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 system
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.
p <- process$new(command = NULL, args, stdin = NULL, stdout = NULL, stderr = NULL, connections = list(), poll_connection = NULL, env = NULL, cleanup = TRUE, cleanup_tree = FALSE, wd = NULL, echo_cmd = FALSE, supervise = FALSE, windows_verbatim_args = FALSE, windows_hide_window = FALSE, encoding = "", post_process = NULL)p$is_alive() p$signal(signal) p$interrupt() p$kill(grace = 0.1, close_connections = TRUE) p$kill_tree(grace = 0.1, close_connections = TRUE) p$wait(timeout = -1) p$get_pid() p$get_exit_status() p$get_start_time()
p$read_output(n = -1) p$read_error(n = -1) p$read_output_lines(n = -1) p$read_error_lines(n = -1) p$has_input_connection() p$has_output_connection() p$has_error_connection() p$has_poll_connection() p$get_input_connection() p$get_output_connection() p$get_error_connection() p$get_poll_connection() p$is_incomplete_output() p$is_incomplete_error() p$read_all_output() p$read_all_error() p$read_all_output_lines() p$read_all_error_lines() p$write_input(str, sep = "\n") p$get_input_file() p$get_output_file() p$get_error_file()
p$poll_io(timeout)
p$get_result()
p$as_ps_handle() p$get_name() p$get_exe() p$get_cmdline() p$get_status() p$get_username() p$get_wd() p$get_cpu_times() p$get_memory_info() p$suspend() p$resume()
format(p) print(p)
p
: process
object.
command
: Character scalar, the command to run.
Note that this argument is not passed to a shell, so no
tilde-expansion or variable substitution is performed on it.
It should not be quoted with base::shQuote()
. See
base::normalizePath()
for tilde-expansion.
args
: Character vector, arguments to the command. They will be
used as is, without a shell. They don't need to be escaped.
stdin
: What to do with the standard input. Possible values:
NULL
: set to the null device, i.e. no standard input is
provided; a string, supply the specified string as standard input;
"|"
: create a (writeable) connection for stdin.
stdout
: What to do with the standard output. Possible values:
NULL
: discard it; a string, redirect it to this file;
"|"
: create a connection for it.
stderr
: What to do with the standard error. Possible values:
NULL
: discard it; a string, redirect it to this file;
"|"
: create a connection for it; "2>&1"
: redirect it to the
same connection (i.e. pipe or file) as stdout
. "2>&1"
is a
way to keep standard output and error correctly interleaved.
connections
: A list of connections to pass to the child process.
This is an experimental feature currently.
poll_connection
: Whether to create an extra connection to the process
that allows polling, even if the standard input and standard output
are not pipes. If this is NULL
(the default), then this connection
will be only created if standard output and standard error are not
pipes, and connections
is an empty list. If the poll connection is
created, you can query it via p$get_poll_connection()
and it is
also included in the response to p$poll_io()
and poll()
. The
numeric file descriptor of the poll connection comes right after
stderr
(2), and the connections listed in connections
.
env
: Environment variables of the child process. If NULL
, the
parent's environment is inherited. On Windows, many programs cannot
function correctly if some environment variables are not set, so we
always set HOMEDRIVE
, HOMEPATH
, LOGONSERVER
, PATH
,
SYSTEMDRIVE
, SYSTEMROOT
, TEMP
, USERDOMAIN
, USERNAME
,
USERPROFILE
and WINDIR
.
cleanup
: Whether to kill the process when the process
object is
garbage collected.
cleanup_tree
: Whether to kill the process and its child process tree
when the process
object is garbage collected.
wd
: working directory of the process. It must exist. If NULL
, then
the current working directory is used.
echo_cmd
: Whether to print the command to the screen before
running it.
supervise
: Whether to register the process with a supervisor.
If TRUE
, the supervisor will ensure that the process is
killed when the R process exits.
windows_verbatim_args
: Whether to omit quoting the arguments
on Windows. It is ignored on other platforms.
windows_hide_window
: Whether to hide the application's window
on Windows. It is ignored on other platforms.
signal
: An integer scalar, the id of the signal to send to
the process. See tools::pskill()
for the list of signals.
grace
: Currently not used.
close_connections
: Whether to close standard input, standard output,
standard error connections and the poll connection, after killing
the process.
timeout
: Timeout in milliseconds, for the wait or the I/O
polling.
n
: Number of characters or lines to read.
str
: Character or raw vector to write to the standard input of the
process. If a character vector with a marked encoding, it will be
converted to encoding
.
sep
: Separator to add between str
elements if it is a character
vector. It is ignored if str
is a raw vector.
encoding
: The encoding to assume for stdin
, stdout
and
stderr
. By default the encoding of the current locale is
used. Note that processx
always reencodes the output of the
stdout
and stderr
streams in UTF-8 currently.
