Scheduling callbacks and output writers

Callbacks and output writers in Simulation actuate on objects that subtype Oceananigans.Utils.AbstractSchedule. Schedules are small callable objects that return true when an action should fire and false otherwise. This page collects the built-in schedules, when to use them, and how to combine them for more complex behavior.

For the following examples, we will use the following simple simulation and progress:

using Oceananigans
grid = RectilinearGrid(size=(1, 1, 1), extent=(1, 1, 1))
model = NonhydrostaticModel(; grid)
simulation = Simulation(model, Δt=0.1, stop_time=2.5, verbose=false)
dummy(sim) = @info string("Iter: ", iteration(sim), " -- I was called at t = ", time(sim),
                          " and wall time = ", prettytime(sim.run_wall_time))

dummy (generic function with 1 method)

IterationInterval

IterationInterval(interval) actuates every interval iterations:

schedule = IterationInterval(11)
add_callback!(simulation, dummy, schedule, name=:dummy)
run!(simulation)

[ Info: Iter: 0 -- I was called at t = 0.0 and wall time = 0 seconds
[ Info: Iter: 11 -- I was called at t = 1.0999999999999999 and wall time = 43.145 ms
[ Info: Iter: 22 -- I was called at t = 2.2000000000000006 and wall time = 47.268 ms

Use the offset kwarg to shift the trigger so that, for example,

Oceananigans.Simulations.reset!(simulation)
simulation.stop_time = 2.5

schedule = IterationInterval(7; offset=-2)
add_callback!(simulation, dummy, schedule, name=:dummy)
run!(simulation)

[ Info: Iter: 0 -- I was called at t = 0.0 and wall time = 0 seconds
[ Info: Iter: 5 -- I was called at t = 0.5 and wall time = 1.869 ms
[ Info: Iter: 12 -- I was called at t = 1.2 and wall time = 64.304 ms
[ Info: Iter: 19 -- I was called at t = 1.9000000000000006 and wall time = 67.346 ms

notice that the callback is actuated on iterations 5, 12, 19, …

Above, we have overwritten the original callback called "dummy" with the new one with the offset schedule. An alternative way is to construct the Callback manually and add it in the simulation:

simulation.callbacks[:dummy] = Callback(dummy, schedule)

Callback of dummy on IterationInterval(7) with offset -2

TimeInterval

TimeInterval(interval) actuates every interval of model time, in units corresponding to model.clock.time. For example,

Oceananigans.Simulations.reset!(simulation)
simulation.stop_time = 2.5

schedule = TimeInterval(1.11)
add_callback!(simulation, dummy, schedule, name=:dummy)
run!(simulation)

[ Info: Iter: 0 -- I was called at t = 0.0 and wall time = 0 seconds
[ Info: Iter: 12 -- I was called at t = 1.11 and wall time = 26.625 ms
[ Info: Iter: 24 -- I was called at t = 2.22 and wall time = 31.040 ms

When model.clock.time isa AbstractTime such as DateTime, then interval can be Dates.Period:

using Dates

start_time = DateTime(2025, 1, 1)
clock = Clock(time = start_time)
datetime_model = NonhydrostaticModel(; grid, clock)

stop_time = start_time + Dates.Minute(3)
datetime_simulation = Simulation(datetime_model; Δt=Dates.Second(25), stop_time, verbose=false)

schedule = TimeInterval(Dates.Minute(1))
add_callback!(datetime_simulation, dummy, schedule)
run!(datetime_simulation)

[ Info: Iter: 0 -- I was called at t = 2025-01-01T00:00:00 and wall time = 0 seconds
[ Info: Iter: 3 -- I was called at t = 2025-01-01T00:01:00 and wall time = 885.222 ms
[ Info: Iter: 6 -- I was called at t = 2025-01-01T00:02:00 and wall time = 886.597 ms
[ Info: Iter: 9 -- I was called at t = 2025-01-01T00:03:00 and wall time = 887.796 ms

WallTimeInterval

WallTimeInterval(interval; start_time=time_ns()*1e-9) uses wall-clock seconds instead of model time. This is mostly useful for writing checkpoints to disk after consuming a fixed amount of computational resources. For example, using the previous simulation without the

Oceananigans.Simulations.reset!(simulation)
simulation.stop_time = 2.5

schedule = WallTimeInterval(0.005)
add_callback!(simulation, dummy, schedule, name=:dummy)
run!(simulation)

[ Info: Iter: 0 -- I was called at t = 0.0 and wall time = 0 seconds
[ Info: Iter: 1 -- I was called at t = 0.1 and wall time = 0 seconds
[ Info: Iter: 3 -- I was called at t = 0.30000000000000004 and wall time = 21.313 ms
[ Info: Iter: 15 -- I was called at t = 1.5000000000000002 and wall time = 26.029 ms

SpecifiedTimes

SpecifiedTimes(times...) actuates when model.clock.time reaches the given values. The constructor accepts numeric times or Dates.DateTime values and sorts them automatically. This schedule is helpful for pre-planned save points or events tied to specific model times.

