1 files changed, 42 insertions, 0 deletions
diff --git a/code/snippets/signals_chld_nohang.rb b/code/snippets/signals_chld_nohang.rb
new file mode 100644
index 0000000..621a70c
--- /dev/null
+++ b/code/snippets/signals_chld_nohang.rb
@@ -0,0 +1,42 @@
+child_processes = 3
+dead_processes = 0
+# We fork 3 child processes.
+child_processes.times do
+  fork do
+    # They sleep for 3 seconds.
+    sleep 3
+  end
+end
+
+# Sync $stdout so the call to #puts in the CHLD handler isn't
+# buffered. Can cause a ThreadError if a signal handler is
+# interrupted after calling #puts. Always a good idea to do
+# this if your handlers will be doing IO.
+$stdout.sync = true
+
+# Our parent process will be busy doing some intense mathematics.
+# But still wants to know when one of its children exits.
+
+# By trapping the :CHLD signal our process will be notified by the kernel
+# when one of its children exits.
+trap(:CHLD) do
+  # Since Process.wait queues up any data that it has for us we can ask for it
+  # here, since we know that one of our child processes has exited.
+
+  # We loop over a non-blocking Process.wait to ensure that any dead child
+  # processes are accounted for.
+  begin
+    while pid = Process.wait(-1, Process::WNOHANG)
+      puts pid
+      dead_processes += 1      
+    end
+  rescue Errno::ECHILD
+  end
+end
+
+loop do
+  # We exit ourself once all the child processes are accounted for.
+  exit if dead_processes == child_processes
+  
+  sleep 1
+end