If you want to read them without any conversion, on all platforms,
specify "UTF-8"
as encoding.
post_process
: An optional function to run when the process has
finished. Currently it only runs if $get_result()
is called.
It is only run once.
The poll_io()
function polls the standard output and standard
error connections of a process, with a timeout. If there is output
in either of them, or they are closed (e.g. because the process exits)
poll_io()
returns immediately.
In addition to polling a single process, the poll()
function
can poll the output of several processes, and returns as soon as any
of them has generated output (or exited).
processx kills processes that are not referenced any more (if cleanup
is set to TRUE
), or the whole subprocess tree (if cleanup_tree
is
also set to TRUE
).
The cleanup happens when the references of the processes object are
garbage collected. To clean up earlier, you can call the kill()
or
kill_tree()
method of the process(es), from an on.exit()
expression,
or an error handler:
process_manager <- function() { on.exit({ try(p1$kill(), silent = TRUE) try(p2$kill(), silent = TRUE) }, add = TRUE) p1 <- process$new("sleep", "3") p2 <- process$new("sleep", "10") p1$wait() p2$wait() } process_manager()
If you interrupt process_manager()
or an error happens then both p1
and p2
are cleaned up immediately. Their connections will also be
closed. The same happens at a regular exit.
$new()
starts a new process in the background, and then returns
immediately.
$is_alive()
checks if the process is alive. Returns a logical
scalar.
$signal()
sends a signal to the process. On Windows only the
SIGINT
, SIGTERM
and SIGKILL
signals are interpreted,
and the special 0 signal, The first three all kill the process. The 0
signal return TRUE
if the process is alive, and FALSE
otherwise. On Unix all signals are supported that the OS supports, and
the 0 signal as well.
$interrupt()
sends an interrupt to the process. On Unix this is a
SIGINT
signal, and it is usually equivalent to pressing CTRL+C at the
terminal prompt. On Windows, it is a CTRL+BREAK keypress. Applications
may catch these events. By default they will quit.
$kill()
kills the process. It also kills all of its child
processes, except if they have created a new process group (on Unix),
or job object (on Windows). It returns TRUE
if the process
was killed, and FALSE
if it was no killed (because it was
already finished/dead when processx
tried to kill it).
$kill_tree()
performs process tree cleanup, it kills the process
(if still alive), together with any child (or grandchild, etc.)
processes. It uses the ps package, so that needs to be installed,
and ps needs to support the current platform as well. Process tree
cleanup works by marking the process with an environment variable,
which is inherited in all child processes. This allows finding
descendents, even if they are orphaned, i.e. they are not connected
to the root of the tree cleanup in the process tree any more.
$kill_tree()
returns a named integer vector of the process ids that
were killed, the names are the names of the processes (e.g. "sleep"
,
"notepad.exe"
, "Rterm.exe"
, etc.).
$wait()
waits until the process finishes, or a timeout happens.
Note that if the process never finishes, and the timeout is infinite
(the default), then R will never regain control. It returns
the process itself, invisibly. In some rare cases, $wait()
might take
a bit longer than specified to time out. This happens on Unix, when
another package overwrites the processx SIGCHLD signal handler, after the
processx process has started. One such package is parallel, if used
with fork clusters, e.g. through parallel::mcparallel()
.
$get_pid()
returns the process id of the process.
$get_exit_status
returns the exit code of the process if it has
finished and NULL
otherwise. On Unix, in some rare cases, the exit
status might be NA
. This happens if another package (or R itself)
overwrites the processx SIGCHLD handler, after the processx process
has started. In these cases processx cannot determine the real exit
status of the process. One such package is parallel, if used with
fork clusters, e.g. through the parallel::mcparallel()
function.
$get_start_time()
returns the time when the process was
started.
$is_supervised()
returns whether the process is being tracked by
supervisor process.
$supervise()
if passed TRUE
, tells the supervisor to start
tracking the process. If FALSE
, tells the supervisor to stop
tracking the process. Note that even if the supervisor is disabled for a
process, if it was started with cleanup = TRUE
, the process will
still be killed when the object is garbage collected.
$read_output()
reads from the standard output connection of the
process. If the standard output connection was not requested, then
then it returns an error. It uses a non-blocking text connection. This
will work only if stdout="|"
was used. Otherwise, it will throw an
error.
$read_error()
is similar to $read_output
, but it reads
from the standard error stream.
$read_output_lines()
reads lines from standard output connection
of the process. If the standard output connection was not requested, then
then it returns an error. It uses a non-blocking text connection. This
will work only if stdout="|"
was used. Otherwise, it will throw an
error.
