cadence.go

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/*
Package cadence and its subdirectories contain the Cadence client side framework.

The Cadence service is a task orchestrator for your application’s tasks. Applications using Cadence can execute a
logical flow of tasks, especially long-running business logic, asynchronously or synchronously. They can also scale at
runtime on distributed systems.

A quick example illustrates its use case. Consider Uber Eats where Cadence manages the entire business flow from
placing an order, accepting it, handling shopping cart processes (adding, updating, and calculating cart items),
entering the order in a pipeline (for preparing food and coordinating delivery), to scheduling delivery as well as
handling payments.

Cadence consists of a programming framework (or client library) and a managed service (or backend). The framework
enables developers to author and coordinate tasks in Go code.

The root cadence package contains common data structures. The subpackages are:

  - workflow - functions used to implement workflows
  - activity - functions used to implement activities
  - client - functions used to create Cadence service client used to start and
    monitor workflow executions.
  - worker - functions used to create worker instance used to host workflow and
    activity code.
  - testsuite - unit testing framework for activity and workflow testing

# How Cadence works

The Cadence hosted service brokers and persists events generated during workflow execution. Worker nodes owned and
operated by customers execute the coordination and task logic. To facilitate the implementation of worker nodes Cadence
provides a client-side library for the Go language.

In Cadence, you can code the logical flow of events separately as a workflow and code business logic as activities. The
workflow identifies the activities and sequences them, while an activity executes the logic.

# Key Features

Dynamic workflow execution graphs - Determine the workflow execution graphs at runtime based on the data you are
processing. Cadence does not pre-compute the execution graphs at compile time or at workflow start time. Therefore, you
have the ability to write workflows that can dynamically adjust to the amount of data they are processing. If you need
to trigger 10 instances of an activity to efficiently process all the data in one run, but only 3 for a subsequent run,
you can do that.

Child Workflows - Orchestrate the execution of a workflow from within another workflow. Cadence will return the results
of the child workflow execution to the parent workflow upon completion of the child workflow. No polling is required in
the parent workflow to monitor status of the child workflow, making the process efficient and fault tolerant.

Durable Timers - Implement delayed execution of tasks in your workflows that are robust to worker failures. Cadence
provides two easy to use APIs, **workflow.Sleep** and **workflow.Timer**, for implementing time based events in your
workflows. Cadence ensures that the timer settings are persisted and the events are generated even if workers executing
the workflow crash.

Signals - Modify/influence the execution path of a running workflow by pushing additional data directly to the workflow
using a signal. Via the Signal facility, Cadence provides a mechanism to consume external events directly in workflow
code.

Task routing - Efficiently process large amounts of data using a Cadence workflow, by caching the data locally on a
worker and executing all activities meant to process that data on that same worker. Cadence enables you to choose the
worker you want to execute a certain activity by scheduling that activity execution in the worker's specific task-list.

Unique workflow ID enforcement - Use business entity IDs for your workflows and let Cadence ensure that only one
workflow is running for a particular entity at a time. Cadence implements an atomic "uniqueness check" and ensures that
no race conditions are possible that would result in multiple workflow executions for the same workflow ID. Therefore,
you can implement your code to attempt to start a workflow without checking if the ID is already in use, even in the
cases where only one active execution per workflow ID is desired.

Perpetual/ContinueAsNew workflows - Run periodic tasks as a single perpetually running workflow. With the
"ContinueAsNew" facility, Cadence allows you to leverage the "unique workflow ID enforcement" feature for periodic
workflows. Cadence will complete the current execution and start the new execution atomically, ensuring you get to
keep your workflow ID. By starting a new execution Cadence also ensures that workflow execution history does not grow
indefinitely for perpetual workflows.

At-most once activity execution - Execute non-idempotent activities as part of your workflows. Cadence will not
automatically retry activities on failure. For every activity execution Cadence will return a success result, a failure
result, or a timeout to the workflow code and let the workflow code determine how each one of those result types should
be handled.

Asynch Activity Completion - Incorporate human input or thrid-party service asynchronous callbacks into your workflows.
Cadence allows a workflow to pause execution on an activity and wait for an external actor to resume it with a
callback. During this pause the activity does not have any actively executing code, such as a polling loop, and is
merely an entry in the Cadence datastore. Therefore, the workflow is unaffected by any worker failures happening over
the duration of the pause.

Activity Heartbeating - Detect unexpected failures/crashes and track progress in long running activities early. By
configuring your activity to report progress periodically to the Cadence server, you can detect a crash that occurs 10
minutes into an hour-long activity execution much sooner, instead of waiting for the 60-minute execution timeout. The
recorded progress before the crash gives you sufficient information to determine whether to restart the activity from
the beginning or resume it from the point of failure.

Timeouts for activities and workflow executions - Protect against stuck and unresponsive activities and workflows with
appropriate timeout values. Cadence requires that timeout values are provided for every activity or workflow
invocation. There is no upper bound on the timeout values, so you can set timeouts that span days, weeks, or even
months.

Visibility - Get a list of all your active and/or completed workflow. Explore the execution history of a particular
workflow execution. Cadence provides a set of visibility APIs that allow you, the workflow owner, to monitor past and
current workflow executions.

Debuggability - Replay any workflow execution history locally under a debugger. The Cadence client library provides an
API to allow you to capture a stack trace from any failed workflow execution history.
*/
package cadence

import "go.uber.org/cadence/internal"

// RetryPolicy defines the retry policy for activity/workflow.
type RetryPolicy = internal.RetryPolicy