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Temporal .NET SDK

NuGet MIT

Temporal is a distributed, scalable, durable, and highly available orchestration engine used to execute asynchronous, long-running business logic in a scalable and resilient way.

"Temporal .NET SDK" is the framework for authoring workflows and activities using .NET programming languages.

Also see:

Extensions:

Contents

Quick Start

Installation

Add the Temporalio package from NuGet. For example, using the dotnet CLI:

dotnet add package Temporalio

If you are using .NET Framework or a non-standard target platform, see the Built-in Native Shared Library section later for additional information.

NOTE: This README is for the current branch and not necessarily what's released on NuGet.

Implementing a Workflow and Activity

Assuming the ImplicitUsings is enabled, create an activity by putting the following in MyActivities.cs:

namespace MyNamespace;

using Temporalio.Activities;

public class MyActivities
{
    // Activities can be async and/or static too! We just demonstrate instance
    // methods since many will use them that way.
    [Activity]
    public string SayHello(string name) => $"Hello, {name}!";
}

That creates the activity. Now to create the workflow, put the following in SayHelloWorkflow.workflow.cs:

namespace MyNamespace;

using Temporalio.Workflows;

[Workflow]
public class SayHelloWorkflow
{
    [WorkflowRun]
    public async Task<string> RunAsync(string name)
    {
        // This workflow just runs a simple activity to completion.
        // StartActivityAsync could be used to just start and there are many
        // other things that you can do inside a workflow.
        return await Workflow.ExecuteActivityAsync(
            // This is a lambda expression where the instance is typed. If this
            // were static, you wouldn't need a parameter.
            (MyActivities act) => act.SayHello(name),
            new() { ScheduleToCloseTimeout = TimeSpan.FromMinutes(5) });
    }
}

This is a simple workflow that executes the SayHello activity.

Running a Worker

To run this in a worker, put the following in Program.cs:

using MyNamespace;
using Temporalio.Client;
using Temporalio.Worker;

// Create a client to localhost on "default" namespace
var client = await TemporalClient.ConnectAsync(new("localhost:7233"));

// Cancellation token to shutdown worker on ctrl+c
using var tokenSource = new CancellationTokenSource();
Console.CancelKeyPress += (_, eventArgs) =>
{
    tokenSource.Cancel();
    eventArgs.Cancel = true;
};

// Create an activity instance since we have instance activities. If we had
// all static activities, we could just reference those directly.
var activities = new MyActivities();

// Create worker with the activity and workflow registered
using var worker = new TemporalWorker(
    client,
    new TemporalWorkerOptions("my-task-queue").
        AddActivity(activities.SayHello).
        AddWorkflow<SayHelloWorkflow>());

// Run worker until cancelled
Console.WriteLine("Running worker");
try
{
    await worker.ExecuteAsync(tokenSource.Token);
}
catch (OperationCanceledException)
{
    Console.WriteLine("Worker cancelled");
}

When executed, this will listen for Temporal server requests to perform workflow and activity invocations.

Executing a Workflow

To start and wait on a workflow result, with the worker program running elsewhere, put the following in a different project's Program.cs that references the worker project:

using MyNamespace;
using Temporalio.Client;

// Create a client to localhost on "default" namespace
var client = await TemporalClient.ConnectAsync(new("localhost:7233"));

// Run workflow
var result = await client.ExecuteWorkflowAsync(
    (SayHelloWorkflow wf) => wf.RunAsync("Temporal"),
    new(id: "my-workflow-id", taskQueue: "my-task-queue"));

Console.WriteLine("Workflow result: {0}", result);

This will output:

Workflow result: Hello, Temporal!

Usage

Clients

A client can be created and used to start a workflow. For example:

using MyNamespace;
using Temporalio.Client;

// Create client connected to server at the given address and namespace
var client = await TemporalClient.ConnectAsync(new()
{
    TargetHost = "localhost:7233",
    Namespace = "my-namespace",
});

// Start a workflow
var handle = await client.StartWorkflowAsync(
    (MyWorkflow wf) => wf.RunAsync("some workflow argument"),
    new() { ID = "my-workflow-id", TaskQueue = "my-task-queue" });

// Wait for a result
var result = await handle.GetResultAsync();
Console.WriteLine("Result: {0}", result);

Notes about the above code:

  • Temporal clients are not explicitly disposable.
  • To enable TLS, the Tls option can be set to a non-null TlsOptions instance.
  • Instead of StartWorkflowAsync + GetResultAsync above, there is an ExecuteWorkflowAsync extension method that is clearer if the handle is not needed.
  • The type-safe forms of StartWorkflowAsync and ExecuteWorkflowAsync accept a lambda expression that take the workflow as the first parameter and must only call the run method in the lambda.
  • Non-type-safe forms of StartWorkflowAsync and ExecuteWorkflowAsync exist when there is no workflow definition or the workflow may take more than one argument or some other dynamic need. These simply take string workflow type names and an object array for arguments.
  • The handle above represents a WorkflowHandle which has specific workflow operations on it. For existing workflows, handles can be obtained via client.GetWorkflowHandle.

Cloud Client Using MTLS

Assuming a client certificate is present at my-cert.pem and a client key is present at my-key.pem, this is how to connect to Temporal Cloud:

using Temporalio.Client;

var client = await TemporalClient.ConnectAsync(new("my-namespace.a1b2c.tmprl.cloud:7233")
{
    Namespace = "my-namespace.a1b2c",
    Tls = new()
    {
        ClientCert = await File.ReadAllBytesAsync("my-cert.pem"),
        ClientPrivateKey = await File.ReadAllBytesAsync("my-key.pem"),
    },
});

Client Dependency Injection

To create clients for use with dependency injection, see the Temporalio.Extensions.Hosting project which has extension methods for creating singleton clients lazily on service collections.

