Effects Counter#

An FFI example demonstrating future_form's sans-IO effect protocol. A counter service requests capabilities from the host (timestamps, logging) rather than performing I/O directly. Foreign hosts (Go, Java, Python) inspect pending effects, fulfill them, and re-poll.

What this demonstrates#

The sans-IO effect protocol (EffectSlot + EffectHandle)
Host-fulfilled effects: GetTimestamp and Log
Per-struct EffectSlot (one future at a time)
The same async state machine driven by Go, Java, and Python hosts

Structure#

counter_effects/
├── counter_effects/  Domain logic: EffectCounter with GetTimestamp + Log effects
├── effects_bridge/   C ABI + JNI bridge (effects counter)
├── go_host/          Go host with effect fulfillment
├── java_host/        Java host with effect fulfillment
├── python_host/      Python host with effect fulfillment
└── run_test.sh       Build + run across all hosts

Running#

From the workspace root, using nix develop .#ffi for foreign toolchains:

./future_form_ffi/examples/counter_effects/run_test.sh

Prerequisites#

See counter_simple for the basic polling pattern without effects. For concurrent per-future effect slots, see the key_value_store example.

Limitations#

This example uses a per-struct EffectSlot -- only one future can be in flight at a time per counter instance. For concurrent futures, see the key_value_store example which uses per-future Arc<EffectSlot>.

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