64_t _index;

    /**
     *  Remaining number of servers that need to replicate this record to commit
     *  it. Initialized to ( Number_Servers - 1 ) / 2
     */
    int _to_commit;

    /**
     *  Total number of replicas for this entry
     */
    int _replicas;
};

/**
 * This class represents a map of replication requests. It syncs access between
 * RaftManager and DB writer threads. A DB writer allocates and set the
 * request and then it waits on it for completion.
 */
class ReplicaRequestMap
{
public:
    ReplicaRequestMap() = default;

    virtual ~ReplicaRequestMap() = default;

    /**
     *  Increments the number of replicas of this request. If it can be
     *  committed the request is removed from the map
     *    @param rindex of the request
     *
     *    @return the number of replicas to commit, if 0 it can be committed
     */
    int add_replica(uint64_t rindex)
    {
        int to_commit = -1;

        std::lock_guard<std::mutex> lock(_mutex);

        auto it = requests.find(rindex);

        if ( it != requests.end() && it->second )
        {
            it->second->add_replica();

            to_commit = it->second->to_commit();

            if ( to_commit == 0 )
            {
                requests.erase(it);
            }
        }

        return to_commit;
    }

    /**
     *  Allocated an empty replica request. It marks a writer thread will wait
     *  on this request.
     *    @param rindex of the request
     */
    void allocate(uint64_t rindex)
    {
        std::lock_guard<std::mutex> lock(_mutex);

        requests.insert(std::make_pair(rindex, (ReplicaRequest*) 0));
    }

    /**
     * Set the replication request associated to this index. If there is no
     * previous request associated to the index it is created.
     *   @param rindex of the request
     *   @param rr replica request pointer
     */
    void set(uint64_t rindex, ReplicaRequest * rr)
    {
        std::lock_guard<std::mutex> lock(_mutex);

        requests[rindex] = rr;
    }

    /**
     *  Remove a replication request associated to this index
     *   @param rindex of the request
     */
    void remove(uint64_t rindex)
    {
        std::lock_guard<std::mutex> lock(_mutex);

        requests.erase(rindex);
    }

    /**
     *  Notify all writers and clear the replica map
     */
    void clear()
    {
        std::lock_guard<std::mutex> lock(_mutex);

        for ( auto it = requests.begin() ; it != requests.end() ; ++it )
        {
            if ( it->second == 0 )
            {
                continue;
            }

            it->second->result  = false;
            it->second->timeout = false;
            it->second->message = "oned is now follower";

            it->second->notify();
        }

        requests.clear();
    }

    /**
     *  @return true if a replica request is set for this index
     */
    bool is_replicable(uint64_t rindex)
    {
        std::lock_guard<std::mutex> lock(_mutex);

        auto it = requests.find(rindex);

        return (it == requests.end()) || (it->second != nullptr);
    }

private:

    std::mutex _mutex;

    /**
     * Clients waiting for a log replication
     */
    std::map<uint64_t, ReplicaRequest *> requests;
};

#endif /*REPLICA_REQUEST_H_*/