Event source helpers

New to the concept? See Tools — Mailbox first.

Mailbox as event source for Io.Select and Io.Future.

Cancel and close in concurrent tasks:

• Mailbox closed — blocked receivers wake with error.Closed.
• Task canceled — the operation returns error.Canceled.

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Mbox.Result

// nested in Mbox
pub const Result = union(enum) {
    item: ItemHandle,
    closed: void,
    timeout: void,
    canceled: void,
    wakeup: void,
};

• The handle is inside the result, not behind a pointer. No *Slot is shared across threads.
• When you get .item, the handle is yours. The mailbox no longer holds it.

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receiveResult

pub fn receiveResult(mbx: *Mbox, timeout_ns: ?u64) Mbox.Result

• Blocking function. No error return — maps all outcomes to Mbox.Result variants.

• Primary building block for Select integration:

  try select.concurrent(.inbox, mailbox.receiveResult, .{mbx, null});
  

• Also usable with io.concurrent or group.concurrent.

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receive_future

pub fn receive_future(self: *Mbox, timeout_ns: ?u64) ConcurrentError!Io.Future(Mbox.Result)

• Thin wrapper: return mbx.*.io.concurrent(receiveResult, .{mbx, timeout_ns}).
• No heap allocation — args copied by the runtime before concurrent returns.
• Returns a Future for direct await or Io.Group use.
• Returns error.ConcurrencyUnavailable on single-threaded backends.

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Cancel behavior

• On error.Canceled, returns .canceled — the mailbox remains open.
• Closing is the Master's responsibility.

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When to use

select.concurrent pattern (primary):

try select.concurrent(.inbox, mailbox.receiveResult, .{mbx, null});
const event = try select.await();
switch (event) {
    .inbox => |r| switch (r) { ... },
    ...
}

receive_future pattern (direct await or Group):

const fut = try mbx.receive_future(null);
const result = try fut.await(io);

Bridging to external Io: one Io.Select loop combines mailbox, timers, sockets, pool availability.

• Matryoshka sources use receiveResult / getWaitResult via select.concurrent.
• External sources use their own blocking functions via select.concurrent.
• Direct push: select.queue.putOneUncancelable(io, value) for immediate events.

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