Check whether a process PID exists or not
A positive integer.
There is no single go-to function in R 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
TRUE. If no working
approach is found,
pid_exists() will always return
regardless of PID tested.
On Unix, including macOS, alternatives
tools::pskill(pid, signal = 0L)
system2("ps", args = pid) are used.
On Windows, various alternatives of
system2("tasklist", ...) are used.
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.
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
Microsoft, tasklist, 2018-08-30, https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/tasklist
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
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