mention the C<$SIG{CHLD} = 'IGNORE'> special case

p4raw-id: //depot/perl@2152

diff --git a/pod/perlfunc.pod b/pod/perlfunc.pod
index 58c3e71..e72624f 100644 (file)
--- a/pod/perlfunc.pod
+++ b/pod/perlfunc.pod
@@ -4432,7 +4432,8 @@ If you know the exact length in bits, it can be used in place of the C<*>.
 
 Waits for a child process to terminate and returns the pid of the
 deceased process, or C<-1> if there are no child processes.  The status is
-returned in C<$?>.
+returned in C<$?>.  Note that a return value of C<-1> could mean that
+child processes are being automatically reaped, as described in L<perlipc>.
 
 =item waitpid PID,FLAGS
 
@@ -4451,7 +4452,8 @@ FLAGS of C<0> is implemented everywhere.  (Perl emulates the system call
 by remembering the status values of processes that have exited but have
 not been harvested by the Perl script yet.)
 
-See L<perlipc> for other examples.
+Note that a return value of C<-1> could mean that child processes are being
+automatically reaped.  See L<perlipc> for details, and for other examples.
 
 =item wantarray
 

diff --git a/pod/perlipc.pod b/pod/perlipc.pod
index cc2a1a9..c74c520 100644 (file)
--- a/pod/perlipc.pod
+++ b/pod/perlipc.pod
@@ -56,7 +56,17 @@ So to check whether signal 17 and SIGALRM were the same, do just this:
 
 You may also choose to assign the strings C<'IGNORE'> or C<'DEFAULT'> as
 the handler, in which case Perl will try to discard the signal or do the
-default thing.  Some signals can be neither trapped nor ignored, such as
+default thing.
+
+On most UNIX platforms, the C<CHLD> (sometimes also known as C<CLD>) signal
+has special behavior with respect to a value of C<'IGNORE'>.
+Setting C<$SIG{CHLD}> to C<'IGNORE'> on such a platform has the effect of
+not creating zombie processes when the parent process fails to C<wait()>
+on its child processes (i.e. child processes are automatically reaped).
+Calling C<wait()> with C<$SIG{CHLD}> set to C<'IGNORE'> usually returns
+C<-1> on such platforms.
+
+Some signals can be neither trapped nor ignored, such as
 the KILL and STOP (but not the TSTP) signals.  One strategy for
 temporarily ignoring signals is to use a local() statement, which will be
 automatically restored once your block is exited.  (Remember that local()

diff --git a/pod/perlvar.pod b/pod/perlvar.pod
index 739dd55..af5f62f 100644 (file)
--- a/pod/perlvar.pod
+++ b/pod/perlvar.pod
@@ -835,6 +835,10 @@ signals.  Example:
     $SIG{'INT'} = 'DEFAULT';   # restore default action
     $SIG{'QUIT'} = 'IGNORE';   # ignore SIGQUIT
 
+Using a value of C<'IGNORE'> usually has the effect of ignoring the
+signal, except for the C<CHLD> signal.  See L<perlipc> for more about
+this special case.
+
 The %SIG array contains values for only the signals actually set within
 the Perl script.  Here are some other examples: