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comp.lang.ruby

handle exception thrown in nested threads from top level thread

hemant

9/18/2006 10:16:00 AM

In following code, both methos get_client_symbol and sync_clients gets
called and they start their own new threads. Now, what I would like to
do is, whenever a exception is raised from the nested threads..i would
like to catch them in the toplevel thread.

Now..I have tried many things:
Thread.abort_on_exception = true
and using just rescue or rescue Exception or rescue RuntimeError,
however the exception raised in nested threads won't get caught in the
top level thread. Any clues?

@threads << Thread.new do
child_threads = []

begin
child_threads << get_client_symbol(temp_client_id)
child_threads << sync_clients(temp_client_id)
child_threads.each {|thr| p thr.to_s; thr.join; }

rescue Exception
p $!
p $!.backtrace
# delete the values from list
@connected_clients.synchronize do
@connected_clients.delete(temp_client_id)
@symbols_being_added.signal
end #end of sync
child_threads.each {|thr| Thread.kill(thr) if thr.alive? }
end

end #end of threads


--
There was only one Road; that it was like a great river: its springs
were at every doorstep, and every path was its tributary.
1 Answer

Robert Klemme

9/18/2006 10:40:00 AM

0

On 18.09.2006 12:15, hemant wrote:
> In following code, both methos get_client_symbol and sync_clients gets
> called and they start their own new threads. Now, what I would like to
> do is, whenever a exception is raised from the nested threads..i would
> like to catch them in the toplevel thread.
>
> Now..I have tried many things:
> Thread.abort_on_exception = true
> and using just rescue or rescue Exception or rescue RuntimeError,
> however the exception raised in nested threads won't get caught in the
> top level thread. Any clues?

There is no direct way. If you think about it for a moment it's not
possible to catch an exception thrown in another thread. But in Ruby
you can actually do that by rethrowing it in another thread. Try this:


print "Main thread : ", Thread.current.inspect, "\n"

2.times do
Thread.new(Thread.current) do |parent|
print "Child thread: ", Thread.current.inspect, "\n"

loop do
begin
puts "."
raise "Foo" if rand > 0.8
sleep 1
rescue Exception => e
print "Thread : ",
Thread.current.inspect,
": ",
e.inspect,
"\n"
parent.raise e
end
end
end
end


10.times do
begin
sleep 10
rescue Exception => e
print "Thread main: ",
Thread.current.inspect,
": ",
e.inspect,
"\n"
puts e.backtrace
end
end


Kind regards

robert