How to... Io — Select, Group, Future

Event loops over multiple sources, cancellation, and awaiting futures
directly instead of through a mailbox.

• Two mailboxes + timer in Select
• Timer cancel → close → walk remaining
• Cancel reports, Master decides
• Multiple event source types in one Select
• Cancel → Master close → pool.put_all
• Graceful shutdown with in-flight items
• Mailbox receive as Select event source
• Select direct queue push
• Select mailbox close propagation
• Select cancel propagation
• Pool get_wait as Select event source
• Job pool pattern
• Mixed mailbox + pool event sources in Select
• receive_future awaited directly
• get_wait_future awaited directly
• receive_future with timeout
• ConcurrencyUnavailable on single-threaded
• Pool + Future: simple worker
• Pool + Select: job scheduler
• Pool + Group: worker pool
• Pool + Select + Network
• When to add Mailbox