Fix invalidateLater memory leak

[wch]

Closes #2267.

It looks like this particular leak was introduced by #2022.

In this test app, it redraws the plot and checks the memory used once per second.

Before this PR, the memory increases by about 7kB each iteration; after this PR, it does not increase at all (after the first few iterations).

library(shiny)
library(pryr)

ui <- fluidPage(
  plotOutput("hist1"),
  verbatimTextOutput("Memory")
)

server <- function(input, output, session) {
  i <- 0
  last_mem <- mem_used()

  output$hist1 <- renderPlot({
    invalidateLater(1000)
    plot(c(1:100))
  })
    
  output$Memory <- renderText({
    invalidateLater(1000)
    cur_mem <- mem_used()
    on.exit({
      i <<- i + 1
      last_mem <<- cur_mem
    })
    paste0(
      "Iteration:    ", i, "\n",
      "Memory usage: ", cur_mem, "\n",
      "Increase:     ", cur_mem - last_mem
    )
  })
}

shinyApp(ui,server)

Screenshot of before:

And after:

[ramindehghanpoor]

@wch Sorry, I'm not a professional. I'm trying your test app, and still, the memory usage is increasing. I reinstalled the development version of shiny from Github. Should I reinstall anything else to fix the problem?

[wch]

@ramindehghanpoor You need to install the branch in this pull request:

devtools::install_github("rstudio/shiny#2555")

[ramindehghanpoor]

@wch Thank you. It worked on my computer. Can I install the branch in this pull request and use this good version for our company website as well? We are using DigitalOcean server.

[wch]

You could, but this is a development branch of shiny and has not been tested as extensively as the current CRAN version of shiny, so it's possible you'll encounter bugs with it.

[yishan-guo]

@wch Sorry when I tryed devtools::install_github("#2555"), I got the error

devtools::install_github("#2555")
Error: Failed to install 'unknown package' from GitHub:
HTTP error 404.
No commit found for the ref wch-fix-invalidatelater-leak

Did you spell the repo owner (rstudio) and repo name (shiny) correctly?

• If spelling is correct, check that you have the required permissions to access the repo.

any idea why?

[wch]

This branch has been merged into master, so all you need to do now is this:

devtools::install_github("rstudio/shiny")