Schedule and manage delayed tasks

Tcl allows for scheduling execution of code on the next event loop or after a given time (after Tcl command). tclTaskXxx() functions use it to schedule execution of R code with much control from within R (central management of scheduled tasks, possibility to define redoable tasks, use of S3 objects to keep track of tasks information. The tclAfterXxx() functions are low-level access to the Tcl after command.

tclAfter(wait, fun)

tclAfterCancel(task)

tclAfterInfo(task = NULL)

# S3 method for class 'tclTask'
print(x, ...)

tclTaskSchedule(wait, expr, id = "task#", redo = FALSE)

tclTaskRun(id)

tclTaskGet(id = NULL, all = FALSE)

tclTaskChange(id, expr, wait, redo)

tclTaskDelete(id)

Arguments

wait: Time in ms to delay the task (take care: approximate value, depends on when event loops are triggered). Using a value lower or equal to zero, the task is scheduled on the next event loop.
fun: Name of the R function to run (you may not supply arguments to this function, otherwise it is not scheduled properly; take care of scoping, since a copy of the function will be run from within Tcl).
task: A Tcl task timer, or its name in Tcl (in the form of 'after#xxx').
x: A 'tclTask' object.
...: Further argument to the print() method.
expr: An expression to run after 'wait'.
id: The R identifier of the task to schedule, if this id contains #, then, it is replaced by next available number, but you cannot schedule more than a thousand tasks with the same name (the system will give up well before, anyway). If NULL in tclTaskGet(), retrieve the list of all existing tasks.
redo: Should the task be rescheduled n times, indefinitely (redo = TRUE) or not (redo = FALSE, default, or a value <= 0).
all: If id = NULL, all = TRUE indicate to list all tasks, including hidden ones (with id starting with a dot).

Value

The tclAfterXxx() functions return a 'tclObj' with the result of the corresponding Tcl function. tclAfter() returns the created Tcl timer in this object. If 'task' does not exists, tclAfterInfo() returns NULL.

tclTaskGet() returns a 'tclTask' object, a list of such objects, or NULL if not found.

The four remaining tclTaskXxx() functions return invisibly TRUE if the process is done successfully, FALSE otherwise. tclTaskRun() forces running a task now, even if it is scheduled later.

Author

Philippe Grosjean

Examples

if (FALSE) { # \dontrun{
# These cannot be run by examples() but should be OK when pasted
# into an interactive R session with the tcltk package loaded

# Run just once, after 1 sec
test <- function () cat("==== Hello from Tcl! ====\n")
tclTaskSchedule(1000, test())
Sys.sleep(2)

# Run ten times a task with a specified id
test2 <- function () cat("==== Hello again from Tcl! ====\n")
tclTaskSchedule(1000, test2(), id = "test2", redo = 10)
Sys.sleep(1)

# Run a function with arguments (will be evaluated in global environment)
test3 <- function (txt) cat(txt, "\n")
msg <- "==== First message ===="
tclTaskSchedule(1000, test3(msg), id = "test3", redo = TRUE)
Sys.sleep(2)
msg <- "==== Second message ===="
Sys.sleep(2)

# Get info on pending tasks
tclTaskGet() # List all (non hidden) tasks
tclTaskGet("test2")
# List all active Tcl timers
tclAfterInfo()

# Change a task (run 'test3' only once more, after 60 sec)
tclTaskChange("test3", wait = 60000, redo = 1)
Sys.sleep(1)
# ... but don't wait so long and force running 'test3' right now
tclTaskRun("test3")

Sys.sleep(3)
# finally, delete all pending tasks
tclTaskDelete(NULL)
} # }

Arguments

Value

See also

Author

Examples