| tclTask {tcltk2} | R Documentation |
Tcl allows fo 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.
# Convenient tclTask objects management tclTaskSchedule(wait, expr, id = "task#", redo = FALSE) tclTaskRun(id) tclTaskGet(id = NULL, all = FALSE) tclTaskChange(id, expr, wait, redo) tclTaskDelete(id) # Low-level Tcl functions tclAfter(wait, fun) tclAfterCancel(task) tclAfterInfo(task = NULL)
wait |
Time in ms to delay the task (take care: approximative 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). |
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. |
all |
If id = NULL, all = TRUE indicate to list all tasks,
including hidden ones (with id starting with a dot). |
redo |
Should the task be rescheduled n times, indefinitely
(redo = TRUE) or not (redo = FALSE, default, or a value <=
0). |
task |
A Tcl task timer, or its name in Tcl (in the form of 'after#xxx'). |
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 ecxists, 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.
Philippe Grosjean
tclFun, addTaskCallback,
Sys.sleep
## Not run:
## 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)
## End(Not run)