# Activity execution - PHP SDK

> Shows how to perform Activity execution with the PHP SDK

## How to start an Activity Execution 

Calls to spawn [Activity Executions](/activity-execution) are written within a [Workflow Definition](/workflow-definition).
The call to spawn an Activity Execution generates the [ScheduleActivityTask](/references/commands#scheduleactivitytask) Command.
This results in the set of three [Activity Task](/tasks#activity-task) related Events ([ActivityTaskScheduled](/references/events#activitytaskscheduled), [ActivityTaskStarted](/references/events#activitytaskstarted), and ActivityTask[Closed]) in your Workflow Execution Event History.

A single instance of the Activities implementation is shared across multiple simultaneous Activity invocations.
Activity implementation code should be _idempotent_.

The values passed to Activities through invocation parameters or returned through a result value are recorded in the Execution history.
The entire Execution history is transferred from the Temporal service to Workflow Workers when a Workflow state needs to recover.
A large Execution history can thus adversely impact the performance of your Workflow.

Therefore, be mindful of the amount of data you transfer through Activity invocation parameters or Return Values.
Otherwise, no additional limitations exist on Activity implementations.

Activity implementation is an implementation of an Activity interface.
The following code example, uses a constructor that takes an Amazon S3 client and a local directory, and uploads a file to the S3 bucket.
Then, the code uses a function to download a file from the S3 bucket passing a bucket name, remote name, and local name as arguments.
Finally, it uses a function that takes a local file name as an argument and returns a string.

```php
// An implementation of an Activity interface.
class FileProcessingActivitiesImpl implements FileProcessingActivities {

    private S3Client $s3Client;

    private string $localDirectory;

    public function __construct(S3Client $s3Client, string $localDirectory) {
        $this->s3Client = $s3Client;
        $this->localDirectory = $localDirectory;
    }

    // Uploading a file to S3.
    public function upload(string $bucketName, string $localName, string $targetName): void
    {
        $this->s3Client->putObject(
            $bucketName,
            $targetName,
            fopen($this->localDirectory . $localName, 'rb+')
        );
    }

// Downloading a file from S3.
    public function download(
        string $bucketName,
        string $remoteName,
        string $localName
    ): void
    {
        $this->s3Client->downloadObject(
            $bucketName,
            $remoteName,
            fopen($this->localDirectory .$localName, 'wb+')
        );
    }

// A function that takes a local file name as an argument and returns a string.
    public function processFile(string $localName): string
    {
        // Implementation omitted for brevity.
        return compressFile($this->localDirectory . $localName);
    }

    public function deleteLocalFile(string $fileName): void
    {
        unlink($this->localDirectory . $fileName);
    }
}
```

### How to set the required Activity Timeouts 

Activity Execution semantics rely on several parameters.
The only required value that needs to be set is either a [Schedule-To-Close Timeout](/encyclopedia/detecting-activity-failures#schedule-to-close-timeout) or a [Start-To-Close Timeout](/encyclopedia/detecting-activity-failures#start-to-close-timeout).
These values are set in the Activity Options.

### How to get the results of an Activity Execution 

The call to spawn an [Activity Execution](/activity-execution) generates the [ScheduleActivityTask](/references/commands#scheduleactivitytask) Command and provides the Workflow with an Awaitable.
Workflow Executions can either block progress until the result is available through the Awaitable or continue progressing, making use of the result when it becomes available.

`Workflow::newActivityStub`returns a client-side stub an implements an Activity interface. The client-side stub can be used within the Workflow code. It takes the Activity's type and`ActivityOptions` as arguments.

Calling (via `yield`) a method on this interface invokes an Activity that implements this method.
An Activity invocation synchronously blocks until the Activity completes, fails, or times out.
Even if Activity Execution takes a few months, the Workflow code still sees it as a single synchronous invocation.
It doesn't matter what happens to the processes that host the Workflow.
The business logic code just sees a single method call.

```php
class GreetingWorkflow implements GreetingWorkflowInterface
{
    private $greetingActivity;

    public function __construct()
    {
        $this->greetingActivity = Workflow::newActivityStub(
            GreetingActivityInterface::class,
            ActivityOptions::new()->withStartToCloseTimeout(\DateInterval::createFromDateString('30 seconds'))
        );
    }

    public function greet(string $name): \Generator
    {
        // This is a blocking call that returns only after the activity has completed.
        return yield $this->greetingActivity->composeGreeting('Hello', $name);
    }
}
```

If different Activities need different options, like timeouts or a task queue, multiple client-side stubs can be created with different options.

```php
$greetingActivity = Workflow::newActivityStub(
    GreetingActivityInterface::class,
    ActivityOptions::new()->withStartToCloseTimeout(\DateInterval::createFromDateString('30 seconds'))
);

$greetingActivity = Workflow::newActivityStub(
    GreetingActivityInterface::class,
    ActivityOptions::new()->withStartToCloseTimeout(\DateInterval::createFromDateString('30 minutes'))
);
```