Her (at the time, his) kernel had several interesting features. One was run-time code generation. Another was an object system much less indirect than the standard C++ vtable approach; you know,
mov (%eax), %eax
mov 16(%eax), %eax
call *%eax
That involves two memory fetches.
One step less indirect would be to copy the vtable into every object, which of course means that every object could have a separate vtable. Synthesis's quajects are two steps more indirect: every object has a separate copy of every method. So a method call looked like (the 68030 equivalent of)
add $32, %eax
call *%eax
No memory fetches.
The fact that every object had its own copy of each method meant that the method could be optimized for that object. If it was more than a few instructions long, you'd want to factor the main body of the method into a regular function, but many methods are not.
One of the interesting features of Quajects is that you can instantiate a quaject not only with its own data but with its own "callouts". In a traditional object system, wherever you have a simple little object, that object implicitly carries within it this whole pyramid of things that it calls, and things that those things call, and so on — allocators, file buffers, system calls, and so on. More flexible languages like Ruby have facilities for temporarily replacing some part of that pyramid, say, for testing. But each call out of a quaject is just as overridable as an instance variable. When you instantiate the quaject, you supply callouts to it.
There are several more interesting features in Synthesis, including lock-free synchronization (not a new invention at the time, but popularized by Synthesis) and PLL scheduling for soft-real-time response. Also, the dissertation is a rollicking good read.
One step less indirect would be to copy the vtable into every object, which of course means that every object could have a separate vtable. Synthesis's quajects are two steps more indirect: every object has a separate copy of every method. So a method call looked like (the 68030 equivalent of)
No memory fetches.The fact that every object had its own copy of each method meant that the method could be optimized for that object. If it was more than a few instructions long, you'd want to factor the main body of the method into a regular function, but many methods are not.
One of the interesting features of Quajects is that you can instantiate a quaject not only with its own data but with its own "callouts". In a traditional object system, wherever you have a simple little object, that object implicitly carries within it this whole pyramid of things that it calls, and things that those things call, and so on — allocators, file buffers, system calls, and so on. More flexible languages like Ruby have facilities for temporarily replacing some part of that pyramid, say, for testing. But each call out of a quaject is just as overridable as an instance variable. When you instantiate the quaject, you supply callouts to it.
There are several more interesting features in Synthesis, including lock-free synchronization (not a new invention at the time, but popularized by Synthesis) and PLL scheduling for soft-real-time response. Also, the dissertation is a rollicking good read.
http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.29.4...