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Re: Distributed Objects help - a fun hack

On Tuesday, September 4, 2001, at 01:33 PM, Miguel Morales wrote:

Dear Peter,

DO works VERY hard to keep everything thread safe (even object double pointers get dereferenced). This is the reason for the NSDistantObjects you are getting. Now there are situations where you can guarantee that an object will not be accessed by multiple threads, and you don't want the overhead of using the 'bycopy' keyword. The hack I have found to this is the following set of calls, making use of casting so that the DO system does not know an object is involved. I have no idea if this will survive various upgrades, but it works on both OS X 10.0.4 and GNUStep under Linux without any problems (just a compiler warning). If anyone out there knows of a better method, I'd love to hear it.

Hi Miguel, and thanks for your great response. You're right, DO does work very hard: it ferreted out my object pointers even when I wrapped them in a struct!

Casting the pointer to a long is a clever trick, and one that I hadn't thought of.

A solution that worked for me was to record the object pointer in instance variables (declared volatile!) of the object I'd send the message to; the method performed in the main thread could just grab the "parameters" from its instance variables. I imagine that the synchronization required to prevent overwriting still-needed parameters made that inefficient.

If I may offer a suggestion: currently, sending a void* parameter between threads results in a runtime error because the runtime doesn't know how to encode what the void* points to. Instead of that, why not make the runtime pass the void* pointer like it passes primitives? That would obviate the need for implementation-defined hacks like passing pointers in ints.

Thanks once more!

[snip]

-Peter

References: 
 >Re: Distributed Objects help - a fun hack (From: Miguel Morales <email@hidden>)



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