How to use context in Go to implement automatic refresh of request result cache

How to use context in Go to implement automatic refresh of request result cache

Abstract:
In web application development, in order to improve user experience, sometimes we need to cache the results of some requests to reduce Access to databases or other services. However, the validity period of cached data is a problem. Expired cache may cause users to obtain expired data, resulting in erroneous display and operations. In this article, we will explore how to use Go's context package to implement the automatic refresh function of request result cache to ensure the timeliness of cached data.

1. What is the context package
   Go language provides a context package as a tool for transferring context information between coroutines. The Context type in the context package provides some methods and properties for controlling and canceling the execution of coroutines. When processing web requests, we can pass the context information of the request through the context package and control the execution of some related operations.
2. Implementing request result caching
   First, we need to define a cache structure to store the request results and their expiration time. The code is as follows:

type CacheItem struct {
    result      interface{}
    expireAt    time.Time
}

type Cache struct {
    cacheMap    map[string]CacheItem
    mutex       sync.RWMutex
}

In the above code, we use a map to store cache items, where the key is the unique identifier related to the request and the value is the cache item details (such as results and expiration time). To ensure concurrency safety, we use a mutex lock.

Next, we need to write a function to obtain cache data. This function first checks whether the request result exists in the cache and determines whether it has expired. If the cached result exists and has not expired, the cached data is returned directly. Otherwise, we need to make the actual request and cache the result. The code is as follows:

func (c *Cache) Get(key string) interface{} {
    c.mutex.RLock()
    defer c.mutex.RUnlock()

    item, ok := c.cacheMap[key]
    if ok && item.expireAt.After(time.Now()) {
        return item.result
    }

    // 发起请求并更新缓存
    result := makeRequest(key)
    c.cacheMap[key] = CacheItem{result: result, expireAt: time.Now().Add(time.Minute)}

    return result
}

In the above code, we use read locks to read cache items to ensure concurrency safety. If the cache item exists and has not expired, the cache result is returned directly; otherwise, we initiate an actual request and store the request result in the cache.

3. Refresh cache
   In order to ensure the timeliness of cached data, we need to refresh the cache regularly. In Go, we can use the WithDeadline function of the context package to set a deadline and automatically cancel the corresponding operation after the timeout. We can use this feature to automatically refresh the cache. The code is as follows:

func (c *Cache) RefreshCache(ctx context.Context, key string) {
    ticker := time.NewTicker(time.Minute)
    defer ticker.Stop()

    for {
        select {
        case <-ticker.C:
            result := makeRequest(key)
            c.mutex.Lock()
            c.cacheMap[key] = CacheItem{result: result, expireAt: time.Now().Add(time.Minute)}
            c.mutex.Unlock()
        case <-ctx.Done():
            return
        }
    }
}

In the above code, we use a Ticker object to regularly call the makeRequest function to update the cache. At the same time, we use the select statement to listen to the context cancellation signal to exit the refresh loop after the context is canceled. .

4. Usage Example
   Next, we will use a simple web application to demonstrate how to use the above cache implementation. The code is as follows:

package main

import (
    "context"
    "fmt"
    "net/http"
    "sync"
    "time"
)

type CacheItem struct {
    result   interface{}
    expireAt time.Time
}

type Cache struct {
    cacheMap map[string]CacheItem
    mutex    sync.RWMutex
}

func makeRequest(key string) interface{} {
    // 模拟请求耗时
    time.Sleep(time.Second)
    return fmt.Sprintf("result for %s", key)
}

func (c *Cache) Get(key string) interface{} {
    c.mutex.RLock()
    defer c.mutex.RUnlock()

    item, ok := c.cacheMap[key]
    if ok && item.expireAt.After(time.Now()) {
        return item.result
    }

    result := makeRequest(key)
    c.cacheMap[key] = CacheItem{result: result, expireAt: time.Now().Add(time.Minute)}

    return result
}

func (c *Cache) RefreshCache(ctx context.Context, key string) {
    ticker := time.NewTicker(time.Minute)
    defer ticker.Stop()

    for {
        select {
        case <-ticker.C:
            result := makeRequest(key)
            c.mutex.Lock()
            c.cacheMap[key] = CacheItem{result: result, expireAt: time.Now().Add(time.Minute)}
            c.mutex.Unlock()
        case <-ctx.Done():
            return
        }
    }
}

func main() {
    cache := &Cache{cacheMap: make(map[string]CacheItem)}

    http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
        ctx, cancel := context.WithDeadline(context.Background(), time.Now().Add(time.Second*5))
        defer cancel()

        key := r.URL.Path

        result := cache.Get(key)
        fmt.Fprintf(w, "%s: %s", key, result)

        // 启动刷新缓存的协程
        go cache.RefreshCache(ctx, key)
    })

    http.ListenAndServe(":8080", nil)
}

In the above example code, we define a simple HTTP server. When a request is received, the cached Get method is called to obtain the data and returned to the client. At the same time, we use the context package to create a context with a 5-second deadline and pass it to the RefreshCache method to control the refresh time of the cache.

Conclusion:
This article introduces how to use Go's context package to implement the automatic refresh function of the request result cache. By using cache structures and mutexes to ensure concurrency safety, and using the features of the context package to regularly refresh the cache, we can simply cache the request results and ensure the timeliness of the data. The above example code is only a simple demonstration. Actual use may require appropriate modification and optimization based on specific needs.

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