From: Robert Klemme <shortcutter@...>
Date: 2007-06-08T05:35:04+09:00
Subject: Re: raise problem in Thread

On 07.06.2007 22:03, Oliver Peng wrote:
> So when we call raise method, we are calling the MyThread instance's 
> raise method and it stop running of MyThread instance. I tried to use 
> Kernel.raise and Thread.current.raise. They all work fine and raise 
> exception in main thread.

Basically whenever you invoke "raise" somewhere in code it's really 
Kernel's raise which delegates to Thread.current.raise.  As you see, 
#raise is also an instance method of Thread so your situation was 
special because your class inherited Thread.  That's why the raise had a 
slightly different effect, namely raising the exception in that thread 
and not in the calling thread.  Maybe this helps clarify:

irb(main):001:0> Thread.current.methods.grep /raise/
=> ["raise"]
irb(main):002:0> Thread.instance_methods.grep /raise/
=> ["raise"]
irb(main):003:0> method :raise
=> #<Method: Object(Kernel)#raise>
irb(main):004:0> Thread.current.method :raise
=> #<Method: Thread#raise>

It's often confusing when first confronted with multithreading in OO 
languages like Ruby and Java: Thread's are instances (i.e. objects) like 
all other objects but at the same time, there is a thread of execution 
(i.e. stack, program counter etc.) associated with them.  But this 
relationship is not fixed: you can have Thread objects with no execution 
thread associated.  In Java this is between creation of a Thread 
instance and invoking start() and after the thread terminated.  In Ruby, 
since threads are started immediately, it's only after a thread terminated.

Kind regards

	robert