Your problem is that the UI process (which is responsible for invoking #step) waits for the promise to compute its value. However, that promise will only be evaluated upon the next step, which would have to be run via the UI process which blocks on the promise. In short, you have a classic deadlock.
Yes I see that :). Naively I was thinking that Morphic was more concurrent. I was wondering how I can introduce more concurrency in the problem. I'm bit afraid by the idea of forking the stepping mechanism. I will try to see how I can make a workspace that does not create the deadlock and play with the solutions suggested by boris.
I was wondering if other people using Morphic for simulation did not get the same problem
Stef
On 31 janv. 04, at 23:03, Andreas Raab wrote:
Hi Stef,
Cheers,
- Andreas
----- Original Message ----- From: "ducasse" ducasse@iam.unibe.ch To: "The general-purpose Squeak developers list" squeak-dev@lists.squeakfoundation.org Sent: Sunday, February 01, 2004 1:52 AM Subject: Multi-thread Question in Morph?
Hi all
I'm designing a simple environment with a bot evolving in a maze. The user can control the bots from a kind of workspace. In an old implementation, I did not use step and put some delay and World doOneCycle. Not so good. I decided to clean that and to use the step method to execute commands sent to this morph.
The morph has a queue of actions (which are reified message sends with a future to hold their result).
For example the method go is implemented as NewBot>>go
self addAction: #goPrimitive
this means that when the action is executed the method goPrimitive will be executed which is in fact implemented.
goPrimitive
self position: (self position + (10@10))
addAction: and similar methods are implemented that way: a command object is created and put in the queue and returned.
addAction: aSelector arguments: anArray
| anAction | anAction := (BotCommand selector: aSelector arguments: anArray). actionQueue addLast: anAction. ^ anAction
A command object is a message reification that holds a future so that I can get result back to the sender when necessary (for exmaple getter method, as in the following example. result in that case get the future and ask its value.
diamNumber
^ (self addAction: #diamNumberPrimitive) result
The step method goes over the queue and execute the actions one after the other. It then puts the future value
step
| action res | ^ actionQueue isEmpty ifFalse: [action := self removeAction. res := self perform: action selector withArguments: action arguments. action setFutureValue: res]
Now I have the following problem that you can try just by loading the cs. If I create a morph NewBot new openInWorld, inspect it and execute self diamNumber in an inspector, the complete environment is blocked.
I simplified the problem to its essence in the attached file. If you open an inspect and evaluate self diamNumber the system freezes. Apparently there is not enough thread in morphic. So I started to see where I could put another thread. The problem is that
- in an inspector doing [self diamNumber] fork does not help because I
would need another future to get the value form the thread
- opening an inspector in another block (self inspect fork) and in
this new inspector doing self diamNumber still freezes the system My impression is that the UI scheduler does not let me doing that.
does anybody has an idea of how I could solve that problem?
stef