C performance vs Java C

Question

My understanding is that C C   produces native code to run on a particular machine architecture   Conversely  languages like Java and C  run on top of a virtual machine which abstracts away the native architecture   Logically it would seem impossible for Java or C  to match the speed of C   because of this intermediate step  however I ve been told that the latest compilers   hot spot   can attain this speed or even exceed it   Perhaps this is more of a compiler question than a language question  but can anyone explain in plain English how it is possible for one of these virtual machine languages to perform better than a native language

User · Answer

Actually  C  does not really run in a virtual machine like Java does  IL is compiled into assembly language  which is entirely native code and runs at the same speed as native code  You can pre-JIT an  NET application which entirely removes the JIT cost and then you are running entirely native code   The slowdown with  NET will come not because  NET code is slower  but because it does a lot more behind the scenes to do things like garbage collect  check references  store complete stack frames  etc  This can be quite powerful and helpful when building applications  but also comes at a cost  Note that you could do all these things in a C   program as well  much of the core  NET functionality is actually  NET code which you can view in ROTOR   However  if you hand wrote the same functionality you would probably end up with a much slower program since the  NET runtime has been optimized and finely tuned   That said  one of the strengths of managed code is that it can be fully verifiable  ie  you can verify that the code will never access another processes s memory or do unsage things before you execute it  Microsoft has a research prototype of a fully managed operating system that has suprisingly shown that a 100  managed environment can actually perform significantly faster than any modern operating system by taking advantage of this verification to turn off security features that are no longer needed by managed programs  we are talking like 10x in some cases   SE radio has a great episode talking about this project

User · Answer

I don t know either   my Java programs are always slow   -  I ve never really noticed C  programs being particularly slow  though