Oceananigans.Simulations.reset!(simulation)
simulation.stop_time = 2.5

schedule = SpecifiedTimes(0.2, 1.5, 2.1)
add_callback!(simulation, dummy, schedule, name=:dummy)
run!(simulation)

[ Info: Iter: 0 -- I was called at t = 0.0 and wall time = 0 seconds
[ Info: Iter: 2 -- I was called at t = 0.2 and wall time = 23.292 ms
[ Info: Iter: 15 -- I was called at t = 1.5 and wall time = 71.846 ms
[ Info: Iter: 21 -- I was called at t = 2.1 and wall time = 74.179 ms

Arbitrary functions of model

Any function of model that returns a Bool can be used as a schedule:

Oceananigans.Simulations.reset!(simulation)
simulation.stop_time = 2.5

after_two(model) = model.clock.time > 2
add_callback!(simulation, dummy, after_two, name=:dummy)
run!(simulation)

[ Info: Iter: 0 -- I was called at t = 0.0 and wall time = 0 seconds
[ Info: Iter: 20 -- I was called at t = 2.0000000000000004 and wall time = 20.717 ms
[ Info: Iter: 21 -- I was called at t = 2.1000000000000005 and wall time = 21.174 ms
[ Info: Iter: 22 -- I was called at t = 2.2000000000000006 and wall time = 21.600 ms
[ Info: Iter: 23 -- I was called at t = 2.3000000000000007 and wall time = 22.006 ms
[ Info: Iter: 24 -- I was called at t = 2.400000000000001 and wall time = 22.397 ms
[ Info: Iter: 25 -- I was called at t = 2.5 and wall time = 22.792 ms

Combining schedules

Some applications benefit from running extra steps immediately after an event or from combining multiple criteria.

ConsecutiveIterations

ConsecutiveIterations(parent_schedule, N=1) actuates when the parent schedule does and for the next N iterations. For example, averaging callbacks often need data at the scheduled time and immediately afterwards.

Oceananigans.Simulations.reset!(simulation)
simulation.stop_time = 2.5

times = SpecifiedTimes(0.55, 1.5, 2.12)
schedule = ConsecutiveIterations(times)
add_callback!(simulation, dummy, schedule, name=:dummy)
run!(simulation)

[ Info: Iter: 0 -- I was called at t = 0.0 and wall time = 0 seconds
[ Info: Iter: 1 -- I was called at t = 0.1 and wall time = 0 seconds
[ Info: Iter: 6 -- I was called at t = 0.55 and wall time = 23.984 ms
[ Info: Iter: 7 -- I was called at t = 0.65 and wall time = 29.725 ms
[ Info: Iter: 16 -- I was called at t = 1.5 and wall time = 36.680 ms
[ Info: Iter: 17 -- I was called at t = 1.6 and wall time = 37.491 ms
[ Info: Iter: 23 -- I was called at t = 2.12 and wall time = 64.288 ms
[ Info: Iter: 24 -- I was called at t = 2.22 and wall time = 64.766 ms

AndSchedule and OrSchedule

Use AndSchedule(s₁, s₂, ...) when an action should fire only if every child schedule actuates in the same iteration. Use OrSchedule(s₁, s₂, ...) when any one of the child schedules should trigger the action. Both accept any mix of AbstractSchedules, so you can require, for example, output every hour and every 1000 iterations:

Oceananigans.Simulations.reset!(simulation)
simulation.stop_time = 2.5

after_one_point_seven(model) = model.clock.time > 1.7
schedule = AndSchedule(IterationInterval(2), after_one_point_seven)
add_callback!(simulation, dummy, schedule, name=:dummy)
run!(simulation)

[ Info: Iter: 0 -- I was called at t = 0.0 and wall time = 0 seconds
[ Info: Iter: 18 -- I was called at t = 1.8000000000000005 and wall time = 42.661 ms
[ Info: Iter: 20 -- I was called at t = 2.0000000000000004 and wall time = 43.524 ms
[ Info: Iter: 22 -- I was called at t = 2.2000000000000006 and wall time = 44.319 ms
[ Info: Iter: 24 -- I was called at t = 2.400000000000001 and wall time = 45.115 ms

Stateful schedules such as TimeInterval, SpecifiedTimes, and ConsecutiveIterations store their own counters, so create a fresh instance (or call copy) for each callback or output writer that needs an identical pattern.

Output-specific schedules

Some schedules only apply to output writers because they keep extra state or require file access.

AveragedTimeInterval

AveragedTimeInterval(interval; window=interval, stride=1) asks an output writer to accumulate data over a sliding time window before writing. The window ends at each actuation time, runs for window seconds, and samples every stride iterations inside the window.

AveragedSpecifiedTimes

AveragedSpecifiedTimes(times; window, stride=1) behaves like SpecifiedTimes but with a trailing averaging window. Pass either a SpecifiedTimes instance or raw times.

FileSizeLimit

FileSizeLimit(size_limit) actuates when the target file grows beyond size_limit bytes. Output writers update the internal path automatically so you usually only pass the size limit. Combine it with OrSchedule to rotate files when either the clock reaches a value or the file becomes too large.