Event model

• A newly constructed Event starts with stored state FALSE.
• INIT and clear set the stored state to FALSE.
• set stores TRUE and wakes every currently waiting context.
• While the stored state is TRUE, later wait calls return immediately until clear.
• wake and wakeOne release only current waiters and do not change the stored state.
• wait returns no status or result value; after resumption, get exposes the stored state separately.
• An Event owns its stored state and waiter queue. Destroying an Event with waiting contexts is invalid.

Event

• INIT
• get
• clear
• set
• wait
• wake
• wakeOne

Methods

Waiting and cancellation semantics

• If the current context is already canceled when wait begins, wait returns immediately while the stored state remains unchanged.
• If cancellation happens while the context is already waiting, the context is resumed while the stored state remains unchanged.
• wake and wakeOne affect only contexts that are already waiting at that moment.
• wakeOne releases the oldest currently waiting context.
• No wake is remembered for later waiters.

Examples

set remembers the state

"sync/Event" use
"sync/sync" use
"String" use
"control" use

{} Int32 {} [
  event: Event;
  context: {event: @event; CALL: [
    @event.wait
    ("released" LF) printList
  ];} () spawn;
  @event.set
  yield
  context.done? [
    ("done" LF) printList
  ] [
    ("waiting" LF) printList
  ] if
  @context.wait
  event.get [
    ("TRUE" LF) printList
  ] [
    ("FALSE" LF) printList
  ] if
  0
] "main" exportFunction

Expected Output

released
done
TRUE

wakeOne without setting the state

"sync/Event" use
"sync/sync" use
"String" use
"control" use

{} Int32 {} [
  event: Event;
  context: {event: @event; CALL: [
    @event.wait
  ];} () spawn;
  yield
  @event.wakeOne
  @context.wait
  event.get [
    ("TRUE" LF) printList
  ] [
    ("FALSE" LF) printList
  ] if
  0
] "main" exportFunction

Expected Output

FALSE

clear restores blocking

"sync/Event" use
"sync/sync" use
"String" use
"control" use

{} Int32 {} [
  event: Event;
  @event.set
  @event.clear
  context: {event: @event; CALL: [
    @event.wait
    ("released" LF) printList
  ];} () spawn;
  yield
  context.done? [
    ("done" LF) printList
  ] [
    ("waiting" LF) printList
  ] if
  @event.wakeOne
  @context.wait
  0
] "main" exportFunction

Expected Output

waiting
released

See also

• sync/Signal: Wait queue with wake and wakeOne operations.
• sync/Context: Spawned context handle with waiting, output retrieval, and cancellation.
• sync/sync: Cross-platform scheduling, sleep, time, IPv4 formatting, and TCP helpers.