User · Answer

JIT vs  Static Compiler  As already said in the previous posts  JIT can compile IL bytecode into native code at runtime  The cost of that was mentionned  but not to its conclusion   JIT has one massive problem is that it can t compile everything  JIT compiling takes time  so the JIT will compile only some parts of the code  whereas a static compiler will produce a full native binary  For some kind of programs  the static compiler will simply easily outperform the JIT   Of course  C   or Java  or VB  is usually faster to produce viable and robust solution than is C    if only because C   has complex semantics  and C   standard library  while interesting and powerful  is quite poor when compared with the full scope of the standard library from  NET or Java   so usually  the difference between C   and  NET or Java JIT won t be visible to most users  and for those binaries that are critical  well  you can still call C   processing from C  or Java  even if this kind of native calls can be quite costly in themselves      C   metaprograming  Note that usually  you are comparing C   runtime code with its equivalent in C  or Java  But C   has one feature that can outperform Java C  out of the box  that is template metaprograming  The code processing will be done at compilation time  thus  increasing vastly compilation time   resulting into zero  or almost zero  runtime   I have yet so see a real life effect on this  I played only with concepts  but by then  the difference was seconds of execution for JIT  and zero for C     but this is worth mentioning  alongside the fact template metaprograming is not trivial        Edit 2011-06-10  In C    playing with types is done at compile time  meaning producing generic code which calls non-generic code  e g  a generic parser from string to type T  calling standard library API for types T it recognizes  and making the parser easily extensible by its user  is very easy and very efficient  whereas the equivalent in Java or C  is painful at best to write  and will always be slower and resolved at runtime even when the types are known at compile time  meaning your only hope is for the JIT to inline the whole thing            Edit 2011-09-20  The team behind Blitz    Homepage  Wikipedia  went that way  and apparently  their goal is to reach FORTRAN s performance on scientific calculations by moving as much as possible from runtime execution to compilation time  via C   template metaprogramming  So the  I have yet so see a real life effect on this  part I wrote above apparently does exist in real life    Native C   Memory Usage  C   has a memory usage different from Java C   and thus  has different advantages flaws   No matter the JIT optimization  nothing will go has fast as direct pointer access to memory  let s ignore for a moment processor caches  etc    So  if you have contiguous data in memory  accessing it through C   pointers  i e  C pointers    Let s give Caesar its due  will goes times faster than in Java C   And C   has RAII  which makes a lot of processing a lot easier than in C  or even in Java  C   does not need using to scope the existence of its objects  And C   does not have a finally clause  This is not an error    -   And despite C  primitive-like structs  C    on the stack  objects will cost nothing at allocation and destruction  and will need no GC to work in an independent thread to do the cleaning   As for memory fragmentation  memory allocators in 2008 are not the old memory allocators from 1980 that are usually compared with a GC  C   allocation can t be moved in memory  true  but then  like on a Linux filesystem  Who needs hard disk defragmenting when fragmentation does not happen  Using the right allocator for the right task should be part of the C   developer toolkit  Now  writing allocators is not easy  and then  most of us have better things to do  and for the most of use  RAII or GC is more than good enough      Edit 2011-10-04  For examples about efficient allocators  On Windows platforms  since Vista  the Low Fragmentation Heap is enabled by default  For previous versions  the LFH can be activated by calling the WinAPI function HeapSetInformation   On other OSes  alternative allocators are provided  see https   secure wikimedia org wikipedia en wiki Malloc for a list    Now  the memory model is somewhat becoming more complicated with the rise of multicore and multithreading technology  In this field  I guess  NET has the advantage  and Java  I was told  held the upper ground  It s easy for some  on the bare metal  hacker to praise his  near the machine  code  But now  it is quite more difficult to produce better assembly by hand than letting the compiler to its job  For C    the compiler became usually better than the hacker since a decade  For C  and Java  this is even easier   Still  the new standard C  0x will impose a simple memory model to C   compilers  which will standardize  and thus simplify  effective multiprocessing parallel threading code in C    and make optimizations easier and safer for compilers  But then  we ll see in some couple of years if its promises are held true   C   CLI vs  C  VB NET  Note  In this section  I am talking about C   CLI  that is  the C   hosted by  NET  not the native C     Last week  I had a training on  NET optimization  and discovered that the static compiler is very important anyway  As important than JIT   The very same code compiled in C   CLI  or its ancestor  Managed C    could be times faster than the same code produced in C   or VB NET  whose compiler produces the same IL than C     Because the C   static compiler was a lot better to produce already optimized code than C  s   For example  function inlining in  NET is limited to functions whose bytecode is less or equal than 32 bytes in length  So  some code in C  will produce a 40 bytes accessor  which won t be ever inlined by the JIT  The same code in C   CLI will produce