For manually creating clients for dependency injection, users may prefer TemporalClient.CreateLazy which is a synchronous method which creates a client that does not attempt to connect until the first call is made on it. This can be helpful for dependency injection but beware that deferring connection until later can make it hard to see issues with connection parameters as early as may be expected. However, connection must be made before a worker is created with it.

Data Conversion

Data converters are used to convert raw Temporal payloads to/from actual .NET types. A custom data converter can be set via the DataConverter option when creating a client. Data converters are a combination of payload converters, payload codecs, and failure converters. Payload converters convert .NET values to/from serialized bytes. Payload codecs convert bytes to bytes (e.g. for compression or encryption). Failure converters convert exceptions to/from serialized failures.

Data converters are in the Temporalio.Converters namespace. The default data converter uses a default payload converter, which supports the following types:

  • null
  • byte[]
  • Google.Protobuf.IMessage instances
  • Anything that System.Text.Json supports
  • IRawValue as unconverted raw payloads

Custom converters can be created for all uses. For example, to create client with a data converter that converts all C# property names to camel case, you would:

using System.Text.Json;
using Temporalio.Client;
using Temporalio.Converters;

public class CamelCasePayloadConverter : DefaultPayloadConverter
{
    public CamelCasePayloadConverter()
      : base(new JsonSerializerOptions { PropertyNamingPolicy = JsonNamingPolicy.CamelCase })
    {
    }
}

var client = await TemporalClient.ConnectAsync(new()
{
    TargetHost = "localhost:7233",
    Namespace = "my-namespace",
    DataConverter = DataConverter.Default with { PayloadConverter = new CamelCasePayloadConverter() },
});

Workers

Workers host workflows and/or activities. Here's how to run a worker:

using MyNamespace;
using Temporalio.Client;
using Temporalio.Worker;

// Create client
var client = await TemporalClient.ConnectAsync(new ()
{
    TargetHost = "localhost:7233",
    Namespace = "my-namespace",
});

// Create worker
using var worker = new TemporalWorker(
    client,
    new TemporalWorkerOptions("my-task-queue").
        AddActivity(MyActivities.MyActivity).
        AddWorkflow<MyWorkflow>());

// Run worker until Ctrl+C
using var cts = new CancellationTokenSource();
Console.CancelKeyPress += (sender, eventArgs) =>
{
    eventArgs.Cancel = true;
    cts.Cancel();
};
await worker.ExecuteAsync(cts.Token);

Notes about the above code:

  • This shows how to run a worker from C# using top-level statements. Of course this can be part of a larger program and ExecuteAsync can be used like any other task call with a cancellation token.
  • The worker uses the same client that is used for all other Temporal tasks (e.g. starting workflows).
  • Workers can have many more options not shown here (e.g. data converters and interceptors).

Worker as Generic Host

See the Temporalio.Extensions.Hosting project for support for worker services and client/activity dependency injection.

Workflows

Workflow Definition

Workflows are defined as classes or interfaces with a [Workflow] attribute. The entry point method for a workflow has the [WorkflowRun] attribute. Methods for signals and queries have the [WorkflowSignal] and [WorkflowQuery] attributes respectively. Here is an example of a workflow definition:

using Microsoft.Extensions.Logging;
using Temporalio.Workflow;

public record GreetingParams(string Salutation = "Hello", string Name = "<unknown>");

[Workflow]
public class GreetingWorkflow
{
    private string? currentGreeting;
    private GreetingParams? greetingParamsUpdate;
    private bool complete;

    [WorkflowRun]
    public async Task<string> RunAsync(GreetingParams initialParams)
    {
        var greetingParams = initialParams;
        while (true)
        {
            // Call activity to create greeting and store as field
            currentGreeting = await Workflow.ExecuteActivityAsync(
                // This is a static activity method. If it were an instance
                // method, a typed parameter can be accepted in the lambda call.
                () => GreetingActivities.CreateGreeting(greetingParams),
                new() { ScheduleToCloseTimeout = TimeSpan.FromMinutes(5) });
            Workflow.Logger.LogDebug("Greeting set to {Greeting}", currentGreeting);

            // Wait for param update or complete signal. Note, cancellation can
            // occur by default on WaitConditionAsync calls so cancellation
            // token does not need to be passed explicitly.
            var waitUpdate = Workflow.WaitConditionAsync(() => greetingParamsUpdate != null);
            var waitComplete = Workflow.WaitConditionAsync(() => complete);
            if (waitComplete == await Task.WhenAny(waitUpdate, waitComplete))
            {
                // Just return the greeting
                return currentGreeting!;
            }
            // We know it was an update, so update it and continue
            greetingParams = greetingParamsUpdate!;
            greetingParamsUpdate = null;
        }
    }

    // WARNING: Workflow updates are experimental
    [WorkflowUpdate]
    public async Task UpdateGreetingParamsAsync(GreetingParams greetingParams) =>
      this.greetingParamsUpdate = greetingParams;

    [WorkflowSignal]
    public async Task CompleteWithGreetingAsync() => this.complete = true;

    [WorkflowQuery]
    public string CurrentGreeting() => currentGreeting;
}

Notes about the above code:

  • Interfaces and abstract methods can have these attributes. This is helpful for defining a workflow implemented elsewhere. But if/when implemented, all pieces of the implementation should have the attributes too.
  • This workflow continually updates the greeting params when signalled and can complete with the greeting when given a different signal
  • Workflow code must be deterministic. See the "Workflow Logic Constraints" section below.
  • Workflow.ExecuteActivityAsync is strongly typed and accepts a lambda expression. This activity call can be a sync or async function, return a value or not, and invoked statically or on an instance (which would require accepting the instance as the only lambda parameter).

