MemoryStoreQueue
Provides access to a queue within MemoryStore. A queue is a data structure that provides temporary storage for arbitrary items (up to the maximum item size -- see MemoryStore Limits). Each queue item has a numeric priority: MemoryStore retrieves items with higher priority from the queue first, and it retrieves Items with the same priority in order of addition.
Items in the queue can optionally be set to expire after a certain amount of time. Expired items simply disappear from the queue as if they were never added.
Summary
Methods
Adds an item to the queue.
Reads one or more items from the queue.
Removes an item or items previously read from the queue.
Properties
Methods
AddAsync
Adds an item to the queue.
Parameters
The value of the item to add to the queue.
Item expiration time, in seconds, after which the item will be automatically removed from the queue.
Item priority. Items with higher priority are retrieved from the queue before items with lower priority.
Returns
ReadAsync
Reads one or more items from the queue as a single atomic operation.
This method does not automatically delete the returned items from the queue but makes them invisible to other ReadAsync calls for the period of the invisibility timeout. The items must be explicitly removed from the queue with MemoryStoreQueue:RemoveAsync() before the invisibility timeout expires. The invisibility timeout defaults to 30 seconds unless a different value was provided in MemoryStoreService:GetQueue().
Parameters
Number of items to read. The maximum allowed value of this parameter is 100.
Controls the behavior of the method in the case the queue has fewer than count items: if set to false the method returns all available items; if set to true, it returns no items. The default value is false.
The duration, in seconds, for which the method will wait if the required number of items is not immediately available in the queue. Reads are attempted every two seconds during this period. This parameter can be set to zero to indicate no wait. If this parameter is not provided or set to -1, the method will wait indefinitely.
Returns
A tuple of two elements. The first element is an array of item values read from the queue. The second element is a string identifier that should be passed to MemoryStoreQueue:RemoveAsync() to permanently remove these items from the queue.
Code Samples
The following code sample demonstrates using MemoryStoreQueue:ReadAsync() and MemoryStoreQueue:RemoveAsync() to reliably read, process, and remove items from a queue. Though this process can be as complicated as necessary, this example simply sets a flag in the corresponding data store item, which guarantees that every item will eventually be processed even if some of the calls encounter errors or the server crashes:
- If MemoryStoreQueue:ReadAsync() fails, no items are retrieved from the queue. An item will be picked up for processing during the next iteration of the loop.
- If MemoryStoreQueue:ReadAsync() succeeds but DataStoreService:UpdateAsync() fails, the item stays invisible until the queue's invisibility timeout expires, causing the item becoming visible again to be returned in a future loop iteration.
- Similarly, if MemoryStoreQueue:RemoveAsync() fails, the item will become visible again in the future and will be processed again.
Depending on where the failure happens, it's possible that an item will be processed more than once. You should account for that like the following code sample, in which the end result is the same even if DataStoreService:UpdateAsync() is invoked multiple times.
local MemoryStoreService = game:GetService("MemoryStoreService")
local DataStoreService = game:GetService("DataStoreService")
local queue = MemoryStoreService:GetQueue("PlayerQueue")
local dataStore = DataStoreService:GetDataStore("PlayerStore")
while true do
pcall(function()
-- wait for an item to process
local items, id = queue:ReadAsync(1, false, 30)
-- check if an item was retrieved
if #items > 0 then
-- mark the item as processed
dataStore:UpdateAsync(items[0], function(data)
data = data or {}
data.processed = 1
return data
end)
-- remove the item from the queue
queue:RemoveAsync(id)
end
end)
endRemoveAsync
Removes an item or items previously read from the queue. This method uses the identifier returned by MemoryStoreQueue:ReadAsync() to identify the items to remove. If called after the invisibility timeout has expired, the call has no effect.
Parameters
Identifies the items to delete. Use the value returned by MemoryStoreQueue:ReadAsync().
Returns
Code Samples
The following code sample demonstrates using MemoryStoreQueue:ReadAsync() and MemoryStoreQueue:RemoveAsync() to reliably read, process, and remove items from a queue. Though this process can be as complicated as necessary, this example simply sets a flag in the corresponding data store item, which guarantees that every item will eventually be processed even if some of the calls encounter errors or the server crashes:
- If MemoryStoreQueue:ReadAsync() fails, no items are retrieved from the queue. An item will be picked up for processing during the next iteration of the loop.
- If MemoryStoreQueue:ReadAsync() succeeds but DataStoreService:UpdateAsync() fails, the item stays invisible until the queue's invisibility timeout expires, causing the item becoming visible again to be returned in a future loop iteration.
- Similarly, if MemoryStoreQueue:RemoveAsync() fails, the item will become visible again in the future and will be processed again.
Depending on where the failure happens, it's possible that an item will be processed more than once. You should account for that like the following code sample, in which the end result is the same even if DataStoreService:UpdateAsync() is invoked multiple times.
local MemoryStoreService = game:GetService("MemoryStoreService")
local DataStoreService = game:GetService("DataStoreService")
local queue = MemoryStoreService:GetQueue("PlayerQueue")
local dataStore = DataStoreService:GetDataStore("PlayerStore")
while true do
pcall(function()
-- wait for an item to process
local items, id = queue:ReadAsync(1, false, 30)
-- check if an item was retrieved
if #items > 0 then
-- mark the item as processed
dataStore:UpdateAsync(items[0], function(data)
data = data or {}
data.processed = 1
return data
end)
-- remove the item from the queue
queue:RemoveAsync(id)
end
end)
end