Futures

Futures

Asynchronous operation results. Futures are returned by funcs.async() and contract async calls.

Loading

Not a loadable module. Futures are created by async operations:

local funcs = require("funcs")
local future, err = funcs.async("app.compute:task", data)

Response Channel

Get channel for receiving result:

local ch = future:response()
local payload, ok = ch:receive()
if ok then
    local result = payload:data()
end

channel() is an alias for response().

Completion Check

Non-blocking check if future completed:

if future:is_complete() then
    local result, err = future:result()
end

Cancellation Check

Check if cancel() was called:

if future:is_canceled() then
    print("Operation was canceled")
end

Getting Result

Get cached result (non-blocking):

local val, err = future:result()

Returns:

• Not complete: nil, nil
• Canceled: nil, error (kind CANCELED)
• Error: nil, error
• Success: Payload, nil or table, nil (multiple payloads)

Getting Error

Get error if future failed:

local err, has_error = future:error()
if has_error then
    print("Failed:", err:message())
end

Returns: error, boolean

Canceling

Cancel async operation (best-effort):

future:cancel()

Operation may still complete if already in progress.

Timeout Pattern

local future = funcs.async("app.compute:slow", data)
local timeout = time.after("5s")

local r = channel.select {
    future:channel():case_receive(),
    timeout:case_receive()
}

if r.channel == timeout then
    future:cancel()
    return nil, errors.new("TIMEOUT", "Operation timed out")
end

return r.value:data()

First-to-Complete

local f1 = funcs.async("app.cache:get", key)
local f2 = funcs.async("app.db:get", key)

local r = channel.select {
    f1:channel():case_receive(),
    f2:channel():case_receive()
}

-- Cancel the slower one
if r.channel == f1:channel() then
    f2:cancel()
else
    f1:cancel()
end

return r.value:data()

Errors

Condition	Kind
Operation canceled	CANCELED
Async operation failed	varies