simmer 4.2.1
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The 4.2.1 release of simmer, the Discrete-Event Simulator for R, is on CRAN with quite interesting new features and fixes. As discussed in the mailing list, there is a way to handle the specific case in which an arrival is rejected because a queue is full:
library(simmer) reject <- trajectory() %>% log_("kicked off...") patient <- trajectory() %>% seize("nurse", continue=FALSE, reject=reject) %>% log_("nurse seized") %>% timeout(5) %>% release("nurse") %>% log_("nurse released") env <- simmer() %>% add_resource("nurse", 1, 0) %>% add_generator("patient", patient, at(0, 1)) %>% run() ## 0: patient0: nurse seized ## 1: patient1: kicked off... ## 5: patient0: nurse released
But as Tom Lawton pointed out, until now, there was no way of handling any alternative path for an arrival that was preempted and “kicked off” from a resource. This mechanism has been implemented into the new handle_unfinished()
activity:
patient <- trajectory() %>% handle_unfinished(reject) %>% seize("nurse") %>% log_("nurse seized") %>% timeout(5) %>% release("nurse") %>% log_("nurse released") env <- simmer() %>% add_resource("nurse", 1, 0, preemptive=TRUE, queue_size_strict=TRUE) %>% add_generator("LowPrio_patient", patient, at(0), priority=0) %>% add_generator("HighPrio_patient", patient, at(1), priority=10) %>% run() ## 0: LowPrio_patient0: nurse seized ## 1: HighPrio_patient0: nurse seized ## 1: LowPrio_patient0: kicked off... ## 6: HighPrio_patient0: nurse released
Note that such a mechanism is more general, because it also covers the first scenario:
env <- simmer() %>% add_resource("nurse", 1, 0) %>% add_generator("patient", patient, at(0, 1)) %>% run() ## 0: patient0: nurse seized ## 1: patient1: kicked off... ## 5: patient0: nurse released
Whenever rejection (or preemption) happens and it is catched by the appropriate handler, the new getter get_seized()
may be useful to know which resource was abandoned.
Finally, the readership may find interesting the new section about the implementation of state-dependent service rates in the Queueing Systems vignette. See below for a complete list of changes.
New features:
- New
handle_unfinished()
activity sets a drop-out trajectory for unfinished arrivals, i.e., those dropped from a resource (due to preemption, resource shrinkage or a rejectedseize
) or those thatleave
a trajectory (#178 addressing #177). - New
release_all()
andrelease_selected_all()
activities automatically retrieve the amount of resources seized and release it (#180 addressing #25). - New
get_seized()
andget_seized_selected()
getters allow an arrival to retrieve the amount of resources seized (#180 addressing #179). - New
stop_if()
activity sets a conditional breakpoint (#181 addressing #100).
Minor changes and fixes:
- Fix performance issues in data sources (#176).
- Update CITATION.
- Fix monitored activity for preempted arrivals (as part of #178).
- Fix seizes/releases with a null amount (as part of #180).
- Rename internal status codes (as part of #181).
- Provide more context on error or warning (as part of #181).
- Extend the
Queueing Systems
vignette with a section about state-dependent service rates. - Fix performance issues in getters (#183).
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