a 20 bytes accessor  which will be inlined by the JIT   Another example is temporary variables  that are simply compiled away by the C   compiler while still being mentioned in the IL produced by the C  compiler  C   static compilation optimization will result in less code  thus authorizes a more aggressive JIT optimization  again   The reason for this was speculated to be the fact C   CLI compiler profited from the vast optimization techniques from C   native compiler   Conclusion  I love C     But as far as I see it  C  or Java are all in all a better bet  Not because they are faster than C    but because when you add up their qualities  they end up being more productive  needing less training  and having more complete standard libraries than C    And as for most of programs  their speed differences  in one way or another  will be negligible     Edit  2011-06-06   My experience on C   NET  I have now 5 months of almost exclusive professional C  coding  which adds up to my CV already full of C   and Java  and a touch of C   CLI    I played with WinForms  Ahem     and WCF  cool    and WPF  Cool     Both through XAML and raw C   WPF is so easy I believe Swing just cannot compare to it   and C  4 0   The conclusion is that while it s easier faster to produce a code that works in C  Java than in C    it s a lot harder to produce a strong  safe and robust code in C   and even harder in Java  than in C    Reasons abound  but it can be summarized by    Generics are not as powerful as templates  try to write an efficient generic Parse method  from string to T   or an efficient equivalent of boost  lexical cast in C  to understand the problem  RAII remains unmatched  GC still can leak  yes  I had to handle that problem  and will only handle memory  Even C  s using is not as easy and powerful because writing a correct Dispose implementations is difficult  C  readonly and Java final are nowhere as useful as C   s const  There s no way you can expose readonly complex data  a Tree of Nodes  for example  in C  without tremendous work  while it s a built-in feature of C    Immutable data is an interesting solution  but not everything can be made immutable  so it s not even enough  by far     So  C  remains an pleasant language as long as you want something that works  but a frustrating language the moment you want something that always and safely works   Java is even more frustrating  as it has the same problems than C   and more  Lacking the equivalent of C  s using keyword  a very skilled colleague of mine spent too much time making sure its resources where correctly freed  whereas the equivalent in C   would have been easy  using destructors and smart pointers    So I guess C  Java s productivity gain is visible for most code    until the day you need the code to be as perfect as possible  That day  you ll know pain   you won t believe what s asked from our server and GUI apps       About Server-side Java and C    I kept contact with the server teams  I worked 2 years among them  before getting back to the GUI team   at the other side of the building  and I learned something interesting   Last years  the trend was to have the Java server apps be destined to replace the old C   server apps  as Java has a lot of frameworks tools  and is easy to maintain  deploy  etc  etc       Until the problem of low-latency reared its ugly head the last months  Then  the Java server apps  no matter the optimization attempted by our skilled Java team  simply and cleanly lost the race against the old  not really optimized C   server   Currently  the decision is to keep the Java servers for common use where performance while still important  is not concerned by the low-latency target  and aggressively optimize the already faster C   server applications for low-latency and ultra-low-latency needs   Conclusion  Nothing is as simple as expected   Java  and even more C   are cool languages  with extensive standard libraries and frameworks  where you can code fast  and have result very soon   But when you need raw power  powerful and systematic optimizations  strong compiler support  powerful language features and absolute safety  Java and C  make it difficult to win the last missing but critical percents of quality you need to remain above the competition   It s as if you needed less time and less experienced developers in C  Java than in C   to produce average quality code  but in the other hand  the moment you needed excellent to perfect quality code  it was suddenly easier and faster to get the results right in C     Of course  this is my own perception  perhaps limited to our specific needs   But still  it is what happens today  both in the GUI teams and the server-side teams   Of course  I ll update this post if something new happens   Edit  2011-06-22       We find that in regards to performance  C   wins out by   a large margin  However  it also required the most extensive   tuning efforts  many of which were done at a level of sophistication   that would not be available to the average programmer             The Java version was probably the simplest to implement  but the hardest to analyze for performance  Specifically the effects around garbage collection were complicated and very hard to tune     Sources    https   days2011 scala-lang org sites days2011 files ws3-1-Hundt pdf http   www computing co uk ctg news 2076322 -winner-google-language-tests   Edit  2011-09-20       The going word at Facebook is that  reasonably written C   code just runs fast   which underscores the enormous effort spent at optimizing PHP and Java code  Paradoxically  C   code is more difficult to write than in other languages  but efficient code is a lot easier  to write in C   than in other languages             Herb Sutter at   build   quoting Andrei Alexandrescu   Sources    http   channel9 msdn com Events BUILD BUILD2011 TOOL-835T http   video ch9 ms build 2011 slides TOOL-835T Sutter pptx

