Running Simulations

Drive Modes

Oakfield contexts can be driven in three common ways:

• Call step(ctx) yourself in a script-controlled loop.
• Call run(ctx, [config]) and let the scheduler own the loop.
• Claim external-driver ownership and cooperate with host or embedder control APIs.

Script-controlled Stepping

When running simulations from the command line, you will usually own the loop directly:

local ctx = ooc.create({ worker_count = 1 })

-- add fields/operators...

local integrator = ooc.create_context_integrator(ctx, "rkf45", {
    initial_dt = 0.01,
    adaptive = true,
})

ooc.set_integrator(ctx, integrator)

for step = 1, 10000 do
    if not ooc.step(ctx) then
        ooc.log(ooc.LOG_LEVEL_ERROR, "step %d failed", step)
        break
    end

    if step % 100 == 0 then
        local m = ooc.step_metrics_latest(ctx)
        if m then
            ooc.log("t=%.3f dt=%.4f rms=%.2e",
                ooc.get_time(ctx), m.accepted_dt, m.rms_error)
        end
    end
end

ooc.shutdown(ctx)

Note: How step Executes

step(ctx) always advances exactly one accepted step, but the runtime may choose either:

• a scheduler-backed single-step path, or
• the legacy single-threaded path

The scheduler path is typically chosen when multi-worker execution is requested, an integrator is attached, and no Lua operator callbacks force a fallback.

Scheduler Ownership

These helpers start and control the long-running scheduler loop:

run(ctx, [config])
pause(ctx)
resume(ctx)
shutdown(ctx)
is_running(ctx) -> boolean

run(ctx, [config]) reuses the context’s stored config and optionally patches it with the same recognized keys as create, such as worker_count, enable_logging, enable_profiling, enable_timestep_heuristics, frame_time_budget_ms, backend, backend_fallback, and log_path.

ooc.run(ctx, {
    worker_count = 4,
    enable_logging = true,
    log_path = "logs/scheduler.log",
})

Use pause / resume only when the scheduler currently owns the loop. shutdown stops the context and releases runtime resources.

Driver State Snapshot

For host integration and debugging, use:

driver_state(ctx) -> state|nil

The returned table includes:

• active_mode and owner for the current driver arrangement
• scheduler_state, running, and paused
• scheduler_initialized
• integrator_attached and integrator_sequence_count
• step_metrics_available and step_metrics_count
• external_driver_depth
• inspect_allowed, export_allowed, and mutation_allowed
• caller_loop_control_allowed and scheduler_control_allowed
• access_reason
• loop_progress when a bounded or cooperative loop is active

Minimal example:

local state = ooc.driver_state(ctx)
if state then
    ooc.log("owner=%s running=%s paused=%s",
        state.owner, tostring(state.running), tostring(state.paused))
end

External Driver Control

Embedders can explicitly claim loop ownership:

begin_external_driver(ctx) -> depth
end_external_driver(ctx) -> depth
with_external_driver(ctx, fn) -> ...

with_external_driver is the safest pattern. It acquires ownership, calls fn(ctx), then releases ownership even if you nest driver scopes elsewhere.

ooc.with_external_driver(ctx, function(context)
    for i = 1, 128 do
        if not ooc.step(context) then
            break
        end
    end
end)

Cooperative Loop Helpers

These APIs help external drivers coordinate cancellation, pause, and bounded sleeps:

loop_checkpoint(ctx) -> checkpoint
request_loop_stop(ctx) -> checkpoint
clear_loop_stop(ctx) -> checkpoint
loop_cooperate(ctx, [opts]) -> checkpoint

The checkpoint table includes:

• step_index
• sim_time
• pending_cancel
• should_stop
• last_stop_reason
• has_error
• last_error
• progress
• driver

loop_cooperate(ctx, { sleep_seconds = x }) clamps the cooperative sleep request into the runtime’s safe range before sleeping, then returns the same checkpoint table plus:

• sleep_requested_seconds
• sleep_seconds
• sleep_applied
• sleep_clamped

Example:

ooc.with_external_driver(ctx, function(context)
    while true do
        if not ooc.step(context) then
            break
        end

        local cp = ooc.loop_cooperate(context, { sleep_seconds = 0.01 })
        if cp.should_stop then
            break
        end
    end
end)

Scheduler Logs

scheduler_drain_logs(ctx, [min_level], [callback]) -> boolean

Accepted call patterns:

• scheduler_drain_logs(ctx) drains and discards all pending records
• scheduler_drain_logs(ctx, "warn") drains only warn and above
• scheduler_drain_logs(ctx, function(level, message) ... end) drains and invokes the callback
• scheduler_drain_logs(ctx, "info", function(level, message) ... end) combines filtering and callbacks

This only produces records when scheduler logging is enabled.

GUI / Host-returned Contexts

In GUI or embedder scripts, the common pattern is to build a context and return it:

local ctx = ooc.create()
ooc.set_timestep(ctx, 0.025)

local field = ooc.add_field(ctx, {512}, {
    type = "complex_double",
    fill = {0.0, 0.0},
})

ooc.add_zero_field_operator(ctx, field)
ooc.set_integrator(ctx, ooc.create_context_integrator(ctx, "euler"))

return ctx

The host can then inspect driver_state, claim external ownership, or run the scheduler around that returned context.

Applying Snapshots

apply_snapshot(ctx, snapshot_table) -> applied_count

Each snapshot entry must include:

• name
• schema
• blob as a hex string

Optional fields:

• index as an operator index hint
• size as the expected decoded blob size

Entries that do not decode cleanly are skipped. If the native snapshot apply fails, the binding raises a Lua error and reports how many overrides were already applied.

local applied = ooc.apply_snapshot(ctx, {
    {
        name = "stimulus_sine#0",
        schema = "stimulus_sine",
        blob = "<hex...>",
    }
})

ooc.log("applied %d snapshot entries", applied)