mongoDB 和 nodeJs 无法正确处理并发请求

Question

我正在开发基于 socket.io room 的项目。我将 socket 与 nodejs 一起使用并在 mongoDB 中管理房间数据。

这是我的代码，只有两个玩家可以加入一个房间，然后我将 IsGameOn 标志设置为 false 为 true。
当我一一向服务器发送请求时，此代码工作正常。
当一次有多个请求时会出现问题。问题是超过 2 个玩家加入房间（房间玩家的数据存储在一个玩家数组中）。

我还上传了数据库的图像。因此，您可以看到数据库中实际发生的情况。

const joinRoom = async (sData, callback) => {

if(sData.iPlayerId && sData.eRoomCount)
{
    try {

        let body = _.pick(sData, ['eRoomCount', 'iPlayerId']);

        console.log(body);

        await roomsModel.aggregate([
            {
                $match: {
                    eRoomCount: body.eRoomCount,
                    IsGameOn: { $eq: false }
                }
            },
            { $unwind: "$aPlayers" },
            {
                $group: {
                    _id: "$_id",
                    eRoomCount: { $first: "$eRoomCount" },
                    aPlayers: { $push: "$aPlayers" },
                    size: { $sum: 1 }
                }
            },
            {
                $match: {
                    size: { '$lt': body.eRoomCount }
                }
            },
            { $sort: { size: -1 } }
        ]).exec((error, data) => {
            if (data.length < 1) {

                let params = {
                    eRoomCount: body.eRoomCount,
                    aPlayers: [{
                        iPlayerId: body.iPlayerId
                    }]
                }
                let newRoom = new roomsModel(params);
                console.log(JSON.stringify(newRoom));
                newRoom.save().then((room) => {
                    console.log("succ", room);
                    callback(null,room);
                }).catch((e) => {
                    callback(e,null);
                });
            } else {
                roomsModel.findOne({ _id: data[0]._id }, (error, room) => {

                    if (error) {
                        callback(error,null);
                    }

                    if (!room) {
                        console.log("No room found");
                        callback("No room found",null);
                    }

                    room.aPlayers.push({ iPlayerId: body.iPlayerId });
                    if (room.aPlayers.length === room.eRoomCount) {
                        room.IsGameOn = true;
                    }

                    room.save().then((room) => {
                        callback(null,room);
                    }).catch((e) => {
                        callback(e,null);
                    });

                })
            }
        });

    } catch (e) {
        console.log(`Error :: ${e}`);
        let err = `Error :: ${e}`;
        callback(e,null);
    }
    }
}

当请求一个接一个时会发生这种情况。

当一次有多个请求时会发生这种情况。

Answer 1

正确的方法是使用猫鼬的findOneAndUpdate 而不是findOne。操作findOneAndUpdate 是原子的。如果你做正确的查询，你可以让你的代码线程安全。

// This makes sure, that only rooms with one or no player gets selected.
query = {
    // Like before
    _id: data[0]._id,
    // This is a bit inelegant and can be improved (but would work fast)
    $or: {
        { aPlayers: { $size: 0 } },
        { aPlayers: { $size: 1 } }
    }
}

// $addToSet only adds a value to a set if it not present.
// This prevents a user playing vs. him/herself
update = { $addToSet: { aPlayers: { iPlayerId: body.iPlayerId } } }

// This returns the updated document, not the old one
options = { new: true }

// Execute the query
// You can pass in a callback function
db.rooms.findOneAndUpdate(query, update, options, callback)

Answer 2

对于这个问题，您可以使用信号量模块，在您的情况下，节点服务器在单线程环境中访问并发请求，但操作系统执行多任务工作。信号量模块将帮助您摆脱这个地狱。

• npm i semaphore            （安装模块）
• const sem = require('信号量')(1); （此处要求并指定并发请求限制                    其1）
• sem.take(函数()); （将您的函数包装在其中）

• sem.leave(); （处理完成后调用它，然后下一个请求                   将访问该函数）
  

  const joinRoom = (sData, callback) => {
  
    sem.take(function () {
      if (sData.iPlayerId && sData.eRoomCount) {
  
        try {
  
          let body = _.pick(sData, ['eRoomCount', 'iPlayerId']);
          roomsModel.aggregate([
            {
              $match: {
                eRoomCount: body.eRoomCount,
                IsGameOn: { $eq: false }
              }
            },
            { $unwind: "$aPlayers" },
            {
              $group: {
                _id: "$_id",
                eRoomCount: { $first: "$eRoomCount" },
                aPlayers: { $push: "$aPlayers" },
                size: { $sum: 1 }
              }
            },
            {
              $match: {
                    size: { '$lt': body.eRoomCount }
                  }
                },
                { $sort: { size: -1 } }
              ]).exec((error, data) => {
                if (data.length < 1) {
  
                  let params = {
                    eRoomCount: body.eRoomCount,
                    aPlayers: [{
                      iPlayerId: body.iPlayerId
                    }]
                  }
                  let newRoom = new roomsModel(params);
                  console.log(JSON.stringify(newRoom));
                  newRoom.save().then((room) => {
                    console.log("succ", room);
                    sem.leave();
                    callback(null, room);
                  }).catch((e) => {
                    sem.leave();
                    callback(e, null);
                  });
                } else {
                  roomsModel.findOne({ _id: data[0]._id }, (error, room) => {
                    if (error) {
                      sem.leave();
                      callback(error, null);
                    }
                    if (!room) {
                      console.log("No room found");
                      sem.leave();
                      callback("No room found", null);
                    }
                    room.aPlayers.push({ iPlayerId: body.iPlayerId });
                    if (room.aPlayers.length === room.eRoomCount) {
                      room.IsGameOn = true;
                    }
                    room.save().then((room) => {
                      sem.leave();
                      callback(null, room);
                    }).catch((e) => {
                      sem.leave();
                      callback(e, null);
                    });
                  });
                }
              });
            } catch (e) {
              console.log(`Error :: ${e}`);
              let err = `Error :: ${e}`;
              callback(e, null);
            }
          }
        });
      }