Entity Server
Serve entities
Libraries:
SimEvents
Description
The Entity Server block serves entities as they arrive. In a discrete-event simulation, a server stores entities for a length of time, called service time, and then attempts to output the entity. During the service period, the block is said to be serving the entity that it stores. The block can serve multiple entities simultaneously and output each entity through the output port, unless the port is blocked. When the block permits preemption, an entity in the server can depart early through a second port.
To customize actions when entities enter, complete service, exit, and are blocked or
preempted by the block, enter MATLAB® code in the Entry action
, Service complete
action
, Exit action
, Blocked action
,
or Preempt action
field of the Event actions
tab. For more information, see Events and Event Actions.
Examples
M/M/1 Queuing System
Model a single-queue single-server system with a single traffic source and an infinite storage capacity. In the notation, the M stands for Markovian; M/M/1 means that the system has a Poisson arrival process, an exponential service time distribution, and one server. Queuing theory provides exact theoretical results for some performance measures of an M/M/1 queuing system and this model makes it easy to compare empirical results with the corresponding theoretical results.
M/D/1 Queuing System
Model a single-queue single-server system that has a Poisson arrival process and a server with constant service time. The queue has an infinite storage capacity. In the notation, the M stands for Markovian; M/D/1 means that the system has a Poisson arrival process, a deterministic service time distribution, and one server.
Modeling Hybrid Systems - Tank Filling
A hybrid system with both continuous time and discrete event sections. The discrete event part models tanks, represented by entities, which are being queued and need to be filled up. Each tank has a "Capacity" attribute. The continuous time part models the process of filling up a tank, modeled by an Integrator. When a tank is filled to capacity, this event can be detected by a Hit Crossing block, which will generate a message corresponding to this event. The generated message will trigger the server to release the tank.
Using Entity Priority to Sequence Departures
Use entity priority to sequence entity departures when multiple entities are available to depart. The example models an airport check-in counter where passengers arrive to be checked in. Passengers can have either First-Class, Business Class, or Economy Class reservations, modeled using entity priority values 1, 2 and 3 respectively.
Using Custom Visualization for Entities
These examples show how you can create MATLAB®-based custom visualization for entities. The example illustrates the visualization of a restaurant layout with customer entities entering, dining, and leaving.
Ports
Input
Port_1 — Input entity
scalar | vector | matrix
Input entity that carries scalar, bus, or vector data to enter the server.
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
| Boolean
| enumerated
| bus
| string
| fixed point
Port_2 — Input signal port for service time source
scalar
Input signal port to determine service time.
Dependencies
This port is visible when Service time source
is set to Signal port
.
Data Types: double
Output
Port_1 — Output entity
scalar | vector | matrix
Output entity port for entities exiting the server.
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
| Boolean
| enumerated
| bus
| string
| fixed point
Port_d — Number of entities that have departed the block
scalar
Number of entities that have departed the block.
Dependencies
To enable this port, click the Statistics tab and select the box labeled Number of entities departed, d.
Data Types: double
Port_n — Number of entities that have not yet departed the block
scalar
Number of entities that have not yet departed the block.
Dependencies
To enable this port, click the Statistics tab and select the box labeled Number of entities in block, n.
Data Types: double
Port_pe — Pending entity in block
off (default) | on
Selecting this check box outputs the value 1
for a
pending entity in the block, and 0
otherwise.
Dependencies
To enable this port, select the Statistics > Pending entity in block, pe.
Data Types: double
Port_np — Number of pending entities
off (default) | on
Selecting this check box outputs the number of pending entities in the block.
Dependencies
To enable this port, select the Statistics > Number of pending entities, np.
Data Types: double
Port_w — Average wait time for entities in the block
scalar
Average wait time for entities in the block.
Dependencies
To enable this port, click the Statistics tab and select the box labeled Average wait, w.
Data Types: double
Port_util — Outputs the average time the server is occupied
scalar
Average time the server is occupied.
Dependencies
To enable this port, click the Statistics tab and select the box labeled Utilization, util.
Data Types: double
Port_p — Outputs the number of preempted entities
scalar
Number of preempted entities.
Dependencies
To enable this port, first click the Preemption tab, then click Statistics tab and select the box labeled Number of entities preempted, p.
Data Types: double
Port_ex — Number of entities extracted
scalar
Number of entities that are pulled out of this block.
Dependencies
To enable this port, click the Statistics tab and select the box labeled Number of entities extracted, ex.
