State and Concurrency on FsFlow

Ref (Atomic References)

Mon, 01 Jan 0001 00:00:00 +0000

Ref (Atomic References)

Ref<'T> is a handle to a mutable reference that can be updated atomically. It is the simplest way to manage shared state between multiple concurrent parts of your application.

Note: Ref is currently available on .NET only.

Why Use Ref?

In a functional program, state is usually passed as parameters or through the environment. However, some scenarios—like a shared counter, a cache, or a status flag—require multiple concurrent workflows to observe and update the same value.

Schedule (Retry & Repeat)

Mon, 01 Jan 0001 00:00:00 +0000

Schedule (Retry & Repeat)

The Schedule module provides a powerful DSL for describing policies that govern how and when a workflow should be executed again. You can use schedules to implement sophisticated retry strategies (like exponential backoff with jitter) or recurring tasks.

Note: Schedule is currently available on .NET only.

Basic Schedules

A schedule decides two things:

Whether to continue (recur).
How long to wait before the next attempt.

Fixed Number of Recursions

// Recur 5 times (6 attempts total)
let fiveTimes = Schedule.recurs 5

Fixed Spacing

// Recur indefinitely with 1 second between attempts
let everySecond = Schedule.spaced (TimeSpan.FromSeconds 1.0)

Exponential Backoff

// Delays: 100ms, 200ms, 400ms, 800ms...
let backoff = Schedule.exponential (TimeSpan.FromMilliseconds 100.0)

Adding Jitter

Jitter adds randomness to delays to prevent “thundering herd” problems in distributed systems. Schedule.jittered adds a random factor between 0.5x and 1.5x to the current delay.

STM (Software Transactional Memory)

Mon, 01 Jan 0001 00:00:00 +0000

STM (Software Transactional Memory)

Software Transactional Memory (STM) is a powerful concurrency primitive that allows you to combine multiple atomic operations into a single transaction.

While Ref is perfect for updating a single variable, STM is designed for scenarios where you need to update multiple variables consistently. FsFlow ensures that the entire transaction is executed atomically—either all changes are committed, or none are.

Note: STM is currently available on .NET only.

Stream (FlowStream)

Mon, 01 Jan 0001 00:00:00 +0000

Stream (FlowStream)

FlowStream<'env, 'error, 'value> represents a cold, pull-based asynchronous stream. Like Flow, a FlowStream requires an environment to run and can fail with a typed error. It is built on top of .NET’s IAsyncEnumerable, providing native support for backpressure and asynchronous iteration.

Note: FlowStream is currently available on .NET only.

Creating a Stream

From a Sequence

The simplest way to create a stream is from an existing seq.

let numbers = FlowStream.fromSeq [ 1 .. 10 ]

Transforming Streams

Mapping Values

You can transform the successful values in a stream using FlowStream.map.