Attributes that can be applied:

  • [Workflow] attribute must be present on the workflow type.
    • The attribute can have a string argument for the workflow type name. Otherwise the name is defaulted to the unqualified type name (with the I prefix removed if on an interface and has a capital letter following).
    • Dynamic = true can be set for the workflow which makes the workflow a dynamic workflow meaning it will be called when no other workflows match. The run call must accept a single parameter of Temporalio.Converters.IRawValue[] for the arguments. Only one dynamic workflow may be registered on a worker.
  • [WorkflowRun] attribute must be present on one and only one public method.
    • The workflow run method must return a Task or Task<>.
    • The workflow run method should accept a single parameter and return a single type. Records are encouraged because optional fields can be added without affecting backwards compatibility of the workflow definition.
    • The parameters of this method and its return type are considered the parameters and return type of the workflow itself.
    • This attribute is not inherited and this method must be explicitly defined on the declared workflow type. Even if the method functionality should be inherited, for clarity reasons it must still be explicitly defined even if it just invokes the base class method.
  • [WorkflowSignal] attribute may be present on any public method that handles signals.
    • Signal methods must return a Task.
    • The attribute can have a string argument for the signal name. Otherwise the name is defaulted to the unqualified method name with Async trimmed off the end if it is present.
    • This attribute is not inherited and therefore must be explicitly set on any override.
    • Dynamic = true can be set for the signal which makes the signal a dynamic signal meaning it will be called when no other signals match. The call must accept a string for the signal name and Temporalio.Converters.IRawValue[] for the arguments. Only one dynamic signal may be present on a workflow.
  • [WorkflowQuery] attribute may be present on any public method or property with public getter that handles queries.
    • Query methods must be non-void but cannot return a Task (i.e. they cannot be async).
    • The attribute can have a string argument for the query name. Otherwise the name is defaulted to the unqualified method name.
    • This attribute is not inherited and therefore must be explicitly set on any override.
    • Dynamic = true can be set for the query which makes the query a dynamic query meaning it will be called when no other queries match. The call must accept a string for the query name and Temporalio.Converters.IRawValue[] for the arguments. Only one dynamic query may be present on a workflow.
  • [WorkflowUpdate] attribute may be present on any public method that handles updates.
    • Update methods must return a Task (can be a Task<TResult>).
    • The attribute can have a string argument for the update name. Otherwise the name is defaulted to the unqualified method name with Async trimmed off the end if it is present.
    • This attribute is not inherited and therefore must be explicitly set on any override.
    • Dynamic = true can be set for the update which makes the update a dynamic update, meaning it will be called when no other updates match. The call must accept a string for the update name and Temporalio.Converters.IRawValue[] for the arguments. Only one dynamic update may be present on a workflow.
    • A validator method can be created that is marked with the [WorkflowUpdateValidator(nameof(MyUpdateMethod))] attribute. It must be void but accept the exact same parameters as the update method. This must be a read-only method and if an exception is thrown, the update is failed without being stored in history.
Workflow Inheritance

Workflows can inherit from interfaces and base classes. Callers can use these interfaces to make calls for a workflow without the implementation present. This can be valuable in separating logic, but there are some details that should be noted.

[Workflow] and [WorkflowRun] attributes are never inherited and must be defined on item that is actually registered with the worker. This means even if an interface or base class has these, they must also be present on the final implementing class. So if a base class has a full [WorkflowRun] implementation, the subclass must override that method, set [WorkflowRun] on the override, and then it can delegate to the base class. This explicit non-inheritance strategy was intentionally done to avoid diamond problems with workflows and to let readers clearly know whether a class is a workflow (including the name defaulted) and what its entry point is. A workflow can only have one [WorkflowRun] method.

[WorkflowSignal], [WorkflowQuery], and [WorkflowUpdate] methods can be inherited from base classes/interfaces if the method is not overridden. However, if the method is declared in the subclass, it must also have these attributes. The attributes themselves are not inherited.

Running Workflows

To start a workflow from a client, you can StartWorkflowAsync with a lambda expression and then use the resulting handle:

// Start the workflow
var arg = new GreetingParams(Name: "Temporal");
var handle = await client.StartWorkflowAsync(
    (GreetingWorkflow wf) => wf.RunAsync(arg),
    new(id: "my-workflow-id", taskQueue: "my-task-queue"));
// Check current greeting via query
Console.WriteLine(
    "Current greeting: {0}",
    await handle.QueryAsync(wf => wf.CurrentGreeting()));
// Change the params via update
var updateArg = new GreetingParams(Salutation: "Aloha", Name: "John");
await handle.ExecuteUpdateAsync(wf => wf.UpdateGreetingParamsAsync(updateArg));
// Tell it to complete via signal
await handle.SignalAsync(wf => wf.CompleteWithGreetingAsync());
// Wait for workflow result
Console.WriteLine(
    "Final greeting: {0}",
    await handle.GetResultAsync());

Some things to note about the above code:

  • This uses the GreetingWorkflow from the previous section.
  • The output of this code is "Current greeting: Hello, Temporal!" and "Final greeting: Aloha, John!".
  • ID and task queue are required for starting a workflow.
  • All calls here are typed. For example, using something besides GreetingParams for the parameter of StartWorkflowAsync would be a compile-time failure.
  • The handle is also typed with the workflow result, so GetResultAsync() returns a string as expected.
  • A shortcut extension ExecuteWorkflowAsync is available that is just StartWorkflowAsync + GetResultAsync.
  • SignalWithStart method is present on the workflow options to make the workflow call a signal-with-start call which means it will only start the workflow if it's not running, but send a signal to it regardless.