User · Answer

In some cases  managed code can actually be faster than native code  For instance   mark-and-sweep  garbage collection algorithms allow environments like the JRE or CLR to free large numbers of short-lived  usually  objects in a single pass  where most C C   heap objects are freed one-at-a-time   From wikipedia      For many practical purposes  allocation deallocation-intensive algorithms implemented in garbage collected languages can actually be faster than their equivalents using manual heap allocation  A major reason for this is that the garbage collector allows the runtime system to amortize allocation and deallocation operations in a potentially advantageous fashion    That said  I ve written a lot of C  and a lot of C    and I ve run a lot of benchmarks  In my experience  C   is a lot faster than C   in two ways   1  if you take some code that you ve written in C   port it to C   the native code tends to be faster  How much faster  Well  it varies a whole lot  but it s not uncommon to see a 100  speed improvement   2  In some cases  garbage collection can massively slow down a managed application  The  NET CLR does a terrible job with large heaps  say    2GB   and can end up spending a lot of time in GC--even in applications that have few--or even no--objects of intermediate life spans   Of course  in most cases that I ve encounted  managed languages are fast enough  by a long shot  and the maintenance and coding tradeoff for the extra performance of C   is simply not a good one

User · Answer

Whenever I talk managed vs  unmanaged performance  I like to point to the series Rico  and Raymond  did comparing C   and C  versions of a Chinese English dictionary   This google search will let you read for yourself  but I like Rico s summary      So am I ashamed by my crushing defeat    Hardly   The managed code got a very   good result for hardly any effort  To   defeat the managed Raymond had to          Write his own file I O stuff    Write his own string class    Write his own allocator    Write his own international mapping         Of course he used available lower   level libraries to do this  but that s   still a lot of work   Can you call   what s left an STL program   I don t   think so  I think he kept the   std  vector class which ultimately was   never a problem and he kept the find   function   Pretty much everything else   is gone       So  yup  you can definately beat the   CLR   Raymond can make his program go   even faster I think       Interestingly  the time to parse the   file as reported by both programs   internal timers is about the same --   30ms for each   The difference is in   the overhead    For me the bottom line is that it took 6 revisions for the unmanaged version to beat the managed version that was a simple port of the original unmanaged code   If you need every last bit of performance  and have the time and expertise to get it   you ll have to go unmanaged  but for me  I ll take the order of magnitude advantage I have on the first versions over the 33  I gain if I try 6 times

User · Answer

If you re a Java C  programmer learning C    you ll be tempted to keep thinking in terms of Java C  and translate verbatim to C   syntax  In that case  you only get the earlier mentioned benefits of native code vs  interpreted JIT  To get the biggest performance gain in C   vs  Java C   you have to learn to think in C   and design code specifically to exploit the strengths of C     To paraphrase Edsger Dijkstra   your first language  mutilates the mind beyond recovery  To paraphrase Jeff Atwood  you can write  your first language  in any new language

User · Answer

It would only happen if the Java interpreter is producing machine code that is actually better optimized than the machine code your compiler is generating for the C   code you are writing  to the point where the C   code is slower than the Java and the interpretation cost   However  the odds of that actually happening are pretty low - unless perhaps Java has a very well-written library  and you have your own poorly written C   library

User · Answer

Generally  C  and Java can be just as fast or faster because the JIT compiler -- a compiler that compiles your IL the first time it s executed -- can make optimizations that a C   compiled program cannot because it can query the machine  It can determine if the machine is Intel or AMD  Pentium 4  Core Solo  or Core Duo  or if supports SSE4  etc   A C   program has to be compiled beforehand usually with mixed optimizations so that it runs decently well on all machines  but is not optimized as much as it could be for a single configuration  i e  processor  instruction set  other hardware    Additionally certain language features allow the compiler in C  and Java to make assumptions about your code that allows it to optimize certain parts away that just aren t safe for the C C   compiler to do  When you have access to pointers there s a lot of optimizations that just aren t safe   Also Java and C  can do heap allocations more efficiently than C   because the layer of abstraction between the garbage collector and your code allows it to do all of its heap compression at once  a fairly expensive operation    Now I can t speak for Java on this next point  but I know that C  for example will actually remove methods and method calls when it knows the body of the method is empty  And it will use this kind of logic throughout your code   So as you can see  there are lots of reasons why certain C  or Java implementations will be faster   Now this all said  specific optimizations can be made in C   that will blow away anything that you could do with C   especially in the graphics realm and anytime you re close to the hardware  Pointers do wonders here   So depending on what you re writing I would go with one or the other  But if you re writing something that isn t hardware dependent  driver  video game  etc   I wouldn t worry about the performance of C   again can t speak about Java   It ll do just fine   One the Java side   Swati points out a good article   https   www ibm com developerworks library j-jtp09275

