\name{invalidateLater}
\alias{invalidateLater}
\title{Scheduled Invalidation}
\usage{
  invalidateLater(millis, session)
}
\arguments{
  \item{millis}{Approximate milliseconds to wait before
  invalidating the current reactive context.}

  \item{session}{A session object. This is needed to cancel
  any scheduled invalidations after a user has ended the
  session. If \code{NULL}, then this invalidation will not
  be tied to any session, and so it will still occur.}
}
\description{
  Schedules the current reactive context to be invalidated
  in the given number of milliseconds.
}
\details{
  If this is placed within an observer or reactive
  expression, that object will be invalidated (and
  re-execute) after the interval has passed. The
  re-execution will reset the invalidation flag, so in a
  typical use case, the object will keep re-executing and
  waiting for the specified interval. It's possible to stop
  this cycle by adding conditional logic that prevents the
  \code{invalidateLater} from being run.
}
\examples{
\dontrun{
shinyServer(function(input, output, session) {

  observe({
    # Re-execute this reactive expression after 1000 milliseconds
    invalidateLater(1000, session)

    # Do something each time this is invalidated.
    # The isolate() makes this observer _not_ get invalidated and re-executed
    # when input$n changes.
    print(paste("The value of input$n is", isolate(input$n)))
  })

  # Generate a new histogram at timed intervals, but not when
  # input$n changes.
  output$plot <- renderPlot({
    # Re-execute this reactive expression after 2000 milliseconds
    invalidateLater(2000, session)
    hist(isolate(input$n))
  })
})
}
}
\seealso{
  \code{\link{reactiveTimer}} is a slightly less safe
  alternative.
}