Invoking Activities

  • Activities are executed with Workflow.ExecuteActivityAsync which accepts a lambda expression that invokes the activity with its arguments. The activity method can be sync or async, return a result or not, and be static or an instance method (which would require the parameter of the lambda to be the instance type).
  • A non-type-safe form of ExecuteActivityAsync exists that just accepts a string activity name.
  • Activity options are a simple class set after the lambda expression or name.
    • These options must be present and either ScheduleToCloseTimeout or StartToCloseTimeout must be present.
    • Retry policy, cancellation type, etc can also be set on the options.
    • Cancellation token is defaulted as the workflow cancellation token, but an alternative can be given in options. When the token is cancelled, a cancellation request is sent to the activity. How that is handled depends on cancellation type.
  • Activity failures are thrown from the task as ActivityFailureException.
  • ExecuteLocalActivityAsync exists with mostly the same options for local activities.

Invoking Child Workflows

  • Child workflows are started with Workflow.StartChildWorkflowAsync which accepts a lambda expression whose parameter is the child workflow to call and the expression is a call to its run method with arguments.
  • A non-type-safe form of StartChildWorkflowAsync exists that just accepts a string workflow name.
  • Child workflow options are a simple class set after after the lambda expression or name.
    • These options are optional.
    • Retry policy, ID, etc can also be set on the options.
    • Cancellation token is defaulted as the workflow cancellation token, but an alternative can be given in options. When the token is cancelled, a cancellation request is sent to the child workflow. How that is handled depends on cancellation type.
  • Result of a child workflow starting is a ChildWorkflowHandle which has the ID, GetResultAsync for getting the result, and SignalAsync for signalling the child.
  • The task for starting a child workflow does not complete until the start has been accepted by the server.
  • A shortcut of Workflow.ExecuteChildWorkflowAsync is available which is StartChildWorkflowAsync + GetResultAsync for those only needing to wait on its result.

Timers and Conditions

  • A timer is represented by Workflow.DelayAsync.
    • Timers are also started on Workflow.WaitConditionAsync when a timeout is specified.
    • This can accept a cancellation token, but if none given, defaults to Workflow.CancellationToken.
    • Task.Delay or any other .NET timer-related call cannot be used in workflows because workflows must be deterministic. See the "Workflow Logic Constraints" section below.
  • Workflow.WaitConditionAsync accepts a function that, when it returns true, the Task is completed successfully.
    • The function is invoked on each iteration of the internal event loop. This is commonly used for checking if a variable is changed from some other part of a workflow (e.g. a signal handler).
    • A timeout can be provided for the wait condition which uses a timer.
    • This can accept a cancellation token, but if none given, defaults to Workflow.CancellationToken.

Workflow Task Scheduling and Cancellation

Workflows are backed by a custom, deterministic TaskScheduler. All async calls inside a workflow must use this scheduler (i.e. TaskScheduler.Current) and not the default thread-pool-based one (i.e. TaskScheduler.Default). See "Workflow Logic Constraints" on what to avoid to make sure the proper task scheduler is used.

Every workflow contains a cancellation token at Workflow.CancellationToken. This token is cancelled when the workflow is cancelled. For all workflow calls that accept a cancellation token, this is the default. So if a workflow is waiting on ExecuteActivityAsync and the workflow is cancelled, that cancellation will propagate to the waiting activity.

Cancellation token sources may be used to perform cancellation more specifically. A cancellation token derived from the workflow one can be created via CancellationTokenSource.CreateLinkedTokenSource(Workflow.CancellationToken). Then that source can be used to cancel something more specifically. Or, in cases where cleanup code may need to be run during cancellation such as in a finally block, a new unlinked cancellation token source can be constructed that will not be seen as cancelled even though the workflow is cancelled.

Like in other areas of .NET, cancellation tokens must be respected in order to properly cancel the workflow. Yet for most use cases where await calls yield to Temporal, the default cancellation token at the workflow level is good enough.

Workflow Utilities

In addition to the pieces documented above, additional properties/methods are statically available on Workflow that can be used from workflows including:

  • Properties:
    • Info - Immutable workflow info.
    • InWorkflow - Boolean saying whether the current code is running in a workflow. This is the only call that won't throw an exception when accessed outside of a workflow.
    • Logger - Scoped replay-aware logger for use inside a workflow. Normal loggers should not be used because they may log duplicate values during replay.
    • Memo - Read-only current memo values.
    • PayloadConverter - Can be used if IRawValue is used for input or output.
    • Queries - Mutable set of query definitions for the workflow. Technically this can be mutated to add query definitions at runtime, but methods with the [WorkflowQuery] attribute are strongly preferred.
    • Random - Deterministically seeded random instance for use inside workflows.
    • TypedSearchAttributes - Read-only current search attribute values.
    • UtcNow - Deterministic value for the current DateTime.
    • Unsafe.IsReplaying - For advanced users to know whether the workflow is replaying. This is rarely needed.
  • Methods:
    • CreateContinueAsNewException - Create exception that can be thrown to perform a continue-as-new on the workflow. There are several overloads to properly accept a lambda expression for the workflow similar to start/execute workflow calls elsewhere.
    • GetExternalWorkflowHandle - Get a handle to an external workflow to issue cancellation requests and signals.
    • NewGuid - Create a deterministically random UUIDv4 GUID.
    • Patched and DeprecatePatch - Support for patch-based versioning inside the workflow.
    • UpsertMemo - Update the memo values for the workflow.
    • UpsertTypedSearchAttributes - Update the search attributes for the workflow.

