Event source helpers

New to the concept? See Tools — Pool first.

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

Cancel and close in concurrent tasks:

• Pool closed — blocked callers wake with error.Closed.
• Task canceled — the operation returns error.Canceled.

When a handle becomes available, the Master can react. This is the job-pool pattern:

• Worker returns a handle.
• Master is notified.
• Master submits new work.

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Pool.Result

// nested in Pool
pub const Result = union(enum) {
    item: ItemHandle,
    closed: void,
    timeout: void,
    canceled: void,
    not_created: 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 pool no longer holds it.

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getWaitResult

pub fn getWaitResult(pl: *Pool, tag: *const anyopaque, timeout_ns: ?u64) Pool.Result

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

• Primary building block for Select integration:

  try select.concurrent(.pool, pool.getWaitResult, .{pl, TAG, null});
  

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

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get_wait_future

pub fn get_wait_future(self: *Pool, tag: *const anyopaque, timeout_ns: ?u64) ConcurrentError!Io.Future(Pool.Result)

• Thin wrapper: return p.*.io.concurrent(getWaitResult, .{pl, tag, 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 pool remains open.
• Closing is the Master's responsibility.

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