Atomic Blocks and Durability Controls (MoonBit)

Overview

Golem provides automatic durable execution — all agents are durable by default. These APIs are advanced controls that most agents will never need. Only use them when you have specific requirements around persistence granularity, idempotency, or atomicity.

The high-level APIs are in the @api package (golemcloud/golem_sdk/api). Import it with an alias like @api. The types PersistenceLevel and RetryPolicy are re-exported from this package.

Atomic Operations

Group side effects so they are retried together on failure. Use with_atomic_operation for automatic lifecycle management:

fn atomic_transfer(from : Account, to : Account, amount : Double) -> Unit {
  @api.with_atomic_operation(fn() {
    let withdrawn = from.withdraw(amount)
    to.deposit(withdrawn)
  })
}

If the agent fails mid-block, the entire block is re-executed on recovery rather than resuming from the middle.

For manual control, use mark_begin_operation / mark_end_operation:

fn atomic_transfer(from : Account, to : Account, amount : Double) -> Unit {
  let begin = @api.mark_begin_operation()
  let withdrawn = from.withdraw(amount)
  to.deposit(withdrawn)
  @api.mark_end_operation(begin)
}

Persistence Level Control

Temporarily adjust oplog recording for performance-sensitive sections. Use with_persistence_level for automatic save/restore:

fn do_fast_work() -> Unit {
  @api.with_persistence_level(@api.PersistenceLevel::PersistNothing, fn() {
    // Side effects here will be replayed on recovery instead of persisted
    do_idempotent_work()
  })
}

For manual control, use get_oplog_persistence_level / set_oplog_persistence_level:

let original = @api.get_oplog_persistence_level()
@api.set_oplog_persistence_level(@api.PersistenceLevel::PersistNothing)
do_idempotent_work()
@api.set_oplog_persistence_level(original)

PersistenceLevel Variants

Idempotence Mode

Control whether HTTP requests are retried when the result is uncertain. Use with_idempotence_mode for scoped control:

fn make_payment(amount : Double) -> String {
  @api.with_idempotence_mode(false, fn() {
    // At-most-once semantics for this non-idempotent call
    charge_payment(amount)
  })
}

For manual control:

@api.set_idempotence_mode(false)
let result = charge_payment(amount)
@api.set_idempotence_mode(true)

Use @api.get_idempotence_mode() to read the current setting.

Oplog Commit

Wait until the oplog is replicated to a specified number of replicas before continuing:

// Ensure oplog is replicated to 3 replicas before proceeding
@api.oplog_commit(b'\x03')

The argument is the desired replica count (Byte type).

Idempotency Key Generation

Generate a durable idempotency key that persists across agent restarts — safe for payment APIs and other exactly-once operations:

let key = @api.generate_idempotency_key()
// key is a @types.Uuid — use it with external APIs for exactly-once processing

// Or get it as a string directly:
let key_str = @api.generate_idempotency_key_string()

Retry Policy

Override the default retry policy for a block of code. Use with_retry_policy for scoped control:

fn do_flaky_work() -> Unit {
  @api.with_retry_policy(
    @api.RetryPolicy::{
      max_attempts: 5U,
      min_delay: 100UL,         // milliseconds
      max_delay: 5000UL,        // milliseconds
      multiplier: 2.0,
      max_jitter_factor: Some(0.1),
    },
    fn() { do_flaky_operation() },
  )
}

For manual control, use get_retry_policy / set_retry_policy:

let original = @api.get_retry_policy()
@api.set_retry_policy(@api.RetryPolicy::{
  max_attempts: 5U,
  min_delay: 100UL,
  max_delay: 5000UL,
  multiplier: 2.0,
  max_jitter_factor: Some(0.1),
})
do_flaky_operation()
@api.set_retry_policy(original)

Import Path

Add the api package to your moon.pkg imports:

import {
  "golemcloud/golem_sdk/api" @api,
}

All durability, persistence, idempotency, retry, and oplog APIs are available from @api.

Low-Level Durability API

For advanced use cases (e.g., manually persisting function invocations for replay), the raw durability APIs are available in golemcloud/golem_sdk/interface/golem/durability/durability:

• begin_durable_function(function_type) / end_durable_function(function_type, begin_index, forced_commit)
• current_durable_execution_state() — returns DurableExecutionState { is_live, persistence_level }
• persist_durable_function_invocation(function_name, request, response, function_type)
• read_persisted_durable_function_invocation()

These are rarely needed — prefer the @api wrappers above.