Workflow Exceptions

  • Workflows can throw exceptions to fail the workflow/update or the "workflow task" (i.e. suspend the workflow, retrying until code update allows it to continue).
  • By default, exceptions that are instances of Temporalio.Exceptions.FailureException will fail the workflow/update with that exception.
    • For failing the workflow/update explicitly with a user exception, explicitly throw Temporalio.Exceptions.ApplicationFailureException. This can be marked non-retryable or include details as needed.
    • Other exceptions that come from activity execution, child execution, cancellation, etc are already instances of FailureException (or TaskCanceledException) and will fail the workflow/update if uncaught.
  • By default, all other exceptions fail the "workflow task" which means the workflow/update will continually retry until the code is fixed. This is helpful for bad code or other non-predictable exceptions. To actually fail the workflow/update, use an ApplicationFailureException as mentioned above.
  • By default, all non-deterministic exceptions that are detected internally fail the "workflow task".

The default behavior can be customized at the worker level for all workflows via the TemporalWorkerOptions.WorkflowFailureExceptionTypes property or per workflow via the FailureExceptionTypes property on the WorkflowAttribute. When a workflow encounters a "workflow task" fail (i.e. suspend), it will first check either of these collections to see if the exception is an instance of any of the types and if so, will turn into a workflow/update failure. As a special case, when a non-deterministic exception occurs and Temporalio.Exceptions.WorkflowNondeterminismException is assignable to any of the types in the collection, that too will turn into a workflow/update failure. However non-deterministic exceptions that match during update handlers become workflow failures not update failures like other exceptions because a non-deterministic exception is an entire-workflow-failure situation.

⚠️ WARNING: Customizing the default behavior is currently experimental and the default behavior may change in the future.

Workflow Logic Constraints

Temporal Workflows must be deterministic which includes .NET workflows. This means there are several things workflows cannot do such as:

  • Perform IO (network, disk, stdio, etc)
  • Access/alter external mutable state
  • Do any threading
  • Do anything using the system clock (e.g. DateTime.Now)
    • This includes .NET timers (e.g. Task.Delay or Thread.Sleep)
  • Make any random calls
  • Make any not-guaranteed-deterministic calls (e.g. iterating over a dictionary)

In the future, an analyzer may be written to help catch some of these mistakes at compile time. In the meantime, due to .NET's lack of a sandbox, there is not a good way to prevent non-deterministic calls so developers need to be vigilant.

.NET Task Determinism

Some calls in .NET do unsuspecting non-deterministic things and are easy to accidentally use. This is especially true with Tasks. Temporal requires that the deterministic TaskScheduler.Current is used, but many .NET async calls will use TaskScheduler.Default implicitly (and some analyzers even encourage this). Here are some known gotchas to avoid with .NET tasks inside of workflows:

  • Do not use Task.Run - this uses the default scheduler and puts work on the thread pool.
    • Use Workflow.RunTaskAsync instead.
    • Can also use Task.Factory.StartNew with current scheduler or instantiate the Task and run Task.Start on it.
  • Do not use Task.ConfigureAwait(false) - this will not use the current context.
    • If you must use Task.ConfigureAwait, use Task.ConfigureAwait(true).
    • There is no significant performance benefit to Task.ConfigureAwait in workflows anyways due to how the scheduler works.
  • Do not use anything that defaults to the default task scheduler.
  • Do not use Task.Delay, Task.Wait, timeout-based CancellationTokenSource, or anything that uses .NET built-in timers.
    • Workflow.DelayAsync, Workflow.WaitConditionAsync, or non-timeout-based cancellation token source is suggested.
  • Do not use Task.WhenAny.
    • Use Workflow.WhenAnyAsync instead.
    • Technically this only applies to an enumerable set of tasks with results or more than 2 tasks with results. Other uses are safe. See this issue.
  • Do not use Task.WhenAll
    • Use Workflow.WhenAllAsync instead.
    • Technically Task.WhenAll is currently deterministic in .NET and safe, but it is better to use the wrapper to be sure.
  • Do not use CancellationTokenSource.CancelAsync.
    • Use CancellationTokenSource.Cancel instead.
  • Do not use System.Threading.Semaphore or System.Threading.SemaphoreSlim or System.Threading.Mutex.
    • Use Temporalio.Workflows.Semaphore or Temporalio.Workflows.Mutex instead.
    • Technically SemaphoreSlim does work if only the async form of WaitAsync is used without no timeouts and Release is used. But anything else can deadlock the workflow and its use is cumbersome since it must be disposed.
  • Be wary of additional libraries' implicit use of the default scheduler.
    • For example, while there are articles for Dataflow about using a specific scheduler, there are hidden implicit uses of TaskScheduler.Default. For example, see this bug.

In order to help catch wrong scheduler use, by default the Temporal .NET SDK adds an event source listener for info-level task events. While this technically receives events from all uses of tasks in the process, we make sure to ignore anything that is not running in a workflow in a high performant way (basically one thread local check). For code that does run in a workflow and accidentally starts a task in another scheduler, an InvalidWorkflowOperationException will be thrown which "pauses" the workflow (fails the workflow task which continually retries until the code is fixed.). This is unfortunately a runtime-only check, but can help catch mistakes early. If this needs to be turned off for any reason, set DisableWorkflowTracingEventListener to true in worker options.

In the near future for modern .NET versions we hope to use the new TimeProvider API which will allow us to control current time and timers.

Workflow .editorconfig

Since workflow code follows some different logic rules than regular C# code, there are some common analyzer rules out there that developers may want to disable. To ensure these are only disabled for workflows, current recommendation is to use the .workflow.cs extension for files containing workflows.

Here are the rules to disable:

  • CA1024 - This encourages properties instead of methods that look like getters. However for reflection reasons we cannot use property getters for queries, so it is very normal to have

    [WorkflowQuery]
public string GetSomeThing() => someThing;

  • CA1822 - This encourages static methods when methods don't access instance state. Workflows however use instance methods for run, signals, queries, or updates even if they could be static.

  • CA2007 - This encourages users to use ConfigureAwait instead of directly waiting on a task. But in workflows, there is no benefit to this and it just adds noise (and if used, needs to be ConfigureAwait(true) not ConfigureAwait(false)).

  • CA2008 - This encourages users to always apply an explicit task scheduler because the default of TaskScheduler.Current is bad. But for workflows, the default of TaskScheduler.Current is good/required.

  • CA5394 - This discourages use of non-crypto random. But deterministic workflows, via Workflow.Random intentionally provide a deterministic non-crypto random instance.

  • CS1998 - This discourages use of async on async methods that don't await. But workflows handlers like signals are often easier to write in one-line form this way, e.g. public async Task SignalSomethingAsync(string value) => this.value = value;.

  • VSTHRD105 - This is similar to CA2008 above in that use of implicit current scheduler is discouraged. That does not apply to workflows where it is encouraged/required.

Here is the .editorconfig snippet for the above which may frequently change as we learn more:

##### Configuration specific for Temporal workflows #####
[*.workflow.cs]

# We use getters for queries, they cannot be properties
dotnet_diagnostic.CA1024.severity = none

# Don't force workflows to have static methods
dotnet_diagnostic.CA1822.severity = none

# Do not need ConfigureAwait for workflows
dotnet_diagnostic.CA2007.severity = none

# Do not need task scheduler for workflows
dotnet_diagnostic.CA2008.severity = none

# Workflow randomness is intentionally deterministic
dotnet_diagnostic.CA5394.severity = none

# Allow async methods to not have await in them
dotnet_diagnostic.CS1998.severity = none

# Don't avoid, but rather encourage things using TaskScheduler.Current in workflows
dotnet_diagnostic.VSTHRD105.severity = none

Workflow Testing

Workflow testing can be done in an integration-test fashion against a real server, however it is hard to simulate timeouts and other long time-based code. Using the time-skipping workflow test environment can help there.

A non-time-skipping Temporalio.Testing.WorkflowEnvironment can be started via StartLocalAsync which supports all standard Temporal features. It is actually a real Temporal server lazily downloaded on first use and run as a sub-process in the background.

A time-skipping Temporalio.Testing.WorkflowEnvironment can be started via StartTimeSkippingAsync which is a reimplementation of the Temporal server with special time skipping capabilities. This too lazily downloads the process to run when first called. Note, this class is not thread safe nor safe for use with independent tests. It can be reused, but only for one test at a time because time skipping is locked/unlocked at the environment level.

Automatic Time Skipping

Anytime a workflow result is waiting on, the time-skipping server automatically advances to the next event it can. To manually advance time before waiting on the result of the workflow, the WorkflowEnvironment.DelayAsync method can be used. If an activity is running, time-skipping is disabled.

Here's a simple example of a workflow that sleeps for 24 hours:

using Temporalio.Workflows;

[Workflow]
public class WaitADayWorkflow
{
    [WorkflowRun]
    public async Task<string> RunAsync()
    {
        await Workflow.DelayAsync(TimeSpan.FromDays(1));
        return "all done";
    }
}

A regular integration test of this workflow on a normal server would be way too slow. However, the time-skipping server automatically skips to the next event when we wait on the result. Here's a test for that workflow:

using Temporalio.Testing;
using Temporalio.Worker;

[Fact]
public async Task WaitADayWorkflow_SimpleRun_Succeeds()
{
    await using var env = await WorkflowEnvironment.StartTimeSkippingAsync();
    using var worker = new TemporalWorker(
      env.Client,
      new TemporalWorkerOptions($"task-queue-{Guid.NewGuid()}").
          AddWorkflow<WaitADayWorkflow>());
    await worker.ExecuteAsync(async () =>
    {
        var result = await env.Client.ExecuteWorkflowAsync(
            (WaitADayWorkflow wf) => wf.RunAsync(),
            new(id: $"wf-{Guid.NewGuid()}", taskQueue: worker.Options.TaskQueue!));
        Assert.Equal("all done", result);
    });
}

This test will run almost instantly. This is because by calling ExecuteWorkflowAsync on our client, we are actually calling StartWorkflowAsync + GetResultAsync, and GetResultAsync automatically skips time as much as it can (basically until the end of the workflow or until an activity is run).

To disable automatic time-skipping while waiting for a workflow result, run code as a lambda passed to env.WithAutoTimeSkippingDisabled or env.WithAutoTimeSkippingDisabledAsync.

Manual Time Skipping

Until a workflow is waited on, all time skipping in the time-skipping environment is done manually via WorkflowEnvironment.DelayAsync.

Here's a workflow that waits for a signal or times out:

using Temporalio.Workflows;

[Workflow]
public class SignalWorkflow
{
    private bool signalReceived = false;

    [WorkflowRun]
    public async Task<string> RunAsync()
    {
        // Wait for signal or timeout in 45 seconds
        if (Workflow.WaitConditionAsync(() => signalReceived, TimeSpan.FromSeconds(45)))
        {
            return "got signal";
        }
        return "got timeout";
    }

    [WorkflowSignal]
    public async Task SomeSignalAsync() => signalReceived = true;
}

To test a normal signal, you might:

using Temporalio.Testing;
using Temporalio.Worker;

