# simmer 3.6.2

## Minor changes and fixes:

• Update “The Bank Tutorial: Part I” vignette (@nacnudus in #90).
• Fix trap()’s handler cloning and associated test (#91).
• Apply select()’s policy also when resources is a function (#92).
• Accept dynamic timeouts in batches (#93).
• Change rollback()’s default behaviour to times=Inf, i.e., infinite loop (#95).
• Stop and throw an error when timeout() returns a missing value (#96 and #97).
• Fix memory management: resetting the environment was clearing but not deallocating memory (#98, fixed in #99).
• Fix object destruction: workaround for tidyverse/magrittr#146 (#98, fixed in effcb6b).

# simmer 3.6.1

## Minor changes and fixes:

• Recycle logical indexes when subsetting (2526e75).
• Implement replacement operators, [<- and [[<- (#88).
• Provide rep() S3 method for trajectories (7fa515e).
• Remove plotting functions (bb9656b), deprecated since v3.6.0. The new simmer.plot package (on CRAN) already covers these features among others.
• Don’t evaluate vignette chunks if Suggests are not installed (e40e5b6).
• Rewrite DESCRIPTION (3f26516).
• Add an every parameter to the from_to() convenience function (9d68887).

# simmer 3.6.0

## New features:

• New subsetting operators, [ and [[, for trajectories (1847898). Think about trajectories as lists of activities and these operators will do (almost) everything you expect. As a side effect, the generics head() and tail() automatically work with trajectories also as expected.
• New length() method to obtain the number of first-level activities in a trajectory (f86375a). Useful in combination with the subsetting operators.

## Minor changes and fixes:

• create_trajectory() has been deprecated in favor of trajectory() (76c1317).
• plot_resource_usage(), plot_resource_utilization(), plot_evolution_arrival_times() and plot_attributes() have been deprecated and will be removed in the next release in order to minimise dependencies (5b43f2b). We plan to release a new package on CRAN covering these features and new ones.
• All methods are now S3 methods, so that a nice intelligible error is displayed if you apply a method to the wrong object (e891045).
• All the activity management -related stuff has been removed, i.e, get_head(), get_tail(), print_activity(), get_next_activity(), get_prev_activity() (f86375a). These methods were only useful for development purposes and nobody should be using them. And it was never a good idea to directly expose external pointers.
• Clone all trajectories before passing them to the C++ core (f655cae).
• Update “Advanced Trajectory Usage” vignette.
• Update “Queueing Systems” vignette.

# simmer 3.5.1

## New features:

• New renege_if() activity triggers reneging upon reception of a signal broadcasted with send() (#84).
• Add support for uninterruptible handlers in trap() (bb2aa46).
• Add support for global attributes in set_attribute() (#82).

## Minor changes and fixes:

• Fix bug in set_queue_size() with queue_size_strict=TRUE: arrivals were not being dropped (#83).
• Fix bug in set_capacity() with a preemptive resource when the old value was Inf: arrivals were not being preempted (63beb2c).
• Fix bug in per-resource activity monitoring: activity was not being reset (55097c9).
• Fix trap() printed information.
• Update “Advanced Trajectory Usage” vignette.
• New “Other SimPy Examples” vignette.

# simmer 3.5.0

## New features:

• set_capacity() and set_queue_size() become activities (#77). Just like seize() and release(), they have the associated set_capacity_selected() and set_queue_size_selected() for a joint use together with select().
• New activate() and deactivate() activities allow an arrival to start or stop a generator, respectively, from inside a trajectory (#80).
• New set_trajectory() and set_distribution() activities allow an arrival to install a new trajectory or distribution, respectively, in a generator from inside a trajectory (#80).
• Refactorised and improved arrival monitoring.
• New interarrival communication activities allowing asynchronous programming: send(), trap(), untrap() and wait() can be used to send signals, wait for signals, trap them and launch asynchronous handlers.
• New log_() activity simply prints messages for debugging purposes (eaa4554).

## Minor changes and fixes:

• Store inline trajectory objects inside the simulation environment to prevent them to be garbage-collected.
• Update “Advanced Trajectory Usage” vignette.

# simmer 3.4.4

## Minor changes and fixes:

• Fix non-defined behaviour caused by a race condition in object destruction under some platforms.

