public void When_Composing_ToCachedString_CreateFromCachedString_Is_Identity(double rssi)
{
// arrange
const string gatewayId = "foo";
var initial = new PreferredGatewayTableItem(gatewayId, rssi);
// act
var result = PreferredGatewayTableItem.CreateFromCachedString(initial.ToCachedString());
// assert
Assert.Equal(initial.GatewayID, result.GatewayID);
Assert.Equal(initial.Rssi, result.Rssi);
}
private async Task <PreferredGatewayResult> ComputePreferredGateway(IPipelineExecutionContext context)
{
var computationId = Guid.NewGuid().ToString();
var fcntUp = context.Request.ClientFCntUp;
var devEUI = context.DevEUI;
var rssi = context.Request.Rssi.Value;
// 1. Add request to list `preferred_gateway:deviceID:fcnt`, timeout: 5min
// List item: gatewayid, rssi, insertTime
var item = new PreferredGatewayTableItem(context.Request.GatewayId, rssi);
var listCacheKey = LoRaDevicePreferredGateway.PreferredGatewayFcntUpItemListCacheKey(devEUI, fcntUp);
this.cacheStore.ListAdd(listCacheKey, item.ToCachedString(), TimeSpan.FromMinutes(REQUEST_LIST_CACHE_DURATION_IN_MINUTES));
this.log.LogInformation("Preferred gateway {devEUI}/{fcnt}: added {gateway} with {rssi}", devEUI, fcntUp, context.Request.GatewayId, rssi);
// 2. Wait for the time specified in receiveInterval (default 200ms). Optional: wait less if another requests already started
await Task.Delay(this.receiveInterval);
// 3. Check if value was already calculated
var preferredGateway = LoRaDevicePreferredGateway.LoadFromCache(this.cacheStore, devEUI);
if (preferredGateway != null)
{
if (preferredGateway.FcntUp >= fcntUp)
{
return(new PreferredGatewayResult(devEUI, fcntUp, preferredGateway));
}
}
// 4. To calculated need to adquire a lock
var preferredGatewayLockKey = $"preferredGateway:{devEUI}:lock";
for (var i = 0; i < MAX_ATTEMPTS_TO_RESOLVE_PREFERRED_GATEWAY; i++)
{
if (await this.cacheStore.LockTakeAsync(preferredGatewayLockKey, computationId, TimeSpan.FromMilliseconds(200), block: false))
{
try
{
preferredGateway = LoRaDevicePreferredGateway.LoadFromCache(this.cacheStore, devEUI);
if (preferredGateway == null || preferredGateway.FcntUp < fcntUp)
{
var items = this.cacheStore.ListGet(listCacheKey).Select(x => PreferredGatewayTableItem.CreateFromCachedString(x));
// if no table item was found (redis restarted, or delayed processing)?
// Return error, we don't want to save a value for each gateway or overwrite with a delayed request
var winner = items?.OrderByDescending(x => x.Rssi).FirstOrDefault();
if (winner == null)
{
this.log.LogError("Could not resolve closest gateway in {devEUI} and {fcntUp}", devEUI, fcntUp);
return(new PreferredGatewayResult(devEUI, fcntUp, "Could not resolve closest gateway"));
}
preferredGateway = new LoRaDevicePreferredGateway(winner.GatewayID, fcntUp);
LoRaDevicePreferredGateway.SaveToCache(this.cacheStore, context.DevEUI, preferredGateway);
this.log.LogInformation("Resolved preferred gateway {devEUI}/{fcnt}: {gateway} with {rssi}", devEUI, fcntUp, context.Request.GatewayId, rssi);
}
}
finally
{
this.cacheStore.LockRelease(preferredGatewayLockKey, computationId);
}
}
else
{
// We couldn't get lock
// wait a bit and try to get result
await Task.Delay(Math.Max(50, this.receiveInterval / 4));
preferredGateway = LoRaDevicePreferredGateway.LoadFromCache(this.cacheStore, context.DevEUI);
}
if (preferredGateway != null)
{
if (preferredGateway.FcntUp >= fcntUp)
{
return(new PreferredGatewayResult(devEUI, fcntUp, preferredGateway));
}
}
}
this.log.LogError("Could not resolve closest gateway in {devEUI} and {fcntUp}", devEUI, fcntUp);
return(new PreferredGatewayResult(devEUI, fcntUp, "Could not resolve closest gateway"));
}