Create a pool of reusable objects

A generic pool class that holds objects. These can be fetched from the pool and released back to it at will, with very little computational cost. The pool should be created only once and closed when it is no longer needed, to prevent leaks.

Every usage of poolCreate() should always be paired with a call to poolClose() to avoid "leaking" resources. In shiny app, you should create the pool outside of the server function and close it on stop, i.e. onStop(function() pool::poolClose(pool)).

See dbPool() for an example of object pooling applied to DBI database connections.

Usage

poolCreate(
  factory,
  minSize = 1,
  maxSize = Inf,
  idleTimeout = 60,
  validationInterval = 60,
  state = NULL
)

poolClose(pool)

# S4 method for Pool
poolClose(pool)

Arguments

factory

A zero-argument function called to create the objects that the pool will hold (e.g. for DBI database connections, dbPool() uses a wrapper around DBI::dbConnect()).

minSize, maxSize

The minimum and maximum number of objects in the pool.

idleTimeout

Number of seconds to wait before destroying idle objects (i.e. objects available for checkout over and above minSize).

validationInterval

Number of seconds to wait between validating objects that are available for checkout. These objects are validated in the background to keep them alive.

To force objects to be validated on every checkout, set validationInterval = 0.

state

A pool public variable to be used by backend authors.

pool

A Pool object previously created with poolCreate