Revision: 1067
http://svn.sourceforge.net/r-gregmisc/?rev=1067&view=rev
Author: warnes
Date: 2007-03-06 15:15:31 -0800 (Tue, 06 Mar 2007)
Log Message:
-----------
Create manual pages for handleSIGCLD() and restoreSIGCLD(), as well as appropriately modifying the pages for fork() and signal()
Modified Paths:
--------------
trunk/fork/man/fork.Rd
trunk/fork/man/signal.Rd
Added Paths:
-----------
trunk/fork/man/handleSIGCLD.Rd
Modified: trunk/fork/man/fork.Rd
===================================================================
--- trunk/fork/man/fork.Rd 2007-03-06 22:47:29 UTC (rev 1066)
+++ trunk/fork/man/fork.Rd 2007-03-06 23:15:31 UTC (rev 1067)
@@ -162,12 +162,11 @@
close(con2)
}
-\dontrun{
-# Important: if we aren't going to explicitly wait() for the child
-# process to exit, we need to tell the OS that we are ignoring child
-# process signals so it will let us die cleanly.
-signal("SIGCHLD","ignore")
-}
+## Important: if we aren't going to explicitly wait() for the child
+## process to exit, we need to set up a dummy signal handler to collect
+## (and then throw away) the exit status so that child processes will not
+## become zombies when they exit
+handleSIGCLD()
# fork off the process
pid <- fork(recieve)
@@ -175,6 +174,9 @@
# start sending...
send()
}
+
+## restore SIGCLD signal handling to the previous state
+restoreSIGCLD()
}
\keyword{programming}
Added: trunk/fork/man/handleSIGCLD.Rd
===================================================================
--- trunk/fork/man/handleSIGCLD.Rd (rev 0)
+++ trunk/fork/man/handleSIGCLD.Rd 2007-03-06 23:15:31 UTC (rev 1067)
@@ -0,0 +1,57 @@
+\name{handleSIGCLD}
+\alias{handleSIGCLD}
+\alias{restoreSIGCLD}
+\title{Establish or remove a dummy handler for SIGCLD signals}
+\description{
+ Establish \code{handleSIGCLD} or remove \code{ignoreSIGCLD} a dummy
+ handler for SIGCLD signals
+}
+\usage{
+handleSIGCLD()
+restoreSIGCLD()
+}
+\details{
+ The \code{handleSIGCLD} function establishes a 'dummy' handler for
+ SIGCLD signals. It accepts signals from exiting child processes
+ created by \code{fork} and ignores them. This prevents child
+ processes from becoming 'zombies', which would occurs when the parent
+ process does not handle this signal.
+
+ The \code{restoreSIGCLD} function restores the previous (lack of)
+ signal handler.
+}
+\value{
+ No return value.
+}
+\note{
+ The SIGCLD handling mechanism implemented by \code{handleSIGCLD}
+ should prevent zombie process creation on systems derived from both
+ SYSV and BSD UNIX, including Linux, Mac OSX, NetBSD, and Solaris.
+ }
+\references{W.R. Stevens and S.A. Rago, Advanced Programming in the UNIX
+ environment, 2nd ed. (c) 2005, Pearson Education, pp 308-310.}
+\author{Gregory R. Warnes \email{gre...@ro...} }
+\seealso{ \code{\link{fork}}, \code{\link{wait}}, \code{\link{signal}} }
+\examples{
+
+## set up the dummy signal hander
+handleSIGCLD()
+
+## Generate 100 child processes
+for(i in 1:100)
+ {
+ pid = fork(slave=NULL)
+ if(pid==0)
+ {
+ ## don't do anything useful
+ exit()
+ }
+ else
+ pidList[i] <- pid
+ }
+
+## remove the dummy signal handler
+restoreSIGCLD()
+}
+\keyword{programming}
+
Modified: trunk/fork/man/signal.Rd
===================================================================
--- trunk/fork/man/signal.Rd 2007-03-06 22:47:29 UTC (rev 1066)
+++ trunk/fork/man/signal.Rd 2007-03-06 23:15:31 UTC (rev 1067)
@@ -26,11 +26,23 @@
\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 \code{handleSIGCLD} function for a mechanism that
+ will prevent child processes from becoming zombies on both SYSV and
+ (hopefully) BSD-derived systems.
}
-\seealso{ \code{\link{sigval}}, \code{\link{fork}} }
+\seealso{ \code{\link{sigval}}, \code{\link{fork}}, \code{\link{handleSIGCLD}} }
\examples{
\dontrun{
-# Ignore child termination signals for forked processes
+## 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!".
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