# Cancellation - Rust SDK

You can interrupt a Workflow Execution in one of the following ways:

- [Cancel](#cancellation): Canceling a Workflow provides a graceful way to stop Workflow Execution.
- [Terminate](#termination): Terminating a Workflow forcefully stops Workflow Execution.

Terminating a Workflow forcefully stops Workflow Execution. This action resembles killing a process.

- The system records a `WorkflowExecutionTerminated` event in the Event History.
- The termination forcefully and immediately stops the Workflow Execution.
- The Workflow code gets no chance to handle termination.
- A Workflow Task doesn't get scheduled.

In most cases, canceling is preferable because it allows the Workflow to finish gracefully. Terminate only if the
Workflow is stuck and cannot be canceled normally.

## Cancel a Workflow Execution 

Canceling a Workflow provides a graceful way to stop Workflow Execution. This action resembles sending a `SIGTERM` to a
process.

- The system records a `WorkflowExecutionCancelRequested` event in the Event History.
- A Workflow Task gets scheduled to process the cancelation.
- The Workflow code can handle the cancelation and execute any cleanup logic.
- The system doesn't forcefully stop the Workflow.

To cancel a Workflow Execution in Rust, use the `cancel` method on the Workflow handler:

```rust
let handle = client.start_workflow(
    GreetingsWorkflow::run, 
    (), 
    WorkflowStartOptions::new("my-task-queue", "greetings-workflow-10").build()
).await?;

handle.cancel(WorkflowCancelOptions::builder().reason("No longer needed").build()).await?;
````

### Cancel an Activity from a Workflow 

Canceling an Activity from within a Workflow requires that the Activity Execution sends Heartbeats and sets a Heartbeat
Timeout. If the Heartbeat is not invoked, the Activity cannot receive a cancellation request. When any non-immediate
Activity is executed, the Activity Execution should send Heartbeats and set a
[Heartbeat Timeout](/encyclopedia/detecting-activity-failures#heartbeat-timeout) to ensure that the server knows it is
still working.

When an Activity is canceled, an error is returned in the Activity at the next available opportunity. If cleanup logic
needs to be performed, it can be done when handling the cancellation error. However, for the Activity to appear canceled
the error must be propagated.

Example of a cancellable Activity in Rust:

```rust
#![allow(unreachable_pub)]
use temporalio_macros::{activities};
use temporalio_sdk::{
    activities::{ActivityContext, ActivityError},
};

pub struct CancellationActivities;

#[activities]
impl CancellationActivities {
    #[activity]
    pub async fn long_running_cancellable_activity(
        ctx: ActivityContext,
        _input: (),
    ) -> Result<String, ActivityError> {
        loop {
            if ctx.is_cancelled() {
                return Err(ActivityError::cancelled());
            }
            ctx.record_heartbeat(vec![]);
            tokio::time::sleep(std::time::Duration::from_millis(200)).await;
        }
    }

    #[activity]
    pub async fn cleanup(_ctx: ActivityContext, _input: ()) -> Result<String, ActivityError> {
        Ok("cleanup done".to_string())
    }
}
```

Canceling the Activity from a Workflow:

```rust
fn activity_opts() -> ActivityOptions {
    ActivityOptions::with_start_to_close_timeout(Duration::from_secs(300))
        .heartbeat_timeout(Duration::from_secs(5))
        .build()
}

#[workflow_methods]
impl CancellationWorkflow {
    #[run]
    pub async fn run(ctx: &mut WorkflowContext<Self>, _input: ()) -> WorkflowResult<String> {
        let mut activity_fut = ctx.start_activity(
            CancellationActivities::long_running_cancellable_activity,
            (),
            activity_opts(),
        );

        temporalio_sdk::workflows::select! {
            result = &mut activity_fut => {
                let value = result.map_err(|e| anyhow::anyhow!("{e}"))?;
                Ok(value)
            }
            reason = ctx.cancelled() => {
                activity_fut.cancel();

                let cleanup_result = ctx
                    .start_activity(
                        CancellationActivities::cleanup,
                        (),
                        ActivityOptions::start_to_close_timeout(Duration::from_secs(10)),
                    )
                    .await
                    .map_err(|e| anyhow::anyhow!("{e}"))?;

                Ok(format!("Cancelled (reason={reason}), {cleanup_result}"))
            }
        }
    }
}
```

## Terminate a Workflow Execution 

Terminating a Workflow forcefully stops Workflow Execution. This action resembles killing a process.

- The system records a `WorkflowExecutionTerminated` event in the Event History.
- The termination forcefully and immediately stops the Workflow Execution.
- The Workflow code gets no chance to handle termination.
- A Workflow Task doesn't get scheduled.

To terminate a Workflow Execution in Rust, use the `terminate` method on the client.

```rust
let handle = client.start_workflow(
    GreetingsWorkflow::run, 
    (), 
    WorkflowStartOptions::new("my-task-queue", "greetings-workflow-10").build()
).await?;

handle.terminate(WorkflowTerminateOptions::builder()
    .reason("Emergency shutdown")
    .build()
).await?;

```

## Reset a Workflow Execution 

Resetting a Workflow Execution terminates the current Workflow Execution and starts a new Workflow Execution from a
point you specify in its Event History. Use reset when a Workflow is blocked due to a non-deterministic error or other
issues that prevent it from completing.

When you reset a Workflow, the Event History up to the reset point is copied to the new Workflow Execution, and the
Workflow resumes from that point with the current code. Reset only works if you've fixed the underlying issue, such as
removing non-deterministic code. Any progress made after the reset point will be discarded. Provide a reason when
resetting, as it will be recorded in the Event History.

**Web UI**

1. Navigate to the Workflow Execution details page,
2. Click the **Reset** button in the top right dropdown menu,
3. Select the Event ID to reset to,
4. Provide a reason for the reset,
5. Confirm the reset.

The Web UI shows available reset points and creates a link to the new Workflow Execution after the reset completes.

**Temporal CLI**

Use the `temporal workflow reset` command to reset a Workflow Execution:

```bash
temporal workflow reset \
    --workflow-id <workflow-id> \
    --event-id <event-id> \
    --reason "Reason for reset"
```

For example:

```bash
temporal workflow reset \
    --workflow-id my-background-check \
    --event-id 4 \
    --reason "Fixed non-deterministic code"
```

By default, the command resets the latest Workflow Execution in the `default` Namespace. Use `--run-id` to reset a
specific run. Use `--namespace` to specify a different Namespace:

```bash
temporal workflow reset \
    --workflow-id my-background-check \
    --event-id 4 \
    --reason "Fixed non-deterministic code" \
    --namespace my-namespace \
    --tls-cert-path /path/to/cert.pem \
    --tls-key-path /path/to/key.pem
```

Monitor the new Workflow Execution after resetting to ensure it completes successfully.