signal: Enable or disable handling of signals

In warnes/fork: R Functions for Handling Multiple Processes

Description

This function allows enabling or disabling handling of the specified signal.

Usage

signal(signal, action = c("ignore", "default"))

Arguments

signal	Signal handler to manipulate, either as a numeric id or character mnemonic
action	Either "ignore" or "default"

Details

It is occasionally necessary to instruct the R process to ignore certain signals. This function allows changing the status of a signal to either igore the signal (SIG\_IGN="ignore") or to the OS's default handler (SIG\_DFL="default")

Value

Nothing of interest.

Note

Be very careful with this function. It can be used to totally confuse the R process.

On sytems derived from BSD UNIX, setting the SIGCHLD signal to 'ignore' will allow child processes to exit cleanly without becoming zombies. This also prevents the parent process from checking the exit status of children, since this information is no longer available once child process disappears. On systems derived from SysV UNIX, setting SIGCHLD to 'ignore' has no effect on the status of child processes that exit, and they will still become zombies unless the exit status is checked. See the handleSIGCLD function for a mechanism that will prevent child processes from becoming zombies on both SYSV and (hopefully) BSD-derived systems.

Author(s)

Gregory R. Warnes [e-mail], with financial support from Metrum Research Group, LLC http://www.metrumrg.com.

References

See the unix man page for "signal" for more information

See Also

sigval, fork, handleSIGCLD

Examples

## Not run: 
## Ignore child termination signals for forked processes NOTE: This
## mechanism only works on UNIX SYSV-derived systems. See Note above.
signal("SIGCHLD","ignore")

# Fork off a child process to say "Hi!".
 {
    pid = fork(slave=NULL) 
    if(pid==0) {
      # only runs in the child process
      cat("Hi from the child process!\n");
      exit() # force process to die
    } 
 } 

## End(Not run)

warnes/fork documentation built on May 4, 2019, 12:59 a.m.