R Threads - Experimental Support

Design loosely follows Python's Global Interpreter Lock.

Check this out:

• start a new thread and execute a R function in its own interpreter
• switch between threads on specific function calls, e.g. thread_join(), thread_print(), thread_sleep()
• finish thread execution
• keep track of R_PPStackTop

Missing:

• run an arbitrary C function outside of the Global Interpreter Lock
• synchronize memory allocation

Example: Computing a Sum

Here we verify low-level performance by computing the same sum in one thread (the standard sum() function) or in 4 threads via thread_sum(). We need to use a specialized function because sum() allocates memory which needs to be synchronized (but thread cannot do that yet).

library(thread)
run_c_computing_example()

Sum is the same, but time when using threads much shorter.

generating data
starting threads
main: going to join all threads
thread 1 computing from 0 to 249999999 
thread 2 computing from 2.5e+08 to 499999999 
thread 3 computing from 5e+08 to 749999999 
thread 4 computing from 7.5e+08 to 999999999 
main: going to claim results
[1] 5e+17
[1] 5e+17
   user  system elapsed 
  1.512   0.000   0.394 
   user  system elapsed 
  0.992   0.000   0.992 

Example: Printing

Here we present how one can implement IO threads.

library(thread)
 
thread_runner <- function (data) {
  thread_print(paste("thread", data, "starting\n"))
  for (i in 1:10) {
    timeout <- as.integer(abs(rnorm(1, 500, 1000)))
    thread_print(paste("thread", data, "iteration", i,
                       "sleeping for", timeout, "\n"))
    thread_sleep(timeout)
  }
  thread_print(paste("thread", data, "exiting\n"))
}
  
message("starting the first thread")
thread1 <- new_thread(thread_runner, 1)
print(ls(threads))
  
message("starting the second thread")
thread2 <- new_thread(thread_runner, 2)
print(ls(threads))
  
message("going to join() both threads")
thread_join(thread1)
thread_join(thread2)

Below you can see that output from both threads is interleaved due to randomized timeout.

starting the first thread
[1] "thread_140737231587072"
starting the second thread
[1] "thread_140737223194368" "thread_140737231587072"
going to join() both threads
thread 1 starting
thread 1 iteration 1 sleeping for 144 
thread 2 starting
thread 2 iteration 1 sleeping for 587 
thread 1 iteration 2 sleeping for 761 
thread 2 iteration 2 sleeping for 1327 
thread 1 iteration 3 sleeping for 360 
thread 1 iteration 4 sleeping for 1802 
thread 2 iteration 3 sleeping for 704 
thread 2 iteration 4 sleeping for 463 
thread 1 iteration 5 sleeping for 368 
thread 2 iteration 5 sleeping for 977 
thread 1 iteration 6 sleeping for 261 
thread 1 iteration 7 sleeping for 323 
thread 1 iteration 8 sleeping for 571 
thread 2 iteration 6 sleeping for 509 
thread 2 iteration 7 sleeping for 2521 
thread 1 iteration 9 sleeping for 298 
thread 1 iteration 10 sleeping for 394 
thread 1 exiting
thread 2 iteration 8 sleeping for 966 
thread 2 iteration 9 sleeping for 533 
thread 2 iteration 10 sleeping for 1795 
thread 2 exiting