mkopk.blogg.se - Needs flash player 8 and javascript enabled

Tamarin, the VM in Flash, uses the JIT approach, while the WebKit JavaScript VM is a bytecode interpreter.

It doesn't have as much profiling information, but it also can spend longer optimising because the end user isn't waiting for the compiler to run, so it tends to be faster than JIT compilation in practice. Great for long-running programs, not so good for other things. This can produce the fastest code, because it can be tailored for that specific run of the program, but the cost of generating the code has to be added to the cost of running it every time that you run the program. Functions (or traces in something like Tamarin) are compiled to native code as they are needed, or after running them in an interpreter a few time and getting profiling information. Just-in-time compiling to native code.Significantly faster than interpreting an AST. A simple assignment would be a push value, push address and pop value at address bytecode instruction, which would expand to half a dozen or so native instructions. You can implement them with a jump table, so the interpreter is fast (typically 50% native speed or more). Bytecodes are instruction sets for virtual stack machines where each opcode is one byte. Compiling the AST to bytecode and interpreting the bytecode.It's very slow, because something like 'a = b' involves three AST nodes and so you need at least three function calls for a trivial assignment. This is how JavaScript was implemented in browsers until a couple of years ago. Whenever you run a bit of code, you do a traversal of the tree and execute each node in turn.

Interpreting the AST (or even parse tree).

There are, roughly speaking, four ways of implementing a programming language, although the boundaries between them are sometimes blurred. This gives the Flash VM a little while to spend compiling and executing the code. The test suite that the WebKit team use runs in a couple of seconds on a decent computer, while a typical Flash game will often take at least 10 seconds to download all of the image and sound files that it needs. The main requirement for Flash is efficiency of generated code, while for JavaScript it's load time. JavaScript in a browser tends to do relatively simple things and uses a tiny bit of CPU. Flash tends to run very long-running things, like games which use a big chunk of CPU for several minutes at a time. It's worth noting that Adobe and the browser makers optimise their VMs for different requirements.