User · Answer

Actually  C  does not really run in a virtual machine like Java does  IL is compiled into assembly language  which is entirely native code and runs at the same speed as native code  You can pre-JIT an  NET application which entirely removes the JIT cost and then you are running entirely native code   The slowdown with  NET will come not because  NET code is slower  but because it does a lot more behind the scenes to do things like garbage collect  check references  store complete stack frames  etc  This can be quite powerful and helpful when building applications  but also comes at a cost  Note that you could do all these things in a C   program as well  much of the core  NET functionality is actually  NET code which you can view in ROTOR   However  if you hand wrote the same functionality you would probably end up with a much slower program since the  NET runtime has been optimized and finely tuned   That said  one of the strengths of managed code is that it can be fully verifiable  ie  you can verify that the code will never access another processes s memory or do unsage things before you execute it  Microsoft has a research prototype of a fully managed operating system that has suprisingly shown that a 100  managed environment can actually perform significantly faster than any modern operating system by taking advantage of this verification to turn off security features that are no longer needed by managed programs  we are talking like 10x in some cases   SE radio has a great episode talking about this project

User · Answer

The virtual machine languages are unlikely to outperform compiled languages but they can get close enough that it doesn t matter  for  at least  the following reasons  I m speaking for Java here since I ve never done C     1  The Java Runtime Environment is usually able to detect pieces of code that are run frequently and perform just-in-time  JIT  compilation of those sections so that  in future  they run at the full compiled speed   2  Vast portions of the Java libraries are compiled so that  when you call a library function  you re executing compiled code  not interpreted  You can see the code  in C  by downloading the OpenJDK   3  Unless you re doing massive calculations  much of the time your program is running  it s waiting for input from a very slow  relatively speaking  human   4  Since a lot of the validation of Java bytecode is done at the time of loading the class  the normal overhead of runtime checks is greatly reduced   5  At the worst case  performance-intensive code can be extracted to a compiled module and called from Java  see JNI  so that it runs at full speed   In summary  the Java bytecode will never outperform native machine language  but there are ways to mitigate this  The big advantage of Java  as I see it  is the HUGE standard library and the cross-platform nature

User · Answer

Actually Sun s HotSpot JVM uses  mixed-mode  execution  It interprets the method s bytecode until it determines  usually through a counter of some sort  that a particular block of code  method  loop  try-catch block  etc   is going to be executed a lot  then it JIT compiles it  The time required to JIT compile a method often takes longer than if the method were to be interpreted if it is a seldom run method  Performance is usually higher for  mixed-mode  because the JVM does not waste time JITing code that is rarely  if ever  run  C  and  NET do not do this   NET JITs everything which  often times  wastes time

User · Answer

For anything needing lots of speed  the JVM just calls a C   implementation  so it s a question more of how good their libs are than how good the JVM is for most OS related things  Garbage collection cuts your memory in half  but using some of the fancier STL and Boost features will have the same effect but with many times the bug potential    If you are just using C   libraries and lots of its high level features in a large project with many classes you will probably wind up slower than using a JVM  Except much more error prone   However  the benefit of C   is that it allows you to optimize yourself  otherwise you are stuck with what the compiler jvm does  If you make your own containers  write your own memory management that s aligned  use SIMD  and drop to assembly here and there  you can speed up at least 2x-4x times over what most C   compilers will do on their own  For some operations  16x-32x  That s using the same algorithms  if you use better algorithms and parallelize  increases can be dramatic  sometimes thousands of times faster that commonly used methods

