Question

我从R Shiny Gallery获取此代码：http://shiny.rstudio.com/gallery/reactive-poll-and-file-reader.html

function(input, output, session) {

  # Create a random name for the log file
  logfilename <- paste0('logfile',
                        floor(runif(1, 1e+05, 1e+06 - 1)),
                        '.txt')


  # ============================================================
  # This part of the code writes to the log file every second.
  # Writing to the file could be done by an external process.
  # In this example, we'll write to the file from inside the app.
  logwriter <- observe({
    # Invalidate this observer every second (1000 milliseconds)
    invalidateLater(1000, session)

    # Clear log file if more than 10 entries
    if (file.exists(logfilename) &&
        length(readLines(logfilename)) > 10) {
      unlink(logfilename)
    }

    # Add an entry to the log file
    cat(as.character(Sys.time()), '\n', file = logfilename,
        append = TRUE)
  })

  # When the client ends the session, suspend the observer and
  # remove the log file.
  session$onSessionEnded(function() {
    logwriter$suspend()
    unlink(logfilename)
  })

  # ============================================================
  # This part of the code monitors the file for changes once per
  # 0.5 second (500 milliseconds).
  fileReaderData <- reactiveFileReader(500, session,
                                       logfilename, readLines)

  output$fileReaderText <- renderText({
    # Read the text, and make it a consistent number of lines so
    # that the output box doesn't grow in height.
    text <- fileReaderData()
    length(text) <- 14
    text[is.na(text)] <- ""
    paste(text, collapse = '\n')
  })


  # ============================================================
  # This part of the code monitors the file for changes once
  # every four seconds.

  pollData <- reactivePoll(4000, session,
    # This function returns the time that the logfile was last
    # modified
    checkFunc = function() {
      if (file.exists(logfilename))
        file.info(logfilename)$mtime[1]
      else
        ""
    },
    # This function returns the content of the logfile
    valueFunc = function() {
      readLines(logfilename)
    }
  )

  output$pollText <- renderText({
    # Read the text, and make it a consistent number of lines so
    # that the output box doesn't grow in height.
    text <- pollData()
    length(text) <- 14
    text[is.na(text)] <- ""
    paste(text, collapse = '\n')
  })
}

如果仔细查看上面的代码，您会看到以下代码：

# When the client ends the session, suspend the observer and
  # remove the log file.
  session$onSessionEnded(function() {
    logwriter$suspend()
    unlink(logfilename)
  })

我想在我的闪亮应用程序中调整该代码，以便将我的MySQL服务器与我的闪亮应用程序断开连接。像这样：

session$onSessionEnded(function() {
        dbDisconnect(con)
      })

我想这样做以确保此警告消息：“无法连接到数据库：连接太多”

是否可以确保为其他用户释放连接？（我的应用程序出现问题，因为有很多用户打开并且没有断开连接，在服务器上没有可用的位置。）

使用session $ onsessionend断开rshiny应用程序与mysql服务器的连接

0 个答案: