pool

Pool[A, E]: share scoped resources across fibers.

A pool acquires items with a scoped effect, lends them to fibers, and releases them all when the scope it was made in closes::

pool = yield from fx.Pool.make(connect, size=10)
rows = yield from pool.use(lambda conn: conn.query("..."))

• Pool.make(acquire, size=): a fixed number of items, acquired at once.
• Pool.make_with_ttl(acquire, min=, max=, time_to_live=): grows with demand up to max and shrinks back to min once items have been idle ("usage", the default) or alive ("creation") for the time to live.
• Pool.make_with_strategy: a custom Strategy resizes the pool.

concurrency lets each item serve several borrowers at once; the pool grows once usage / target_utilization exceeds what its items serve. get borrows until the current scope closes, use for as long as a function's effect runs; borrowers wait in line for a free item, and a failed acquisition fails the borrower that reaches it. invalidate retires an item once its last borrower returns it, reserve keeps an item from new borrowers for a scope.

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