Data Types: double
Parameters
Capacity — Specify the capacity of the server
1
(default) | scalar
Specify the number of entities the block can serve simultaneously.
Programmatic Use
Block Parameter:
Capacity |
Type: character vector |
Values: '1' |
scalar |
Default:
'1' |
Service time source — Choose the source to specify the service time
Dialog
(default) | Signal port
| Attribute
| MATLAB action
Determine the source that specifies the service time.
You can select:
Dialog
Enter the constant value in the Service time value parameter.
Signal port
Connect a time source to the resulting signal port.
Attribute
Enter the name of the attribute that contains data to be interpreted as service.
MATLAB action
In the Service time action section, enter MATLAB code to vary the service time. Assign the variable dt, which the model uses as service time.
Programmatic Use
Block Parameter:
ServiceTimeSource |
Type: character vector |
Values:
'Dialog' | 'Signal port'
| 'Attribute' | 'MATLAB
action' |
Default:
'Dialog' |
Service time attribute name — Specify service time source attribute name
ServiceTime
(default) | character vector
Determine the name of the attribute that is used as the service time value.
Dependencies
This parameter is visible when Service time
source is set to
Attribute
.
Programmatic Use
Block Parameter:
ServiceTimeAttributeName |
Type: character vector |
Values:
'ServiceTime' | character vector |
Default:
'ServiceTime' |
Service time value — Specify the value of the service time
1
(default) | scalar
Tunable: Yes
Dependencies
This parameter is visible when Service time
source is set to
Dialog
.
Programmatic Use
Block Parameter:
ServiceTimeValue |
Type: character vector |
Values:
'1.0' | scalar |
Default:
'1.0' |
Service time action — Specify service time
dt = rand(1,1)
(default) | MATLAB code
Use MATLAB code to specify service time. dt
specifies
the service time. You can manually specify dt
or use
Insert pattern button to specify service time from
a repeating sequence or from a distribution. For an example, see Count Simultaneous Departures from a Server.
Dependencies
This parameter is visible when Service time
source is set to MATLAB
action
.
Programmatic Use
Block Parameter:
ServiceTimeAction |
Type: character vector |
Values: MATLAB code |
Default: 'dt =
rand(1,1);' |
Event action — Specify the behavior of the entity in certain events
Entry
(default) | Service complete
| Exit
| Blocked
| Preempt
Specify the behavior of the entity in certain events. Define the behavior in the Event action parameter. The Entry and the Exit actions are called just after the entity entry and just before entity exit. The Service complete action is called after the completion of the entity service. The Blocked action is called after an entity is blocked. The Preempt is called after the preemption.
Note
If an event action changes an entity, related block behavior such as resorting a priority queue, and rescheduling of any events, will occur after the event action has fully finished and returned.
Programmatic Use
Block Parameter:
EntryAction, ServiceCompleteAction, ExitAction,
BlockedAction, PreemptAction |
Type: character vector |
Values: MATLAB code |
Default:
'' |
Permit preemption based on attribute — Enable preemption of entities
off
(default) |
on
Select this check box if you want to allow preemption of entities. Preemption is the replacement of an entity in a server block by an entity that satisfies certain criteria. Selecting this check box enables these parameters:
Sorting attribute name in the Preemption tab
Sorting direction in the Preemption tab
Write residual time to attribute in the Preemption tab
Number of entities preempted, p in the Statistics tab
For an example, see Task Preemption in a Multitasking Processor.
Programmatic Use
Block Parameter:
PermitPreemptionBasedOnAttribute |
Type: character vector |
Values: 'on'
| 'off' |
Default:
'off' |
Sorting attribute name — Specify the name of the attribute used to determine the priority
entity
| entitySys.priority
| character vector
Specify the name of the attribute used to determine the priority.
Dependencies
This parameter is visible when the Permit preemption based on attribute box is selected.
Programmatic Use
Block Parameter:
SortingAttributeName |
Type: character vector |
Values:
'entity' |
'entitySys.priority' | character
vector |
Default:
'entity' |
Sorting direction — Choose the direction of sorting the entities
Ascending
(default) | Descending
Specify if the entities are sorted in ascending
or descending
order.
ascending
— Sorting entities with smaller key values to have a higher prioritydescending
— Sorting entities with greater key values to have a higher priority
Dependencies
This parameter is visible when the Permit preemption based on attribute box is selected.