User · Answer

Orion Adrian  let me invert your post to see how unfounded your remarks are  because a lot can be said about C   as well  And telling that Java C  compiler optimize away empty functions does really make you sound like you are not my expert in optimization  because a  why should a real program contain empty functions  except for really bad legacy code  b  that is really not black and bleeding edge optimization   Apart from that phrase  you ranted blatantly about pointers  but don t objects in Java and C  basically work like C   pointers  May they not overlap  May they not be null  C  and most C   implementations  has the restrict keyword  both have value types  C   has reference-to-value with non-null guarantee  What do Java and C  offer               Generally  C and C   can be just as fast or faster because the AOT compiler -- a compiler that compiles your code  before deployment  once and for all  on your high memory many core build server -- can make optimizations that a C  compiled program cannot because it has a ton of time to do so  The compiler can determine if the machine is Intel or AMD  Pentium 4  Core Solo  or Core Duo  or if supports SSE4  etc  and if your compiler does not support runtime dispatch  you can solve for that yourself by deploying a handful of specialized binaries   A C  program is commonly compiled upon running it so that it runs decently well on all machines  but is not optimized as much as it could be for a single configuration  i e  processor  instruction set  other hardware   and it must spend some time first   Features like loop fission  loop inversion  automatic vectorization  whole program optimization  template expansion  IPO  and many more  are very hard to be solved all and completely in a way that does not annoy the end user   Additionally certain language features allow the compiler in C   or C to make assumptions about your code that allows it to optimize certain parts away that just aren t safe for the Java C  compiler to do  When you don t have access to the full type id of generics or a guaranteed program flow there s a lot of optimizations that just aren t safe   Also C   and C do many stack allocations at once with just one register incrementation  which surely is more efficient than Javas and C  allocations as for the layer of abstraction between the garbage collector and your code   Now I can t speak for Java on this next point  but I know that C   compilers for example will  actually remove methods and method calls when it knows the body of the method is empty  it will eliminate common subexpressions  it may try and retry to find optimal register usage  it does not enforce bounds checking  it will autovectorize loops and inner loops and will invert inner to outer  it moves conditionals out of loops  it splits and unsplits loops  It will expand std  vector into native zero overhead arrays as you d do the C way  It will do inter procedural optimmizations  It will construct return values directly at the caller site  It will fold and propagate expressions  It will reorder data into  a cache friendly manner  It will do jump threading  It lets you write compile time ray tracers with zero runtime overhead   It will make very expensive graph based optimizations  It will do strength reduction  were it replaces certain codes with syntactically totally unequal but semantically equivalent code  the old  xor foo  foo  is just the simplest  though outdated optimization of such kind   If you kindly ask it  you may omit IEEE floating point standards and enable even more optimizations like floating point operand re-ordering  After it has massaged and massacred your code  it might repeat the whole process  because often  certain optimizations lay the foundation for even certainer optimizations  It might also just retry with shuffled parameters and see how the other variant scores in its internal ranking  And it will use this kind of logic throughout your code   So as you can see  there are lots of reasons why certain C   or C implementations will be faster   Now this all said  many optimizations can be made in C   that will blow away anything that you could do with C    especially in the number crunching  realtime and close-to-metal realm  but not exclusively there  You don t even have to touch a single pointer to come a long way   So depending on what you re writing I would go with one or the other  But if you re writing something that isn t hardware dependent  driver  video game  etc   I wouldn t worry about the performance of C   again can t speak about Java   It ll do just fine    lt  lt  lt  lt  lt  lt  lt  lt  lt  lt   Generally  certain generalized arguments might sound cool in specific posts  but don t generally sound certainly credible   Anyways  to make peace  AOT is great  as is JIT  The only correct answer can be  It depends  And the real smart people know that you can use the best of both worlds anyways

User · Answer

Some good answers here about the specific question you asked   I d like to step back and look at the bigger picture   Keep in mind that your user s perception of the speed of the software you write is affected by many other factors than just how well the codegen optimizes   Here are some examples    Manual memory management is hard to do correctly  no leaks   and even harder to do effeciently  free memory soon after you re done with it    Using a GC is  in general  more likely to produce a program that manages memory well   Are you willing to work very hard  and delay delivering your software  in an attempt to out-do the GC  My C  is easier to read  amp  understand than my C     I also have more ways to convince myself that my C  code is working correctly   That means I can optimize my algorithms with less risk of introducing bugs  and users don t like software that crashes  even if it does it quickly   I can create my software faster in C  than in C     That frees up time to work on performance  and still deliver my software on time  It s easier to write good UI in C  than C    so I m more likely to be able to push work to the background while UI stays responsive  or to provide progress or hearbeat UI when the program has to block for a while   This doesn t make anything faster  but it makes users happier about waiting    Everything I said about C  is probably true for Java  I just don t have the experience to say for sure