[Fact]
public async Task SignalWorkflow_SendSignal_HasExpectedResult()
{
    await using var env = WorkflowEnvironment.StartTimeSkippingAsync();
    using var worker = new TemporalWorker(
        env.Client,
        new TemporalWorkerOptions($"task-queue-{Guid.NewGuid()}").
            AddWorkflow<SignalWorkflow>());
    await worker.ExecuteAsync(async () =>
    {
        var handle = await env.Client.StartWorkflowAsync(
            (SignalWorkflow wf) => wf.RunAsync(),
            new(id: $"wf-{Guid.NewGuid()}", taskQueue: worker.Options.TaskQueue!));
        await handle.SignalAsync(wf => wf.SomeSignalAsync());
        Assert.Equal("got signal", await handle.GetResultAsync());
    });
}

But how would you test the timeout part? Like so:

using Temporalio.Testing;
using Temporalio.Worker;

[Fact]
public async Task SignalWorkflow_SignalTimeout_HasExpectedResult()
{
    await using var env = WorkflowEnvironment.StartTimeSkippingAsync();
    using var worker = new TemporalWorker(
        env.Client,
        new TemporalWorkerOptions($"task-queue-{Guid.NewGuid()}").
            AddWorkflow<SignalWorkflow>());
    await worker.ExecuteAsync(async () =>
    {
        var handle = await env.Client.StartWorkflowAsync(
            (SignalWorkflow wf) => wf.RunAsync(),
            new(id: $"wf-{Guid.NewGuid()}", taskQueue: worker.Options.TaskQueue!));
        await env.DelayAsync(TimeSpan.FromSeconds(50));
        Assert.Equal("got timeout", await handle.GetResultAsync());
    });
}
Mocking Activities

When testing workflows, often you don't want to actually run the activities. Activities are just functions with the [Activity] attribute. Simply write different/empty/fake/asserting ones and pass those to the worker to have different activities called during the test.

Workflow Replay

Given a workflow's history, it can be replayed locally to check for things like non-determinism errors. For example, assuming the history parameter below is given a JSON string of history exported from the CLI or web UI, the following function will replay it:

using Temporalio;
using Temporalio.Worker;

public static async Task ReplayFromJsonAsync(string historyJson)
{
    var replayer = new WorkflowReplayer(
      new WorkflowReplayerOptions().AddWorkflow<MyWorkflow>());
    await replayer.ReplayWorkflowAsync(WorkflowHistory.FromJson("my-workflow-id", historyJson));
}

If there is a non-determinism, this will throw an exception.

Workflow history can be loaded from more than just JSON. It can be fetched individually from a workflow handle, or even in a list. For example, the following code will check that all workflow histories for a certain workflow type (i.e. workflow class) are safe with the current workflow code.

using Temporalio;
using Temporalio.Client;
using Temporalio.Worker;

public static async Task CheckPastHistoriesAysnc(ITemporalClient client)
{
    var replayer = new WorkflowReplayer(
      new WorkflowReplayerOptions().AddWorkflow<MyWorkflow>());
    var listIter = client.ListWorkflowHistoriesAsync("WorkflowType = 'SayHello'");
    await foreach (var result in replayer.ReplayWorkflowsAsync(listIter))
    {
        if (result.ReplayFailure != null)
        {
            ExceptionDispatchInfo.Throw(result.ReplayFailure);
        }
    }
}

Activities

Activity Definition

Activities are methods with the [Activity] annotation like so:

namespace MyNamespace;

using System.Net.Http;
using System.Threading.Tasks;
using System.Timers;
using Temporalio.Activities;

public static class MyActivities
{
    private static readonly HttpClient client = new();

    [Activity]
    public static async Task<string> GetPageAsync(string url)
    {
        // Heartbeat every 2s
        using var timer = new Timer(2000)
        {
            AutoReset = true,
            Enabled = true,
        };
        timer.Elapsed += (sender, eventArgs) => ActivityExecutionContext.Current.Heartbeat();

        // Issue our HTTP call
        using var response = await client.GetAsync(url, ActivityExecutionContext.Current.CancellationToken);
        response.EnsureSuccessStatusCode();
        return await response.Content.ReadAsStringAsync(ActivityExecutionContext.Current.CancellationToken);
    }
}

Notes about activity definitions:

  • All activities must have the [Activity] attribute.
  • [Activity] can be given a custom string name.
    • If unset, the default is the method's unqualified name. If the method name ends with Async and returns a Task, the default name will have Async trimmed off the end.
  • Long running activities should heartbeat to regularly to inform server the activity is still running.
    • Heartbeats are throttled internally, so users can call this frequently without fear of calling too much.
    • Activities must heartbeat to receive cancellation.
  • Activities can be defined on static or instance methods. They can even be lambdas or local methods, but rarely is this valuable since often an activity will be referenced by a workflow.
  • Activities can be synchronous or asynchronous. If an activity returns a Task, that task is awaited on as part of the activity.
  • [Activity(Dynamic = true) represents a dynamic activity meaning it will be called when no other activities match. The call must accept a single parameter of Temporalio.Converters.IRawValue[] for the arguments. Only one dynamic activity may be registered on a worker.

Activity Dependency Injection

To have activity classes instantiated via a DI container to support dependency injection, see the Temporalio.Extensions.Hosting project which supports worker services in addition to activity dependency injection.

Activity Execution Context

During activity execution, an async-local activity context is available via ActivityExecutionContext.Current. This will throw if not currently in an activity context (which can be checked with ActivityExecutionContext.HasCurrent). It contains the following important members:

  • Info - Information about the activity.
  • Logger - A logger scoped to the activity.
  • CancelReason - If CancellationToken is cancelled, this will contain the reason.
  • CancellationToken - Token cancelled when the activity is cancelled.
  • Heartbeat(object?...) - Send a heartbeat from this activity.
  • WorkerShutdownToken - Token cancelled on worker shutdown before the grace period + CancellationToken cancellation.
  • PayloadConverter - Can be used if IRawValue is used for input or output.