$read_error_lines()
is similar to $read_output_lines
, but
it reads from the standard error stream.
$has_input_connection()
return TRUE
if there is a connection
object for standard input; in other words, if stdout="|"
. It returns
FALSE
otherwise.
$has_output_connection()
returns TRUE
if there is a connection
object for standard output; in other words, if stdout="|"
. It returns
FALSE
otherwise.
$has_error_connection()
returns TRUE
if there is a connection
object for standard error; in other words, if stderr="|"
. It returns
FALSE
otherwise.
$has_poll_connection()
return TRUE
if there is a poll connection,
FALSE
otherwise.
$get_input_connection()
returns a connection object, to the
standard input stream of the process.
$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.
$get_poll_connetion()
returns the poll connection, if the process has
one.
$is_incomplete_output()
return FALSE
if the other end of
the standard output connection was closed (most probably because the
process exited). It return TRUE
otherwise.
$is_incomplete_error()
return FALSE
if the other end of
the standard error connection was closed (most probably because the
process exited). It return TRUE
otherwise.
$read_all_output()
waits for all standard output from the process.
It does not return until the process has finished.
Note that this process involves waiting for the process to finish,
polling for I/O and potentically several readLines()
calls.
It returns a character scalar. This will return content only if
stdout="|"
was used. Otherwise, it will throw an error.
$read_all_error()
waits for all standard error from the process.
It does not return until the process has finished.
Note that this process involves waiting for the process to finish,
polling for I/O and potentically several readLines()
calls.
It returns a character scalar. This will return content only if
stderr="|"
was used. Otherwise, it will throw an error.
$read_all_output_lines()
waits for all standard output lines
from a process. It does not return until the process has finished.
Note that this process involves waiting for the process to finish,
polling for I/O and potentically several readLines()
calls.
It returns a character vector. This will return content only if
stdout="|"
was used. Otherwise, it will throw an error.
$read_all_error_lines()
waits for all standard error lines from
a process. It does not return until the process has finished.
Note that this process involves waiting for the process to finish,
polling for I/O and potentically several readLines()
calls.
It returns a character vector. This will return content only if
stderr="|"
was used. Otherwise, it will throw an error.
$write_input()
writes the character vector (separated by sep
) to
the standard input of the process. It will be converted to the specified
encoding. This operation is non-blocking, and it will return, even if
the write fails (because the write buffer is full), or if it suceeds
partially (i.e. not the full string is written). It returns with a raw
vector, that contains the bytes that were not written. You can supply
this raw vector to $write_input()
again, until it is fully written,
and then the return value will be raw(0)
(invisibly).
$get_input_file()
if the stdin
argument was a filename,
this returns the absolute path to the file. If stdin
was "|"
or
NULL
, this simply returns that value.
$get_output_file()
if the stdout
argument was a filename,
this returns the absolute path to the file. If stdout
was "|"
or
NULL
, this simply returns that value.
$get_error_file()
if the stderr
argument was a filename,
this returns the absolute path to the file. If stderr
was "|"
or
NULL
, this simply returns that value.
$poll_io()
polls the process's connections for I/O. See more in
the Polling section, and see also the poll()
function
to poll on multiple processes.
$get_result()
returns the result of the post processesing function.
It can only be called once the process has finished. If the process has
no post-processing function, then NULL
is returned.
$as_ps_handle()
returns a ps::ps_handle object, corresponding to
the process. The following methods use the ps package on a ps_handle
object, created automatically:
p$get_name()
calls ps::ps_name()
to get the process name.
p$get_exe()
calls ps::ps_exe()
to get the path of the executable.
p$get_cmdline()
calls ps::ps_cmdline()
to get the command line.
p$get_status()
calls ps::ps_status()
to get the process status.
p$get_username()
calls ps::ps_username()
to get the username.
p$get_wd()
calls ps::ps_cwd()
to get the current working
directory.
p$get_cpu_times()
calls ps::ps_cpu_times()
to get CPU usage data.
p$get_memory_info()
calls ps::ps_memory_info()
to get memory usage
data.
p$suspend()
calls ps::ps_suspend()
to suspend the process.
p$resume()
calls ps::ps_resume()
to resume a suspended process.
format(p)
or p$format()
creates a string representation of the
process, usually for printing.
print(p)
or p$print()
shows some information about the
process on the screen, whether it is running and it's process id, etc.
# NOT RUN {
# CRAN does not like long-running examples
# }
# NOT RUN {
p <- process$new("sleep", "2")
p$is_alive()
p
p$kill()
p$is_alive()
p <- process$new("sleep", "2")
p$is_alive()
Sys.sleep(3)
p$is_alive()
# }
# NOT RUN {
# }
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