interpreter - Why is java bytecode interpreted? -

-

as far understand java compiles java bytecode, can interpreted machine running java specific cpu. java uses jit interpret bytecode, , know it's gotten fast @ doing so, why doesn't/didn't language designers statically compile down machine instructions once detects particular machine it's running on? bytecode interpreted every single pass through code?

the original design in premise of "compile once run anywhere". every implementer of virtual machine can run bytecodes generated compiler.

in book masterminds programming, james gosling explained:

james: exactly. these days we’re beating c , c++ compilers pretty always. when go dynamic compiler, 2 advantages when compiler’s running right @ last moment. 1 know chipset you’re running on. many times when people compiling piece of c code, have compile run on kind of generic x86 architecture. none of binaries particularly tuned of them. download latest copy of mozilla,and it’ll run on pretty intel architecture cpu. there’s pretty 1 linux binary. it’s pretty generic, , it’s compiled gcc, not c compiler.

when hotspot runs, knows chipset you’re running on. knows how cache works. knows how memory hierarchy works. knows how pipeline interlocks work in cpu. knows instruction set extensions chip has got. optimizes precisely machine you’re on. other half of sees application it’s running. it’s able have statistics know things important. it’s able inline things c compiler never do. kind of stuff gets inlined in java world pretty amazing. tack onto way storage management works modern garbage collectors. modern garbage collector, storage allocation extremely fast.


Comments

Post a Comment

Popular posts from this blog

php - What is the difference between $_SERVER['PATH_INFO'] and $_SERVER['ORIG_PATH_INFO']? -

-
what’s difference between $_server['path_info'] , $_server['orig_path_info'] ? how use them? when run print_r($_server) , path_info , orig_path_info not present in array. why not? how can enable them? i have read php manual on them, still don’t understand them. the path_info variable present if invoke php script this: http://www.example.com/phpinfo.php/hello_there it's /hello_there part after .php script. if don't invoke url that, there won't $_server["path_info"] environment variable. the porig_ prefix uncommon. path_info standard cgi-environment variable, , should never prefixed. did read that? (there issues around php3/php4 if invoked php interpreter via cgi-bin/ - hardly has such setups today.) for reference: http://www.ietf.org/rfc/rfc3875
Read more

fortran - Function return type mismatch -

-
i'm attempting recode old c++ program in fortran make use of lapack (i'm aware c++ have lapack++, i'm having lot of trouble installing it, gave up). i didn't have problems compilation, when had variables declared real . when started coding section of program required lapack, found parameters passed dsyev need double precision . tried change double precision (including changing hard coded numbers double precision counterparts, i.e. 0.0 -> 0.0d0) when try compile, following error of functions , subroutines i've written: error: return type mismatch of function <function> @ (1) (real(4)/real(8)) i'm not sure coming from, in program has been changed double precision. for example, i've declared following: double precision :: alpha(3),d(3),zeta1,zeta2 double precision :: a1(3),a2(3),d1(3),d2(3) double precision :: pi pi = 3.14159265359d0 alpha = (/0.109818d0, 0.405771d0, 2.22766d0/) d = (/0.444635d0, 0.535328d0, 0.154329d0 /) 10 i=1,3 ...
Read more

queue - mq_receive: message too long -

-
i implementing communication between 2 processes using queue. problem when call function mq_receive, error: message long. i have done following: struct mq_attr attr; long size = attr.mq_msgsize; .... // initializing queue "/gateway" int rc = mq_receive(gateway, buffer, size, &prio); if print size value, size=1, while when print same size program (got same mechanism), not long integer ( -1217186280 )... how can solve error?....so while size = 1, believe it's right "message long" why 1? p.s. have tried put : int rc = mq_receive(gateway, buffer, sizeof(buffer), &prio); but no result. it seems need read docs more carefully. when call mq_receive should pass size of destination buffer. this size must greater mq_msgsize attribute of queue . in addition, seems have error in queue attributes initialisation makes proper mq_receive call impossible. here standard message queue session: fill mq_attr struct ( doc ): struct mq_a...
Read more