Activity Heartbeating and Cancellation

In order for a non-local activity to be notified of cancellation requests, it must invoke ActivityExecutionContext.Current.Heartbeat(). It is strongly recommended that all but the fastest executing activities call this function regularly.

In addition to obtaining cancellation information, heartbeats also support detail data that is persisted on the server for retrieval during activity retry. If an activity calls ActivityExecutionContext.Current.Heartbeat(123) and then fails and is retried, ActivityExecutionContext.Current.Info.HeartbeatDetails will contain the last detail payloads. A helper can be used to convert, so await ActivityExecutionContext.Current.Info.HeartbeatDetailAtAsync<int>(0) would give 123 on the next attempt.

Heartbeating has no effect on local activities.

Activity Worker Shutdown

An activity can react to a worker shutdown specifically.

Upon worker shutdown, ActivityExecutionContext.WorkerShutdownToken is cancelled. Then the worker will wait a grace period set by the GracefulShutdownTimeout worker option (default as 0) before issuing actual cancellation to all still-running activities via ActivityExecutionContext.CancellationToken.

Worker shutdown will wait on all activities to complete, so if a long-running activity does not respect cancellation, the shutdown may never complete.

Activity Testing

Unit testing an activity or any code that could run in an activity is done via the Temporalio.Testing.ActivityEnvironment class. Simply instantiate the class, and any function passed to RunAsync will be invoked inside the activity context. The following important members are available on the environment to affect the activity context:

  • Info - Activity info, defaulted to a basic set of values.
  • Logger - Activity logger, defaulted to a null logger.
  • Cancel(CancelReason) - Helper to set the reason and cancel the source.
  • CancelReason - Cancel reason.
  • CancellationTokenSource - Token source for issuing cancellation.
  • Heartbeater - Callback invoked each heartbeat.
  • WorkerShutdownTokenSource - Token source for issuing worker shutdown.
  • PayloadConverter - Defaulted to default payload converter.

OpenTelemetry Tracing Support

See the OpenTelemetry extension.

Built-in Native Shared Library

This SDK requires a built-in unmanaged, native shared library built in Rust. It is named temporal_sdk_bridge.dll on Windows, libtemporal_sdk_bridge.so on Linux, and libtemporal_sdk_bridge.dylib on macOS. This is automatically included when using modern versions of .NET on a common platform. If you are using .NET framework, you may have to explicitly set the platform to x64 or arm64 because AnyCPU will not choose the proper library.

Currently we only support RIDs linux-arm64, linux-x64, osx-arm64, osx-x64, and win-x64. Any other platforms needed (e.g. linux-musl-x64 on Alpine) will require a custom build.

The native shared library on Windows does require a Visual C++ runtime. Some containers, such as Windows Nano Server, do not include this runtime. If not available, users may have to manually copy this runtime (usually just vcruntime140.dll), depend on a NuGet package that has it, or install the Visual C++ runtime (often via Visual C++ Redistributable installation).

If the native shared library is not loading for whatever reason, the following error may appear:

System.DllNotFoundException: Unable to load DLL 'temporal_sdk_bridge' or one of its dependencies: The specified module could not be found.

See the earlier part of this section for details on what environments are supported.

Development

Build

Prerequisites:

With all prerequisites in place, run:

dotnet build

Or for release:

dotnet build --configuration Release

Code formatting

This project uses StyleCop analyzers with some overrides in .editorconfig. To format, run:

dotnet format

Can also run with --verify-no-changes to ensure it is formatted.

VisualStudio Code

When developing in vscode, the following JSON settings will enable StyleCop analyzers:

    "omnisharp.enableEditorConfigSupport": true,
    "omnisharp.enableRoslynAnalyzers": true

Testing

Run:

dotnet test

Can add options like:

  • --logger "console;verbosity=detailed" to show logs
  • --filter "FullyQualifiedName=Temporalio.Tests.Client.TemporalClientTests.ConnectAsync_Connection_Succeeds" to run a specific test
  • --blame-crash to do a host process dump on crash

To help debug native pieces and show full stdout/stderr, this is also available as an in-proc test program. Run:

dotnet run --project tests/Temporalio.Tests

Extra args can be added after --, e.g. -- -verbose would show verbose logs and -- --help would show other options. If the arguments are anything but --help, the current assembly is prepended to the args before sending to the xUnit runner.

The following environment variables can be set to override the environment:

  • TEMPORAL_TEST_CLIENT_TARGET_HOST - This must be set for any of the variables below to apply
  • TEMPORAL_TEST_CLIENT_NAMESPACE - Required if the above is set
  • TEMPORAL_TEST_CLIENT_CERT - Optional, must be present if below is
  • TEMPORAL_TEST_CLIENT_KEY - Optional, must be present if above is

Rebuilding Rust extension and interop layer

To regen core interop from header, install ClangSharpPInvokeGenerator like:

dotnet tool install --global ClangSharpPInvokeGenerator

Then, run:

ClangSharpPInvokeGenerator @src/Temporalio/Bridge/GenerateInterop.rsp

The Rust DLL is built automatically when the project is built. protoc may need to be on the PATH to build the Rust DLL.

This can be annoying to install on linux - so alternatively, publish your PR and you can download the patch from the windows build when it fails because of a mismatch. It uploads the patch as an artifact.

Regenerating protos

Must have protoc on the PATH. Note, for now users should use protoc 23.x until our GH action downloader can support later versions. Here is the latest 23.x release as of this writing.

Then:

dotnet run --project src/Temporalio.Api.Generator

Regenerating API docs

Install docfx, then run:

docfx src/Temporalio.ApiDoc/docfx.json

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Temporal .NET SDK

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