Contents

DiscardingTaskGroup

A discarding group that contains dynamically created child tasks.

Declaration

@frozen struct DiscardingTaskGroup

Overview

To create a discarding task group, call the withDiscardingTaskGroup(returning:body:) method.

Don’t use a task group from outside the task where you created it. In most cases, the Swift type system prevents a task group from escaping like that because adding a child task to a task group is a mutating operation, and mutation operations can’t be performed from a concurrent execution context like a child task.

Refer to TaskGroup documentation for detailed discussion of semantics shared between all task groups.

Discarding behavior

A discarding task group eagerly discards and releases its child tasks as soon as they complete. This allows for the efficient releasing of memory used by those tasks, which are not retained for future next() calls, as would be the case with a TaskGroup.

Cancellation behavior

A discarding task group becomes canceled in one of the following ways:

  • when cancelAll() is invoked on it,

  • when the Task running this task group is canceled.

Since a DiscardingTaskGroup is a structured concurrency primitive, cancellation is automatically propagated through all of its child-tasks (and their child tasks).

A canceled task group can still keep adding tasks, however they will start being immediately canceled, and may act accordingly to this. To avoid adding new tasks to an already canceled task group, use addTaskUnlessCancelled(priority:body:) rather than the plain addTask(priority:body:) which adds tasks unconditionally.

For information about the language-level concurrency model that DiscardingTaskGroup is part of, see Concurrency in The Swift Programming Language.

Topics

Instance Properties

Instance Methods

See Also

Tasks