# task_all

## Function

Waits for a set of background tasks to complete and returns the success result of each task in the order entered. `task_all(tasks)` is a synchronous combination waiting function and will not cancel unfinished tasks.

## Syntax

```bt
values = task_all(tasks)
```

## Parameters

| Parameters | Type | Required | Default value | Description |
| ------ | ------ | ------ | ------ | ------ |
| tasks | Array<Task> | Yes | None | Array of Tasks to wait for. |

## Return value

| Type | Description |
| ------ | ------ |
| Array | When all tasks are successful, the result array is returned in the input order; an empty array returns `[]`. |

If any task fails `throw` or fails normally, `task_all()` waits for all tasks in the input to complete, then selects the first non-successful result in the order of input: `throw` will rethrow, and a normal failure returns a runtime error.

## Example

```bt
t1 = task(fn() {
    return 1
})

t2 = task(fn() {
    return 2
})

values = task_all([t1, t2])

// Output: [1,2]
print json(values)
```

```bt
slow = task(fn() {
    sleep(100)
    return 'slow'
})

fast = task(fn() {
    return 'fast'
})

values = task_all([slow, fast])

// Output: ["slow","fast"]
print json(values)
```

## Notes

- The parameter must be an array, and all array elements must be Task.
- `task_all([])` returns the empty array `[]`.
- Tasks are already executed concurrently when they are created. `task_all()` Waiting for results in the order of input will not turn task execution into serial.
- `task_all()` blocks the current execution flow; should be used with caution in web request hot paths.
- Still running tasks will not be forced to be canceled when other tasks fail.