User · Answer

On top of what some others have said  from my understanding  NET and Java are better at memory allocation  E g  they can compact memory as it gets fragmented while C   cannot  natively  but it can if you re using a clever garbage collector

User · Answer

I don t know either   my Java programs are always slow   -  I ve never really noticed C  programs being particularly slow  though

User · Answer

One of the most significant JIT optimizations is method inlining  Java can even inline virtual methods if it can guarantee runtime correctness  This kind of optimization usually cannot be performed by standard static compilers because it needs whole-program analysis  which is hard because of separate compilation  in contrast  JIT has all the program available to it   Method inlining improves other optimizations  giving larger code blocks to optimize   Standard memory allocation in Java C  is also faster  and deallocation  GC  is not much slower  but only less deterministic

User · Answer

Here is another intersting benchmark  which you can try yourself on your own computer    It compares ASM  VC    C   Silverlight  Java applet  Javascript  Flash  AS3   Roozz plugin speed demo  Please note that the speed of javascript varries a lot depending on what browser is executing it  The same is true for Flash and Silverlight because these plugins run in the same process as the hosting browser  But the Roozz plugin run standard  exe files  which run in their own process  thus the speed is not influenced by the hosting browser

User · Answer

A very short answer  Given a fixed budget you will achieve better performing java application than a C   application  ROI considerations   In addition Java platform has more decent profilers  that will help you pinpoint your hotspots more quickly

User · Answer

One of the most significant JIT optimizations is method inlining  Java can even inline virtual methods if it can guarantee runtime correctness  This kind of optimization usually cannot be performed by standard static compilers because it needs whole-program analysis  which is hard because of separate compilation  in contrast  JIT has all the program available to it   Method inlining improves other optimizations  giving larger code blocks to optimize   Standard memory allocation in Java C  is also faster  and deallocation  GC  is not much slower  but only less deterministic

User · Answer

Here s an interesting benchmark http   zi fi shootout

User · Answer

Generally  your program s algorithm will be much more important to the speed of your application than the language   You can implement a poor algorithm in any language  including C     With that in mind  you ll generally be able to write code the runs faster in a language that helps you implement a more efficient algorithm     Higher-level languages do very well at this by providing easier access to many efficient pre-built data structures and encouraging practices that will help you avoid inefficient code   Of course  they can at times also make it easy to write a bunch of really slow code  too  so you still have to know your platform   Also  C   is catching up with  new   note the quotes  features like the STL containers  auto pointers  etc -- see the boost library  for example   And you might occasionally find that the fastest way to accomplish some task requires a technique like pointer arithmetic that s forbidden in a higher-level language -- though they typcially allow you to call out to a library written in a language that can implement it as desired   The main thing is to know the language you re using  it s associated API  what it can do  and what it s limitations are

User · Answer

The executable code produced from a Java or C  compiler is not interpretted -- it is compiled to native code  just in time   JIT    So  the first time code in a Java C  program is encountered during execution  there is some overhead as the  runtime compiler   aka JIT compiler  turns the byte code  Java  or IL code  C   into native machine instructions   However  the next time that code is encountered while the application is still running  the native code is executed immediately   This explains how some Java C  programs appear to be slow initially  but then perform better the longer they run   A good example is an ASP Net web site   The very first time the web site is accessed  it may be a bit slower as the C  code is compiled to native code by the JIT compiler   Subsequent accesses result in a much faster web site -- server and client side caching aside

