svTaskCallbackManager {svKomodo}

Create task callbacks that are evaluated both from R and socket/http server

Description

svTaskCallbackManager() is a copy of taskCallbackManager() in R base package, as of version 4.0.5 of R. Two important differences: (1) the top task created is named SV-taskCallbackManager instead of R-taskCallbackManager, and its tasks are executed after each top-level task in R console, or after execution of non-hidden R code from the socket or http server (take care: only once per set of code, no matter the number of top-level task in the R code send by the client in the second case). All taskCallbacks defined by addTaskCallback() or taskCallbackManager$add() from R base package are not executed when code is invoked from the R socket or http server!

Usage

svTaskCallbackManager(handlers = list(), registered = FALSE, verbose = FALSE)

Arguments

handlers

this can be a list of callbacks in which each element is a list with an element named f which is a callback function, and an optional element named data which is the 5-th argument to be supplied to the callback when it is invoked. Typically this argument is not specified, and one uses add to register callbacks after the manager is created.

registered

a logical value indicating whether the evaluate function has already been registered with the internal task callback mechanism. This is usually FALSE and the first time a callback is added via the add function, the evaluate function is automatically registered. One can control when the function is registered by specifying TRUE for this argument and calling addTaskCallback() manually.

verbose

a logical value, which if TRUE, causes information to be printed to the console about certain activities this dispatch manager performs. This is useful for debugging callbacks and the handler itself.

Value

See ?taskCallbackManager for both the returned object and how to use it.

Author(s)

Slightly modified from the original R core team's function by Ph. Grosjean [e-mail]

See Also

taskCallbackManager()

Examples

# create a task callback manager
cbman <- svTaskCallbackManager()
# Add a function to activate after each code evaluation in R
cbman$add(function(expr, value, ok, visible) {
  cat("Hi from the callback manager!\n")
  return(TRUE)
  }, name = "exampleHandler")
# Just issue a command and see the callback function activated
1 + 1
# List defined callbacks
cbman$callbacks()
# Remove the callback we just defined
cbman$remove("exampleHandler")
1 + 1
# Remove the task callback manager (base R function)
removeTaskCallback("SV-taskCallbackManager")