# simmer 3.4.3

## Minor changes and fixes:

• Remove warnings for unused arguments in seize() and seize_selected() (1c8c3bb).
• Fix crash on arrival reneging in non-triggered batches (8713d95).
• Fix crash on batches triggered before the timer expires (8713d95).
• Fix crash on non-released preemptive resources when capacity decreases (#75).
• Leaving without releasing a resource throws a warning (#76).

# simmer 3.4.2

## New features:

• Ongoing (unfinished) arrivals are reported with get_mon_arrivals(ongoing = TRUE) (#73).

## Minor changes and fixes:

• Simplify Rcpp glue: remove unnecessary as<>() calls (ec4e51a).
• Simplify trajectory’s head/tail management (06432a8).
• Now, run(until) runs the simulation exactly until until, instead of until the first event scheduled at a time >= until (e7264f6).
• Fix batch cloning (c20bc1d).
• Coverage improved.

# simmer 3.4.1

## Minor changes and fixes:

• Fix memtest notes on CRAN (heap-use-after-free).
• Fix memory leaks.

# simmer 3.4.0

## New features:

• Prioritization (priority, preemptible, restart) has been moved from seize() to add_generator() (#69). This leads to a more natural interpretation of prioritization values as attributes of arrivals from the same generator, rather than attributes of a seize(). Still, prioritization values can be redefined dynamically from inside a trajectory with the new activity set_prioritization().
• New optional post.seize and reject subtrajectories in seize() and seize_selected() (#49). This feature allows us to fine-tune what happens to an arrival if it cannot seize a resource: instead of getting dropped, it may execute a given subtrajectory.
• New clone() and synchronize() activities (#71). clone() implements the workflow pattern in which an entity is processed in multiple parallel threads. The user can define a different sub-trajectory for each clone. With synchronize(), multiple parallel clones converge and are synchronized: only one continues (the first or the last to arrive), and the others are removed.
• New batch() and separate() activities (#45). They can be used to implement a rollercoaster process: batch() collects a number of arrivals before they can continue processing as a block, and separate() splits a previously established batch.
• New renege_in() and renege_abort() activities (#58). They can be used to set or unset a timer after which the arrival will abandon.

## Minor changes and fixes:

• If a branch()’s option returns 0, the arrival skips the branch() and continues to the next activity instead of throwing an index out of range error (#70).
• Throw errors on incorrect releases (#72).
• Remove deprecated convenience function every() (#65) and branch()’s deprecated argument merge (#57).
• New “The Bank Tutorial: Part I” vignette, by Duncan Garmonsway @nacnudus (#68).
• Update “Advanced Trajectory Usage” vignette.

# simmer 3.3.0

## New features:

• New join() activity to concatenate trajectories (#50).
• Batched generation: the generation function can return more than one interarrival value at a time (#65).
• Add the option queue_size_strict to add_resource() to guarantee the queue size limit with preemption (#59).
• New select(), seize_selected() and release_selected() activities (#52).
• Modify resources (capacity, queue size) from inside a trajectory (#66).
• New leave() activity (#63).

## Major fixes:

• Fix per-resource activity time monitoring (#67). The problem emerged when an arrival revisited a resource and it was enqueued. An uninitialised variable could lead to an activity time greater than end_time - start_time. All versions 3.2.x are affected by this bug.

## Minor changes and fixes:

• Fix the description of preemptible in the documentation of seize() and force preemptible to be equal or greater than priority (#53).
• Reset finite generators (#51).
• Fix the handling of a capacity change when the new value is infinite (#60).
• Various doc fixes (#61).
• Change branch()’s merge parameter name to continue. The old name is deprecated (#57).
• Use match.arg() in multiple-choice arguments (#55).
• Fix branch() backwards linking and count (#56).
• Split release() in two steps to deal properly with capacity changes at the same point in time (#64).
• The convenience function every() is deprecated due to #65.
• Update and extend previous vignettes.

# simmer 3.2.1

## New features:

• Add time-specific resource availability support (#21). Both resources’ capacity and queue_size can change over time following a user-defined scheduling, which can be generated with the new function schedule().
• Advanced peek: inspect any number of future events in the event queue (8147820). For more details, see ?peek.

## Minor changes and fixes:

• Fix steps grouping in plot_resource_usage() (8da9b97).
• Fix incorrect trajectory behaviour when a rejection occurs inside a branch with merge=TRUE (#46).
• Fix a couple of segmentation faults in preemptive resources (f64f6b2).
• Improve verbose output (9013db0).
• New multiset-based event queue with unscheduling capabilities (a615fea and d6a9d67).
• A simulation may run forever (until the user interrupts it), that is, until=Inf is allowed now (f47baa9).
• New vignette on queueing systems.
• New vignette on Continuous-Time Markov Chains.
• Update and extend previous vignettes.

