从 Redis 检索多个键时死锁

Question

我试图将此查询的结果并行获取到 redis（使用 stackexchange C# 客户端），但不知何故我运行陷入僵局并且不确定在哪里

获取数据的方法：

public LiveData Get(string sessionId)
{
    return GetAsync(sessionId).Result;
}

private async Task<LiveData> GetAsync(string sessionId)
{
    var basketTask = GetBasketAsync(sessionId);
    var historyTask = GetHistoryAsync(sessionId);
    var capturedDataTask = GetCapturedDataAsync(sessionId);

    var basket = await basketTask;
    var history = await historyTask;
    var capturedData = await capturedDataTask;

    return new LiveData
    {
        Basket = basket.IsNullOrEmpty
            ? new List<Product>()
            : JsonConvert.DeserializeObject<List<Product>>(basket),
        History = history.Select(cachedProduct
            => JsonConvert.DeserializeObject<Product>(cachedProduct.Value.ToString())).ToList(),
        CapturedData = capturedData.ToDictionary<HashEntry, string, object>(
            hash => hash.Name, hash => JsonConvert.DeserializeObject(hash.Value))
    };
}

而从redis中获取缓存数据的方法是：

private async Task<RedisValue> GetBasketAsync(string key)
{
    key = $"{key}{BasketSuffix}";
    var redisDb = RedisConnection.Connection.GetDatabase();
    redisDb.KeyExpireAsync(key, _expire);

    return await redisDb.StringGetAsync(key);
}

private async Task<HashEntry[]> GetHistoryAsync(string key)
{
    key = $"{key}{HistorySuffix}";
    var redisDb = RedisConnection.Connection.GetDatabase();
    redisDb.KeyExpireAsync(key, _expire);

    return await redisDb.HashGetAllAsync(key);
}

private async Task<HashEntry[]> GetCapturedDataAsync(string key)
{
    key = $"{key}{CapturedDataSuffix}";
    var redisDb = RedisConnection.Connection.GetDatabase();
    redisDb.KeyExpireAsync(key, _expire);

    return await redisDb.HashGetAllAsync(key);
}

我认为这样调用 KeyExpireAsync 很好，只是因为它可以触发并忘记但不确定是否相关（我什至尝试删除它但它仍然被阻止）

Answer 1

死锁的根源是这个片段：

public LiveData Get(string sessionId)
{
    return GetAsync(sessionId).Result;
}

相反，以正确的方式调用它 "async all the way":

public async Task<LiveData> Get(string sessionId)
{
    return await GetAsync(sessionId);
}

调用 .Result 会导致死锁，使用 .Wait() API 也会导致死锁。此外，从外观上看 -- .KeyExpireAsync 需要等待。

async Task<RedisValue> GetBasketAsync(string key)
{
    key = $"{key}{BasketSuffix}";
    var redisDb = RedisConnection.Connection.GetDatabase();
    await redisDb.KeyExpireAsync(key, _expire);

    return await redisDb.StringGetAsync(key);
}

我理解你在 .KeyExpireAsync 调用中不使用 await 关键字的想法，但如果我正在编写这段代码，我肯定会像我一样 await证明。即发即弃是一种代码味道，可以很容易地避免。

从 Redis 检索多个键时死锁

Dead lock when retrieving several keys from Redis

c#

task-parallel-library

async-await

stackexchange.redis