Handle and completion model

• Context exposes one handle per spawned context.
• Default construction and INIT create an invalid handle.
• spawn returns a valid handle.
• done? becomes TRUE only after the referenced context stores its completion state.
• cancel only requests cancellation and returns immediately.
• wait and get observe the same completion point.
• When the declared output schema is not (), the handle retains the stored completion value until destruction.
• Destroying a valid context waits for completion, releases the spawned context state, and destroys any retained non-Meta output storage.

Methods

• INIT
• valid?
• done?
• cancel
• wait
• get

Output mapping

• The declared output schema is selected by the out argument of spawn.
• The callable output is required to match that declared output schema.
• When the declared output schema is (), get produces no value.
• When the declared output schema is Meta, get returns that stored Meta object directly.
• Otherwise get returns one outputSchema Ref to the stored output.
• get leaves the handle valid.

Waiting and cancellation semantics

• If the current context is already canceled when wait or get begins, cancellation is first requested for the target context and waiting then continues until completion.
• If the current context is not canceled when wait or get begins, later cancellation of the current context requests cancellation of the target context.
• cancel only requests cancellation.
• After the target context becomes done, repeated wait and get calls return without additional suspension.

Examples

Initial state

"sync/Context" use
"control" use

{} Int32 {} [
  context: () Context;
  context.valid? printStack _:;
  0
] "main" exportFunction

Expected Output

FALSE

done? and get

"sync/Context" use
"sync/sync" use
"String" use
"control" use

{} Int32 {} [
  context: [2] Int32 spawn;
  context.done? [
    ("done" LF) printList
  ] [
    ("waiting" LF) printList
  ] if
  yield
  context.done? [
    ("done" LF) printList
  ] [
    ("waiting" LF) printList
  ] if
  value: @context.get;
  value isRef [
    ("ref" LF) printList
  ] [
    ("not-ref" LF) printList
  ] if
  drop
  ("value=" @value new LF) printList
  0
] "main" exportFunction

Expected Output

waiting
done
ref
value=2

Cancellation request and get

"sync/Context" use
"sync/sync" use
"control" use

{} Int32 {} [
  context: [10.0r64 sleepFor canceled?] FALSE spawn;
  @context.cancel
  result: @context.get;
  @result printStack _:;
  0
] "main" exportFunction

Expected Output

TRUE

See also

• sync/sync: Cross-platform scheduling, sleep, time, IPv4 formatting, and TCP helpers.
• sync/ContextGroup: Group of spawned contexts with shared waiting and cancellation.
• sync/Event: Persistent event state with clear, set, wait, wake, and wakeOne.
• windows/dispatcher: Windows completion-port dispatcher and callback posting helpers.