pid_exists function

Check whether a process PID exists or not

pid_exists(pid, debug = getOption("parallelly.debug", FALSE))

Arguments

• pid: A positive integer.

Returns

Returns TRUE if a process with the given PID exists, FALSE if a process with the given PID does not exists, and NA if it is not possible to check PIDs on the current system.

Details

There is no single go-to function in for testing whether a PID exists or not. Instead, this function tries to identify a working one among multiple possible alternatives. A method is considered working if the PID of the current process is successfully identified as being existing such that pid_exists(Sys.getpid()) is TRUE. If no working approach is found, pid_exists() will always return NA

regardless of PID tested. On Unix, including macOS, alternatives tools::pskill(pid, signal = 0L)

and system2("ps", args = pid) are used. On MS Windows, various alternatives of system2("tasklist", ...) are used. Note, some MS Windows machines are configures to not allow using tasklist on other process IDs than the current one.

References

1. The Open Group Base Specifications Issue 7, 2018 edition, IEEE Std 1003.1-2017 (Revision of IEEE Std 1003.1-2008) https://pubs.opengroup.org/onlinepubs/9699919799/functions/kill.html
2. Microsoft, tasklist, 2021-03-03, https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/tasklist
3. R-devel thread 'Detecting whether a process exists or not by its PID?', 2018-08-30. https://stat.ethz.ch/pipermail/r-devel/2018-August/076702.html

See Also

pskill() and system2().