From: Robert Klemme <shortcutter@...>
Date: 2008-03-06T02:44:55+09:00
Subject: Re: SystemStackError: stack level too deep

On 03.03.2008 21:54, Oliver Peng wrote:
> Robert Klemme wrote:
>> 2008/3/3, Oliver Peng <oliver.peng@skywave.com>:
>>> Robert Klemme wrote:
>>>  as the sample code in book 'Programming ruby'.
>> There is no trace of Process.waitall in the signal handler sample code.
>>
>>>  When a child process dies, a signal, SIGCHLD (or SIGCLD) is sent to its
>>>  parent process. So when I run Process.wait, I always should get the
>>>  response at once. And this code can work. The only problem is sometimes
>>>  SystemStackError was raised.
>>>
>>>  Can you please use sample code to show me where is the problem?
>> The problem is in waitall.  The sample code otherwise works ok.  Try 
>> this
>>
>> trap "CLD" do
>>   puts "#{Process.wait} exited"
>>   # alternative
>>   p Process.wait2
>> end
>>
>> 5.times do |i|
>>   pid = fork do
>>     puts "proc #{i}"
>>   end and puts "#{pid} created"
>> end
>>
>> puts "all children created"
>>
>> sleep 10
>>
>> Here's another approach
>>
>> require 'pp'
>>
>> 5.times do |i|
>>   pid = fork do
>>     puts "proc #{i}"
>>   end and puts "#{pid} created"
>> end
>>
>> puts "all children created"
>>
>> pp Process.waitall
>>
>>
>> Kind regards
>>
>> robert
> 
> Ok. I see. You mean that waitall shouldn't be used in trap 'CLD' because 
> it would wait until all process exit.
> 
> But I use wait at first and get the SystemStackError exception. Then I 
> try to use waitall later. So I still don't know why the SystemStackError 
> exception is raised.
> 
> I also try to write test code and please have a look:
> 
> ----------------------------------------------------
> Server code:
> require 'socket'
> 
> trap('CLD') do
>   pid = Process.wait
>   puts "pid #{pid} exited"
> end
> 
> class TestServer
> 
> def initialize
>   @tcpServer = TCPServer.new('0.0.0.0', 7777)
> end
> 
> def run
>   while tcp = @tcpServer.accept
>     fork do
>       begin
>   while str = tcp.gets()
>     tcp.puts("hello")
>   end
>       ensure
>   tcp.close_read
>   tcp.close_write
>       end
>     end
>     tcp.close
>   end
> end
> end
> 
> server = TestServer.new
> 
> server.run
> 
> ------------------------------------------------
> Client code:
> 
> require 'socket'
> 
> threads = []
> 100.times do
>   threads << Thread.new() do
>     while true
>       socket = TCPSocket.new('localhost', 7777)
>       socket.puts("hello")
>       sleep 1
>       socket.gets
>       socket.close
>       sleep 10
>     end
>   end
> end
> 
> threads.each {|thr| thr.join}
> 
> From the server output, I can see that CLD signal has been traped and 
> server puts the process exit. But from top I can see that zombie process 
> are getting more and more. Is there some problem in the code logic?

I can't really see one.  Can you post the exception with the stack trace?

Kind regards

	robert