JAVA的动态编译和静态编译
2008-01-05 09:08:10 来源:WEB开发网 闂傚倸鍊搁崐鎼佸磹閹间礁纾归柟闂寸绾惧綊鏌熼梻瀵割槮缁炬儳缍婇弻鐔兼⒒鐎靛壊妲紒鐐劤缂嶅﹪寮婚悢鍏尖拻閻庨潧澹婂Σ顔剧磼閹冣挃闁硅櫕鎹囬垾鏃堝礃椤忎礁浜鹃柨婵嗙凹缁ㄧ粯銇勯幒瀣仾闁靛洤瀚伴獮鍥敍濮f寧鎹囬弻鐔哥瑹閸喖顬堝銈庡亝缁挸鐣烽崡鐐嶆棃鍩€椤掑嫮宓佸┑鐘插绾句粙鏌涚仦鎹愬闁逞屽墰閹虫捇锝炲┑瀣╅柍杞拌兌閻ゅ懐绱撴担鍓插剱妞ゆ垶鐟╁畷銉р偓锝庡枟閻撴洘銇勯幇闈涗簼缂佽埖姘ㄧ槐鎾诲礃閳哄倻顦板┑顔硷工椤嘲鐣烽幒鎴旀瀻闁规惌鍘借ⅵ濠电姷鏁告慨顓㈠磻閹剧粯鈷戞い鎺嗗亾缂佸鏁婚獮鍡涙倷閸濆嫮顔愬┑鐑囩秵閸撴瑦淇婇懖鈺冪<闁归偊鍙庡▓婊堟煛鐏炵硶鍋撻幇浣告倯闁硅偐琛ラ埀顒冨皺閺佹牕鈹戦悙鏉戠仸闁圭ǹ鎽滅划鏃堟偨缁嬭锕傛煕閺囥劌鐏犻柛鎰ㄥ亾婵$偑鍊栭崝锕€顭块埀顒佺箾瀹€濠侀偗婵﹨娅g槐鎺懳熺拠鑼舵暱闂備胶枪濞寸兘寮拠宸殨濠电姵纰嶉弲鎻掝熆鐠虹尨宸ョ€规挸妫濆铏圭磼濡搫顫嶇紓浣风劍閹稿啿鐣烽幋锕€绠婚悹鍥у级瀹撳秴顪冮妶鍡樺鞍缂佸鍨剁粋宥夋倷椤掍礁寮垮┑鈽嗗灣閸樠勭妤e啯鍊垫慨妯煎亾鐎氾拷

核心提示:Two popular apPRoaches for compiling java programs are Just-In-Time (JIT) compilation (e.g. Sun Hotspot [29], Cacao [18], OpenJIT [24], shuJIT [28], vanilla Jal
Two popular apPRoaches for compiling java programs are Just-In-Time (JIT) compilation (e.g. Sun Hotspot [29], Cacao [18], OpenJIT [24], shuJIT [28], vanilla Jalapeno [1]) and static compilation (e.g. BulletTrain [22], Excelsior JET [10], GCJ [32], IBM VisualAge for Java [14], JOVE [15]). It would be wrong to say one approach is definitely better than the other, since they are suited for different situations [7]. In fact, current research on ``quasi-static compilation'' [27] shows that combining these two may yield Excellent results.
In practice, static Java compilers are sometimes desirable over JIT compilers because they have many advantages [3,5,7]:
Static compilation yields more robust deployed applications. On the one hand, a deployment JIT may be different from the development JIT, which can cause problems due to even slight differences in the virtual machine or library code. With static compilation, programs are compiled into native code allowing the developer to test exactly what is deployed. On the other hand, compilers have bugs. Crashes caused by static compiler bugs sometimes happen at compile time (unless the bug is the kind that generates bad code silently), while bugs in the JIT may cause crashes at program execution time, and some of them may only surface after a portion of the program has been executed many times. Moreover, if the program crashes due to a bug in either the compiler or the program itself, statically compiled code is mUCh easier to debug because the run-time trace is more predictable.
Static compilation provides better intellectual property protection. Native code is much harder to reverse-engineer than Java bytecode.
Static Java compilers can perform resource intensive optimization before the execution of the program. In contrast, JIT compilers must perform analysis at execution time, thus are limited to simple optimizations that can be done without a large impact on the combined compile and execute time.
Static compilation achieves greatly reduced start-up cost, reduced memory usage, automatic sharing of code by the OS between applications, and easier linking with native code.
Last but not least, static compilation is better suited for code certification than JIT compilation. It is significantly easier to achieve higher safety assurance by removing the compiler from the trusted computing base. There has been a lot of work done in this area [23,21,19] which mostly focuses on static compilation.
Regardless of the above advantages, there is an ongoing debate in the Java community on whether statically compiled implementations can meet the Java specification on dynamic features such as binary compatibility. Our paper presents a scheme that accommodates the seemingly contradictory goal of full Java compliance and static compilation, thus showing that binary compatibility can indeed be supported using static compilers. Following the inspiration of ``quasi-static compilation'' [27], this technique in practice can also be used together with other JIT compilation techniques to achieve an optimal balance point between static and dynamic compilation. Thus we believe this result is of interest to the general audience in the JVM community.
赞助商链接