/// <summary>
/// Must call this periodically to move work items from priority queue to pending queue
/// </summary>
public bool PrepareNextWorkItem()
{
//harvest zombies every 5 minutes
var now = DateTime.UtcNow;
var ts = now - harvestTime;
if (ts.TotalMinutes > 5)
{
HarvestZombies();
harvestTime = now;
}
using (var disposableClient = clientManager.GetDisposableClient <SerializingRedisClient>())
{
var client = disposableClient.Client;
//1. get next workItemId, or return if there isn't one
var smallest = client.ZRangeWithScores(workItemIdPriorityQueue, 0, 0);
if (smallest == null || smallest.Length <= 1 ||
RedisNativeClient.ParseDouble(smallest[1]) == CONVENIENTLY_SIZED_FLOAT)
{
return(false);
}
var workItemId = client.Deserialize(smallest[0]) as string;
// lock work item id
var lockKey = queueNamespace.GlobalLockKey(workItemId);
using (var disposableLock = new DisposableDistributedLock(client, lockKey, lockAcquisitionTimeout, lockTimeout))
{
// if another client has queued this work item id,
// then the work item id score will be set to CONVENIENTLY_SIZED_FLOAT
// so we return false in this case
var score = client.ZScore(workItemIdPriorityQueue, smallest[0]);
if (score == CONVENIENTLY_SIZED_FLOAT)
{
return(false);
}
using (var pipe = client.CreatePipeline())
{
var rawWorkItemId = client.Serialize(workItemId);
// lock work item id in priority queue
pipe.QueueCommand(
r =>
((RedisNativeClient)r).ZAdd(workItemIdPriorityQueue, CONVENIENTLY_SIZED_FLOAT, smallest[0]));
// track dequeue lock id
pipe.QueueCommand(r => ((RedisNativeClient)r).SAdd(dequeueIdSet, rawWorkItemId));
// push into pending set
pipe.QueueCommand(r => ((RedisNativeClient)r).LPush(pendingWorkItemIdQueue, rawWorkItemId));
pipe.Flush();
}
}
}
return(true);
}