process

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External process

Managing external processes from R is not trivial, and this class aims to help with this deficiency. It is essentially a small wrapper around the pipe base R function, to return the process id of the started process, and set its standard output and error streams. The process id is then used to manage the process.

Usage

p <- process$new(command = NULL, args, commandline = NULL,
                 stdout = TRUE, stderr = TRUE, cleanup = TRUE) p$is_alive()
p$kill(grace = 0.1)
p$wait()
p$get_exit_status()
p$restart() p$read_output_lines(...)
p$read_error_lines(...)
p$can_read_output()
p$can_read_error()
p$is_eof_output()
p$is_eof_error()
p$get_output_connection()
p$get_error_connection() print(p)

Arguments

Details

$new() starts a new process, it uses pipe. R does not wait for the process to finish, but returns immediately. $is_alive() checks if the process is alive. Returns a logical scalar. $kill() kills the process. It also kills all of its child processes. First it sends the child processes a TERM signal, and then after a grace period a KILL signal. Then it does the same for the process itself. A killed process can be restarted using the restart method. It returns the process itself. $wait() waits until the process finishes. Note that if the process never finishes, then R will never regain control. It returns the process itself. $get_exit_code returns the exit code of the process if it has finished and wait was called on it. Otherwise it will return NULL. $restart() restarts a process. It returns the process itself. $read_output_lines() reads from standard output of the process. If the standard output was not requested, then it returns an error. It uses a non-blocking text connection. $read_error_lines() is similar to $read_output_lines, but it reads from the standard error stream. $can_read_output() checks if there is any standard output immediately available. $can_read_error() checks if there is any standard error immediately available. $is_eof_output() checks if the standard output stream has ended. This means that the process is finished and all output has been processed. $is_eof_error() checks if the standard error stream has ended. This means that the process is finished and all output has been processed. $get_output_connection() returns a connection object, to the standard output stream of the process. $get_error_conneciton() returns a connection object, to the standard error stream of the process. print(p) or p$print() shows some information about the process on the screen, whether it is running and it's process id, etc.

Aliases
  • process
Examples
# CRAN does not like long-running examples
## Not run: 
# p <- process$new("sleep", "2")
# p$is_alive()
# p
# p$kill()
# p$is_alive()
# 
# p$restart()
# p$is_alive()
# Sys.sleep(3)
# p$is_alive()
# ## End(Not run)

Documentation reproduced from package processx, version 1.0.0, License: MIT + file LICENSE

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