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.
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').
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 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.
Author(s)
Philippe Grosjean
See Also
tclFun, addTaskCallback,
Sys.sleep
Examples
## 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)