However, if the previous block that is connected to the queue is set to “Push Protocol” and pushes an agent into a full queue with enabled preemption, then this new agent will exit the queue via outPreempted port. However, there is a third option for handling this scenario and that’s to enable “ preemption” for the queue.Īs mentioned before If the queue is full, it won’t let a new agent to enter it. Therefore, if the previous block that is connected to the queue is set to “Push Protocol” (e.g., Source) and pushes an agent into a full queue, AnyLogic will throw an exception message like below:Īs shown in the picture above AnyLogic suggests two options for this situation: increasing the capacity of the subsequent blocks (including the queue itself) or using Pull protocol. This default setting guaranties that the arrival mechanism defined by the modeler is not changed unintentionally due to lack of available capacity in the flowchart. As shown in the example below, if a queue with a capacity of 9 is full, the incoming agent will pile up in the previous blocks (queue 3).Īlthough, “Source” supports pull protocol, by default it is set to “push” agents out. AnyLogic Blocks such as Source, Enter, Delay, Pickup, Dropoff, Seize, Batch, Unbatch, Combine support “pull” protocol. In a “pull” protocol, flowchart objects will stop and wait until the next objects are ready. Since the “in” port of the queue is blocked in a full queue, by default the previous blocks will hold the agents assuming they have enough capacity available (pull protocol). If the queue is full (based on its capacity), it won’t let a new agent to enter it. If (!waitingAgent.agent_type.Queue block helps us model a queue of agents that are waiting to be processed in the next block of flowchart. there should be one agent in 'wait' and this will In this case, the implementation was done using a Wait block.Īdditionally on enter action of the seize block contains following code: List toFree = new ArrayList() Having looked it some more, it appears the queue size on Seize can not be zero. Why not separate the two? What you could do is put a Queue object before the Seize with A=1, B=2, C=3 ordering, then set the queue size of the Seize object to 0 and put the pre-emption priorities (A,B=1 C=2) into the Seize task priority field like you've done here. The flowchart of the described queue I’m trying to model is shown on the image with some red lines trying to explain intuitively (but wrong) what I’m trying to do: ![]() I tried using the outPreempted port of the Seize block to add a moveTo block to move the agent to the waiting area, but this port seems to work only when preemption causes to end the task (terminate serving option). When the task preempt, I need to move the current ship that is using the dock, to a waiting area, and when the task that caused the preemptions ends, the ship that preempted, must return to where the static resource is (the dock) and resume its delay block.Shows the issue of having the same priority for queue and preemption How can I separate the priorities “ratings” for the queue from the priorities used to determine preemption? The priorities for preemption should be: Ship A and B with priority 1 and Ship C with priority 2. This means that the priorities defined in the “Task priority” field are valid to define the queue order of attention but not for preemption. The task of unloading the ship (the dock’s task when seized) must preempt when ship C arrives BUT not when ship A or B arrives.Now I need to model the following two behaviors related to preemption: The queue has three types of agents A, B, and C which have priorities 1, 2, and 3 respectively (this means that ship C has priority in the queue to utilize the dock). ![]() I’m trying to model a queue of ships that utilize a static resource which is a single dock (using flowcharts).
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