/// <summary>
/// Read a value from the cache
/// </summary>
/// <typeparam name="T">Type to read</typeparam>
/// <param name="key">Key</param>
/// <param name="value">Value</param>
/// <param name="notFound">Create T if not found, null to not do this. Item1 = value, Item2 = expiration.</param>
public async Task <CachedItem <T> > Get <T>(string key, Func <Task <CachedItem <T> > > notFound) where T : class
{
using (var lockRead = cacheTimerLock.LockRead())
{
if (cache.TryGetValue(key, out KeyValuePair <DateTime, object> cacheValue))
{
return(new CachedItem <T>((T)cacheValue.Value, cacheValue.Key));
}
}
// most likely the callback needs to make a network request, so don't do it in a lock
// it's ok if multiple calls stack on the same cache key, the last one to finish will win
CachedItem <T> newItem = await notFound();
// don't add null values to the cache
if (newItem.Value != null)
{
using (var lockWrite = cacheTimerLock.LockWrite())
{
cache[key] = new KeyValuePair <DateTime, object>(newItem.Expiration, newItem.Value);
}
}
return(newItem);
}
/// <summary>
/// Get cache of symbols metadata and put into a dictionary. This method looks in the cache first, and if found, returns immediately, otherwise makes a network request and puts it in the cache
/// </summary>
/// <param name="api">Exchange API</param>
/// <returns>Dictionary of symbol name and market, or null if there was an error</returns>
public static async Task <Dictionary <string, ExchangeMarket> > GetExchangeMarketDictionaryFromCacheAsync(this ExchangeAPI api)
{
await new SynchronizationContextRemover();
CachedItem <Dictionary <string, ExchangeMarket> > cacheResult = await api.Cache.Get <Dictionary <string, ExchangeMarket> >(nameof(GetExchangeMarketDictionaryFromCacheAsync), async() =>
{
try
{
Dictionary <string, ExchangeMarket> symbolsMetadataDictionary = new Dictionary <string, ExchangeMarket>(StringComparer.OrdinalIgnoreCase);
IEnumerable <ExchangeMarket> symbolsMetadata = await api.GetMarketSymbolsMetadataAsync();
// build a new lookup dictionary
foreach (ExchangeMarket symbolMetadata in symbolsMetadata)
{
symbolsMetadataDictionary[symbolMetadata.MarketSymbol] = symbolMetadata;
}
// return the cached dictionary for 4 hours
return(new CachedItem <Dictionary <string, ExchangeMarket> >(symbolsMetadataDictionary, CryptoUtility.UtcNow.AddHours(4.0)));
}
catch// (Exception ex)
{
// if the network goes down this could log quite a lot of exceptions...
//Logger.Error(ex);
return(new CachedItem <Dictionary <string, ExchangeMarket> >());
}
});
if (cacheResult.Found)
{
return(cacheResult.Value);
}
return(null);
}
/// <summary>
/// Gets the exchange market from this exchange's SymbolsMetadata cache. This will make a network request if needed to retrieve fresh markets from the exchange using GetSymbolsMetadataAsync().
/// Please note that sending a symbol that is not found over and over will result in many network requests. Only send symbols that you are confident exist on the exchange.
/// </summary>
/// <param name="marketSymbol">The market symbol. Ex. ADA/BTC. This is assumed to be normalized and already correct for the exchange.</param>
/// <returns>The ExchangeMarket or null if it doesn't exist in the cache or there was an error</returns>
public virtual async Task <ExchangeMarket> GetExchangeMarketFromCacheAsync(string marketSymbol)
{
try
{
// *NOTE*: custom caching, do not wrap in CacheMethodCall...
// *NOTE*: vulnerability exists where if spammed with not found symbols, lots of network calls will happen, stalling the application
// TODO: Add not found dictionary, or some mechanism to mitigate this risk
// not sure if this is needed, but adding it just in case
await new SynchronizationContextRemover();
CachedItem <Dictionary <string, ExchangeMarket> > cacheResult = await Cache.Get <Dictionary <string, ExchangeMarket> >(nameof(GetExchangeMarketFromCacheAsync), null);
if (cacheResult.Found && cacheResult.Value.TryGetValue(marketSymbol, out ExchangeMarket market))
{
return(market);
}
// try again with a fresh request
Cache.Remove(nameof(GetExchangeMarketFromCacheAsync));
Cache.Remove(nameof(GetMarketSymbolsMetadataAsync));
cacheResult = await Cache.Get <Dictionary <string, ExchangeMarket> >(nameof(GetExchangeMarketFromCacheAsync), async() =>
{
Dictionary <string, ExchangeMarket> symbolsMetadataDictionary = new Dictionary <string, ExchangeMarket>(StringComparer.OrdinalIgnoreCase);
IEnumerable <ExchangeMarket> symbolsMetadata = await GetMarketSymbolsMetadataAsync();
// build a new lookup dictionary
foreach (ExchangeMarket symbolMetadata in symbolsMetadata)
{
symbolsMetadataDictionary[symbolMetadata.MarketSymbol] = symbolMetadata;
}
// return the cached dictionary for 4 hours
return(new CachedItem <Dictionary <string, ExchangeMarket> >(symbolsMetadataDictionary, CryptoUtility.UtcNow.AddHours(4.0)));
});
// attempt to lookup one more time in the dictionary
if (cacheResult.Found && cacheResult.Value.TryGetValue(marketSymbol, out market))
{
return(market);
}
}
catch
{
// TODO: Report the error somehow, for now a failed network request will just return null symbol which will force the caller to use default handling
}
return(null);
}
/// <summary>
/// Read a value from the cache
/// </summary>
/// <typeparam name="T">Type to read</typeparam>
/// <param name="key">Key</param>
/// <param name="value">Value</param>
/// <param name="notFound">Create T if not found, null to not do this. Item1 = value, Item2 = expiration.</param>
public async Task <CachedItem <T> > GetOrCreate <T>(string key, Func <Task <CachedItem <T> > > notFound) where T : class
{
CachedItem <T> newItem = default;
cacheTimerLock.EnterReadLock();
try
{
if (cache.TryGetValue(key, out KeyValuePair <DateTime, object> cacheValue))
{
return(new CachedItem <T>((T)cacheValue.Value, cacheValue.Key));
}
}
finally
{
cacheTimerLock.ExitReadLock();
}
if (notFound == null)
{
return(new CachedItem <T>());
}
// most likely the callback needs to make a network request, so don't do it in a lock
// it's ok if multiple calls stack on the same cache key, the last one to finish will win
newItem = await notFound();
// don't add null values to the cache
if (newItem.Value != null)
{
cacheTimerLock.EnterWriteLock();
try
{
cache[key] = new KeyValuePair <DateTime, object>(newItem.Expiration, newItem.Value);
}
finally
{
cacheTimerLock.ExitWriteLock();
}
}
return(newItem);
}