2009/8/7 Dale Henrichs <dale.henrichs@gemstone.com>:

I'm trying to characterize some differences in behavior for GemTools between Squeak and the 1.0beta for Pharo. I'm not reporting a bug as much as trying to understand what I need to do differently in Pharo.

In GemTools, I have a special workspace (GemTools Launcher), that causes doits to be evaluated in a GemStone server. This is done by using FFI to make calls to the GemStone GCI library.

The string is passed to GemStone via a nonblocking C call. On the Pharo (client) side, we poll for a result. While an expression is evaluating, exceptions may be raised on the server-side and on the client, we convert the gemstone exception into a Pharo exception and signal it, if/when the exception is resumed, we pass a result back to the server and continue waiting for the result of the original expression.

There are two thing that might happen when a exception is raised in this manner. If the exception is an error, we bring up a debugger window on the client and arrange to debug the process on the server (again using the GCI). If the exception is what we call a Client Forwarder exception, then we arrange to send a message to the client object and pass the result back to the server side. Using a client forwarder, the server can send messages to the client Transcript with logging/progress messages.

In earlier versions of Pharo and in the current version of Squeak, when we sent messages to the Transcript, the messages would show up immediately ... making it easy to watch progress of long running operations.

In the 1.0 beta Pharo, this behavior has changed. It appears that the Transcript window is not updated until the polling process finishes, which makes the progress messages a little bit less than useful.

I assume that I need to add a message to my polling loop to allow for display updates...I'm doing a Delay wait in the loop so the process is not in a tight loop.

I am not running the poll in the background, because I want the UI process to be blocked ... this same mechanism is used for menu items, etc. so blocking is important.

Thanks for the help,

Dale, the key problem of this is that 'wait loop' blocks the UI process. I know, it is simplest way to prevent user from doing anything while system is busy but its not very friendly, especially when you need to perform a remote processing which requires a substantional amount of time to complete. But, i wonder, what is the point in using a non-blocking calls to communicate with GemStone, when in the end its still blocks everything (from user's point of view) ? :) Stef did a good job making a Transcript thread-safe in Pharo, so it can be used by any process (not only UI one) safely. But this implies that you should not block the UI thread to give it a chance to update the screen. In case if nothing blocks the process, the transcript window will be updated each 20ms or so (World update cycle), and such delay, i think will be hardly noticeable by users. Transcript is a stream , which updated immediately once you putting something to it, but there are no guarantees that any other objects (like window , which is displaying its contents) should be updated immediately as well. I am encouraging you to create a background process , which talks with GemStone, and then UI process just schedule user actions to it. This will make UI process non-blocking, but of course, requires additional efforts, like disabling the user from doing anything while waiting response from G/S. But this could be done nicely, and user could go to any other window/menu etc, and do things there while G/S processing the actions. Which i think makes UI much more friendly.

Dale

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