Programmatic Use
Block Parameter:
SortingDirection |
Type: character vector |
Values:
'Ascending' |
'Descending' |
Default:
'Ascending' |
Write residual time to attribute — Save the residual service time from a preempted entity to an attribute
off
(default) |
on
Dependencies
This parameter is visible when the Permit preemption based on attribute box is selected.
Programmatic Use
Block Parameter:
WriteResidualTimeToAttribute |
Type: character vector |
Values: 'on'
| 'off' |
Default:
'off' |
Residual time attribute name — Specify the name of the attribute to contain the residual service time of a preempted entity
ResidualTime
(default) | character vector
Dependencies
This parameter is visible when the Write residual time to attribute box is selected.
Programmatic Use
Block Parameter:
ResidualTimeAttributeName |
Type: character vector |
Values:
'ResidualTime' | character vector |
Default:
'ResidualTime' |
Number of entities departed, d — Outputs the number of entities that have departed the block
off
(default) |
on
Number of entities that have departed the block.
Programmatic Use
Block Parameter:
NumberEntitiesDeparted |
Type: character vector |
Values: 'on'
| 'off' |
Default:
'off' |
Number of entities in block, n — Outputs the number of entities present in the block, that are yet to depart
off
(default) |
on
Number of entities present in the block that are yet to depart.
Programmatic Use
Block Parameter:
NumberEntitiesInBlock |
Type: character vector |
Values: 'on'
| 'off' |
Default:
'off' |
Pending entity in block, pe — Pending entities
off
(default) | on
Indicates whether an entity that is yet to depart is present in the block.
The value is 1
for a pending entity, and
0
otherwise.
Programmatic Use
Block Parameter:
PendingEntityPresentInBlock |
Type: character vector |
Values: 'on'
| 'off' |
Default:
'off' |
Number of pending entities, np — Number of Pending entities
off
(default) | on
Outputs the number of pending entities the block has served that are yet to depart.
Programmatic Use
Block Parameter:
NumberEntitiesPending |
Type: character vector |
Values: 'on'
| 'off' |
Default:
'off' |
Average wait, w — Outputs the average wait time
off
(default) |
on
Sum of the wait times for entities departed the block divided by their total number. Wait time is the duration between the Entity Server block entry and exit of an entity. For more information, see Interpret SimEvents Models Using Statistical Analysis.
Programmatic Use
Block Parameter:
AverageWait |
Type: character vector |
Values: 'on'
| 'off' |
Default:
'off' |
Utilization, util — Outputs the average time the server is occupied
off
(default) |
on
Average time the server is occupied. The block calculates this time as the ratio of the total wait time for entities to the server capacity multiplied by the total simulation time.
Wait time is the duration between the Entity Server block entry and exit of an entity. Total wait time is the sum of the wait times for entities departed the block.
Programmatic Use
Block Parameter:
Utilization |
Type: character vector |
Values: 'on'
| 'off' |
Default:
'off' |
Number of entities preempted, p — Outputs the number of preempted entities
off
(default) | on
Outputs the number of preempted entities. Preemption is the replacement of an entity in a server block by an entity that satisfies certain criteria.
Dependencies
This check box appears if the Permit preemption based on attribute check box is selected.
Programmatic Use
Block Parameter:
NumberEntitiesPreempted |
Type: character vector |
Values: 'on'
| 'off' |
Default:
'off' |
Number of entities extracted, ex — Number of entities extracted from this block
off
(default) | on
Outputs the number of extracted entities which are pulled out from this block by the Entity Find block. If an entity is being served during the extraction, the service is terminated. If an attribute that defines the service time and it is modified by the Entity Find block, service time does not change. When an entity is extracted, Number of entities departed, d, Number of entities in block, n, Average wait, w, and Utilization, util statistics are updated accordingly. For more information about finding and extracting entities, see Find and Extract Entities in SimEvents Models.
Programmatic Use
Block Parameter:
NumEntitiesExtracted |
Type: character vector |
Values: 'on'
| 'off' |
Default:
'off' |
Version History
Introduced in R2016a
See Also
Entity Generator | Entity Multicast | Entity Gate | Composite Entity Creator | Composite Entity Splitter | Entity Input Switch | Entity Output Switch | Entity Queue | Discrete-Event Chart | Multicast Receive Queue | Entity Multicast | Entity Replicator | Entity Terminator | MATLAB Discrete-Event System | Resource Acquirer | Resource Releaser | Resource Pool
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