processx: poll – R documentation

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poll

Poll for process I/O or termination

Description

Wait until one of the specified connections or processes produce standard output or error, terminates, or a timeout occurs.

Usage

poll(processes, ms)

Arguments

`processes`	A list of connection objects or`process` objects to wait on. (They can be mixed as well.) If this is a named list, then the returned list will have the same names. This simplifies the identification of the processes.
`ms`	Integer scalar, a timeout for the polling, in milliseconds. Supply -1 for an infitite timeout, and 0 for not waiting at all.

Value

A list of character vectors of length one or three. There is one list element for each connection/process, in the same order as in the input list. For connections the result is a single string scalar. For processes the character vectors' elements are named output, error and process. Possible values for each individual result are: nopipe, ready, timeout, closed, silent. See details about these below. process refers to the poll connection, see the poll_connection argument of the process initializer.

Explanation of the return values

nopipe means that the stdout or stderr from this process was not captured.
ready means that the connection or the stdout or stderr from this process are ready to read from. Note that end-of-file on these outputs also triggers ready.
timeout': the connections or processes are not ready to read from and a timeout happened.
closed: the connection was already closed, before the polling started.
silent: the connection is not ready to read from, but another connection was.

Examples

# Different commands to run for windows and unix
cmd1 <- switch(
  .Platform$OS.type,
  "unix" = c("sh", "-c", "sleep 1; ls"),
  c("cmd", "/c", "ping -n 2 127.0.0.1 && dir /b")
)
cmd2 <- switch(
  .Platform$OS.type,
  "unix" = c("sh", "-c", "sleep 2; ls 1>&2"),
  c("cmd", "/c", "ping -n 2 127.0.0.1 && dir /b 1>&2")
)

## Run them. p1 writes to stdout, p2 to stderr, after some sleep
p1 <- process$new(cmd1[1], cmd1[-1], stdout = "|")
p2 <- process$new(cmd2[1], cmd2[-1], stderr = "|")

## Nothing to read initially
poll(list(p1 = p1, p2 = p2), 0)

## Wait until p1 finishes. Now p1 has some output
p1$wait()
poll(list(p1 = p1, p2 = p2), -1)

## Close p1's connection, p2 will have output on stderr, eventually
close(p1$get_output_connection())
poll(list(p1 = p1, p2 = p2), -1)

## Close p2's connection as well, no nothing to poll
close(p2$get_error_connection())
poll(list(p1 = p1, p2 = p2), 0)

processx

Execute and Control System Processes

v3.5.2

MIT + file LICENSE

Authors

Gábor Csárdi [aut, cre, cph] (<https://orcid.org/0000-0001-7098-9676>), Winston Chang [aut], RStudio [cph, fnd], Mango Solutions [cph, fnd]

Initial release