D. Ungar, R. Smith, C. Chambers, and U. Holzle. Object, message, and performance: how they coexist in Self. IEEE Computer, 25(10):53--64, October 1992.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....analysis, followed by a translation to nativecode.Theessential difference between these approaches is when, where, and howmuchtimeisspent in performing these steps. The most popular approach is on the fly compilation, also known as just in time (or JIT) compilation [Incc, Incd, Incb, Wil, USCH92, GR83,Fra94] Analysis and translation are done online, typically during run time as each method (subroutine) is first called. However, analysis and translation can also be done at load time (e.g. during the bytecode verification process) or lazily on a per bytecode basis [Jon] The ....

D. Ungar, R. Smith, C. Chambers, and U. Holzle. Object, message, and performance: how they coexist in Self. IEEE Computer, 25(10):53--64, October 1992.

....feature that supports abstraction is the dynamic dispatch of methods based on the run time type of an object. In dynamically typed languages like Smalltalk and SELF, all dispatches are considered dynamic, and eliminating these dynamic dispatches has been essential to obtaining high performance [9, 14, 24]. C is a more conservatively designed language. Programmers must explicitly request dynamic dispatch by declaring a method to be virtual. C programs therefore suffer less of an initial performance penalty, at the cost of reduced flexibility and increased programAppears in the Proceedings of ....

Ungar, D., Smith, R. B., Chambers, C., and Holzle, U. Object, message, and performance: how they coexist in Self. Computer 25, 10 (Oct. 1992), 53--64. 14

....in the same scope. This capability permits objects (or procedures) to share operations and data defined within other objects (or procedures) Given this functionality, instances of an object may have different behaviors based on how they choose to delegate operations [Chambers and Ungar 1989; Ungar et al. 1992]. To illustrate, consider the familiar problem of specifying geometric objects. A box object consists of the x and y coordinates of its left corner, a length , a width , a method to move boxes from one coordinate to another, a method to clone a new instance of a box, and a print method to print ....

.... structured as (f r) would be rewritten as (f (barrier (reflect r (use x) barrier (reflect r (use y) 3) Customization: If all call points of a procedure abstracted over a public environment are known, its implementation can be specialized for each call [Chambers and Ungar 1989; Ungar et al. 1992]. Consider the expression below. let ( f (lambda (R) reflect R (use x) f (barrier (let ( x E) make public (x) reify) f (barrier (reify) If f does not escape, and its body is relatively small, this fragment can be translated to read, let ( f1 ....

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Ungar, D., Smith, R. B., Chambers, C., and H olzle, U. 1992. Object, message, and performance: How they co-exist in Self. IEEE Comput. 25, 10 (Oct.), 53--65.

....also address reification of continuations and stores, their emphasis is markedly different from ours. This results in a fairly sharp departure of our work from theirs both in the semantics of the reflective operators developed, and in the application domains addressed. Smalltalk [9] and Self [23] are two late binding languages that permit programmers to examine the context in which message evaluation occurs. The notion of a context in these languages is very similar to the notion of a reified environment in Rascal. In effect, contexts are first class environments. However, neither ....

David Ungar, Randall B. Smith, Craig Chambers, and Urs H olzle. Object, Message, and Performance: How They Co-Exist in Self. IEEE Computer, 25(10):53-- 65, October 1992.

....objects are in general identified by their addresses 9 , it is difficult to comprehend data structures where interconnections are represented by hexadecimal numbers. A graphical representation with objects as boxes and references as arrows like in the programming language and environment Self [14] makes debugging easier. Instant Replay for pSather efficiently reduces trace data. Nevertheless, the trace length is monotonically increasing with the program s run time. To provide deterministic replay for long running programs, the trace length must be limited. Checkpointing is an obvious ....

D. Ungar, R. Smith, C. Chambers, and U. Holzle. Object, message, and performance: how they coexist in Self. Computer, 25(10):53--64, Oct. 1992.

....Other members of our group at DIT are also working on comparing these and a few public domain OO systems on Mips and Alpha architectures using native C compilers and Sather with a native C compiler 1 . 3 Customisation Tradeoffs Customisation is an optimisation technique first used in Self [4, 29]. Customised code runs exclusively on instances of one particular subclass. In customised code the type of self is known at compile time. All attribute offsets and self calls can therefore be resolved at compile time, self calls to small functions can be inlined. As mentioned above, fully ....

D. Ungar, R.B. Smith, C. Chambers, and U. Holzle: Object, Message, and Performance: How They Coexist in Self. IEEE Computer, 10, 1992.

....they are young. This illustrates the type of errors that occur frequently, yet we believe can only be realistically detected by humans. 10 We intend to enhance the coverage. 16 . The ability to treat CODE4 concepts as programmable objects, combining ideas from delegation systems such as Self (Ungar 1992) and constraint management systems such as Garnet (Myers, Giuse et al. 1990) We have had the most experience with the first functionality listed above, which we call delegation . An example of a block in the syntax we use is found in the condition property for batteries, below. These blocks, ....

Ungar, D., Smith, R., Chambers, C., Holzle, U. (1992). Object, Message, and Performance: How They Coexist in Self. Computer, Oct: 53-64.

....any method, even inlined ones, with no interference from the implementation. 4.1 Transparent Efficiency The implementation techniques for Self have been presented previously so we will only summarize the briefly here. See [Hol94] HU94a] HCU92] HCU91] Cha92] CU91] CU90] CUL89] and [USCH92] for more details. Self presented large efficiency challenge because its pure semantics implied that every access, assignment, arithmetic operation and control structure had to be performed by sending a message. Worse yet, the Self user interface s uncompromising stance on structural reification ....

David Ungar, Randall B. Smith, Craig Chambers, and Urs Hölzle. Object, Message, and Performance: How They Coexist in Self. Computer, 25(10), pp. 53-64. (October 1992).

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