# simmer 3.2.0

## Major fix:

• In previous versions, resources were monitored before performing the corresponding seize/release activity, before changing the status of the system. Thus, t=3, queue=2 meant that, until t=3, the queue had 2 customers, and at t=3 the system changed (because of a new arrival or a new departure). The idea was to keep the values and time vectors aligned (see #28). But from this moment on, the resources are monitored __after_ changing the status of the system. This is more consistent with what a user would expect, and more consistent with the behaviour of other related R functions (e.g., see stepfun(), from the stats package). Wrapping up and from now on, t=3, queue=2 means that some event happened at t=3 whose immediate and subsequent result was a queue with 2 customers.

## New features:

• Add preemption functionality (#34). Preemption comes into play when a resource is specified as preemptive=TRUE. Arrivals in the server can be preempted on a preempt_order="fifo" or preempt_order="lifo" basis. Each seize() has three basic properties:
• priority: already present in previous versions.
• preemptible: another seize() with a priority value greater than this may preempt the present seize().
• restart: whether the current task (a timeout() activity, for instance) should be restarted if the arrival is preempted.

## Minor changes and fixes:

• Remove deprecated functions show_activity() and show_trajectory().
• Add every(), to() and from_to() convenience functions (8e524cd).
• Fix colour scale in plot_resource_usage() (6b034a7).
• Fix compatibility with the upcoming version of testthat (#41).
• The branch() activity now provides attributes to its option function, as the other activities (#42).
• Implement error handling in plot_*() functions (#44).

# simmer 3.1.2

## New features:

• Monitor arrivals’ start/activity/end times on a per-resource basis (#38). So far, the function get_mon_arrivals() returned the start/activity/end times per arrival for the whole trajectory. This behaviour remains, but additionally, get_mon_arrivals(per_resource = TRUE) returns these times per resource, so that it is possible to retrieve queueing/system times per resource.

## Minor changes and fixes:

• Fix testing ERRORs reported on platforms using clang and Sparc Solaris.
• get_mon_*() functions accept a single simulation environment as well as a list of environments representing several replications (5ee2725). A new column (replication) in the resulting data frame indicates the corresponding replication number.
• Monitoring subsystem refactored (as a consequence of #38).

# simmer 3.1.1

## New features:

• Add attributes to arrivals and new set_attribute() activity (#16).
• New rollback() activity (#17 and #22).
• Add priorities to resources’ queue (#20).

## Minor changes and fixes:

• Performance improvements with Boost (1b654fd).
• Fix arrivals’ timing issues (#24).
• Nicer object printing (#26).
• Return self visibly, instead of invisibly (#35).
• Add at() and from() convenience functions (29cccd2 and 7cfdd90).
• Some work on vignettes (#29).
• Fix ggplot2 2.0.0 compatibility issues (#37).

# simmer 3.0.1

## Minor changes and fixes:

• Complete test coverage (#12).
• Minor fix in the documentation (42363d2).
• Set finalizer in the simulator object (#14).
• Fix test errors under Windows r-oldrelease (#15).

# simmer 3.0.0

## New features:

• First major release submitted to CRAN. The philosophy and workflow of the pre-release remain with a more robust event-based C++ backend and a more flexible frontend.
• Enhanced programmability. The timeout activity is more than just a delay. It admits a user-defined function, which can be as complex as needed in order to interact with the simulation model. The old v2.0 was no more than a queueing network simulator. This feature makes simmer a flexible and generic DES framework. Moreover, we have finally got rid of the infamous add_skip_event() function to implement a more flexible and user-friendly branching method.
• Robustness. The event-based core design is rigorous and simple, which makes simmer faster and less error-prone, at the same level of other state-of-the-art DES frameworks.
• Much better performance. Instead of creating n arrivals beforehand, this release leverages the concept of generator of arrivals, which is faster and more flexible. At the same time, the concept of trajectory as a chain of activities is implemented entirely in C++ internally. Our tests show that simmer is even faster than SimPy when it comes to simulate queueing networks.
• Replication. In the pre-release, replication was implemented inside simmer. This no longer makes sense since, with the current design, it is more than straightforward to replicate and even parallelize the execution of replicas using standard R tools.