Running R code at predefined time (purely in R, no task manager / cron jobs)

I am trying to write a loop that allows running R code at a prespecified time.

This is typically done using task manager/taskscheduleR in windows. But for this particular task, I need to perform it purely on r as i will transfer it into a small shiny app. I sent this question here for the shiny part of it (Run shiny events at specified system times ), for now I need to make sure I have the appropriate code in R, then will work on shiny as next step.

this 2012 post ( I want to run a R code at a specific time ), mentioned a method I tried below but it did not work. It is supposed to print "It's time!" and opens the R project webpage 10 seconds after code is run.

time_to_run =  Sys.time()+10 #this defines the "target time", in this case, is 10 seconds later
while(TRUE) {
 
  if(Sys.time() == time_to_run) {
    print("It's time!")
    browseURL("https://www.r-project.org")
  }}

I also tried using repeat loop, but again without adequate response:

time_to_run =  Sys.time()+10
repeat {
  if(Sys.time() == time_to_run) {
    print("it's time!")
    browseURL("https://www.r-project.org")
 
  }
 
}

Any suggestions why this is not working?

thanks in advance.

Update:

Thanks to the comment below from Jon Spring, I leant how to compare Sys.time() after rounding to seconds.

what I do not understand now is: if I do not add break to the repeat loop, the code keeps opening the webpage endless number of times (if you try it, the computer may freeze, or you make have to restart r). isn't it supposed to run the code (ie open the webpage) only once when the condition is met and the two time points are equal? is there a way to make sure this happens?

thank you

library(lubridate)

time_to_run =  Sys.time()+5

 
repeat {
  if(round_date(Sys.time(),  unit = "second") == round_date(time_to_run,  unit = "second")) {
    print("it's time!")
    browseURL("https://www.r-project.org")
    break
  }
 
}

This is the final code I used and it is working, posting in case someone needs it. there are probably better ways to do the same task (eg shiny) but for this one I needed use in r

library(lubridate)

time_to_run =  Sys.time()+61

time_to_run = as.character(format(time_to_run, "%H:%M"))
 
repeat {
  noww = as.character(format(Sys.time(), "%H:%M"))
  
  print(noww)
  
  Sys.sleep(1)
  
  if(time_to_run == noww) {
    print("it's time!")
    browseURL("https://www.r-project.org")
    break
  }
 
}

Solution

Don't do busy-loops. Use Sys.sleep:

Sys.sleep(10)
print("it's time!")
browseURL("https://www.r-project.org")

If you want to run at a set time, rather than a set delay:

at_time <- Sys.time() + 3600  # 1 hour from now, or whenever

Sys.sleep(as.numeric(at_time - Sys.time())/1000)
print("it's time!")
browseURL("https://www.r-project.org")