User · Answer

Whenever I talk managed vs  unmanaged performance  I like to point to the series Rico  and Raymond  did comparing C   and C  versions of a Chinese English dictionary   This google search will let you read for yourself  but I like Rico s summary      So am I ashamed by my crushing defeat    Hardly   The managed code got a very   good result for hardly any effort  To   defeat the managed Raymond had to          Write his own file I O stuff    Write his own string class    Write his own allocator    Write his own international mapping         Of course he used available lower   level libraries to do this  but that s   still a lot of work   Can you call   what s left an STL program   I don t   think so  I think he kept the   std  vector class which ultimately was   never a problem and he kept the find   function   Pretty much everything else   is gone       So  yup  you can definately beat the   CLR   Raymond can make his program go   even faster I think       Interestingly  the time to parse the   file as reported by both programs   internal timers is about the same --   30ms for each   The difference is in   the overhead    For me the bottom line is that it took 6 revisions for the unmanaged version to beat the managed version that was a simple port of the original unmanaged code   If you need every last bit of performance  and have the time and expertise to get it   you ll have to go unmanaged  but for me  I ll take the order of magnitude advantage I have on the first versions over the 33  I gain if I try 6 times

User · Answer

Actually Sun s HotSpot JVM uses  mixed-mode  execution  It interprets the method s bytecode until it determines  usually through a counter of some sort  that a particular block of code  method  loop  try-catch block  etc   is going to be executed a lot  then it JIT compiles it  The time required to JIT compile a method often takes longer than if the method were to be interpreted if it is a seldom run method  Performance is usually higher for  mixed-mode  because the JVM does not waste time JITing code that is rarely  if ever  run  C  and  NET do not do this   NET JITs everything which  often times  wastes time

User · Answer

You might get short bursts when Java or CLR is faster than C    but overall the performance is worse for the life of the application  see www codeproject com KB dotnet RuntimePerformance aspx for some results for that

User · Answer

Here is answer from Cliff Click  http   www azulsystems com blog cliff 2009-09-06-java-vs-c-performanceagain

User · Answer

Here s an interesting benchmark http   zi fi shootout

User · Answer

Go read about HP Labs  Dynamo  an interpreter for PA-8000 that runs on PA-8000  and often runs programs faster than they do natively   Then it won t seem at all surprising   Don t think of it as an  intermediate step  -- running a program involves lots of other steps already  in any language   It often comes down to    programs have hot-spots  so even if you re slower running 95  of the body of code you have to run  you can still be performance-competitive if you re faster at the hot 5  a HLL knows more about your intent than a LLL like C C    and so can generate more optimized code  OCaml has even more  and in practice is often even faster  a JIT compiler has a lot of information that a static compiler doesn t  like  the actual data you happen to have this time  a JIT compiler can do optimizations at run-time that traditional linkers aren t really allowed to do  like reordering branches so the common case is flat  or inlining library calls    All in all  C C   are pretty lousy languages for performance  there s relatively little information about your data types  no information about your data  and no dynamic runtime to allow much in the way of run-time optimization

User · Answer

The compile for specific CPU optimizations are usually overrated   Just  take a program in C   and compile with   optimization for pentium PRO  and run on a pentium 4  Then  recompile with optimize for pentium 4  I passed long afternoons doing it with several programs   General results   Usually less than 2-3  performance increase  So the theoretical JIT advantages  are almost none  Most differences of performance can only be observed when using scalar data processing features  something that  will eventually need manual fine tunning to achieve maximum performance anyway  Optimizations of that sort are slow and costly to perform making them sometimes unsuitable for JIT anyway   On real world and real application C   is still usually faster than java  mainly  because of  lighter memory footprint that result in better cache performance   But to use all of C   capability you  the developer must work hard  You can achieve superior results  but you must use your brain for that  C   is a language that decided to present you with more tools  charging the price that you must  learn them to be able to use the language well

User · Answer

You should define  perform better than     Well  I know  you asked about speed  but its not everything that counts    Do virtual machines perform more runtime overhead  Yes  Do they eat more working memory  Yes  Do they have higher startup costs  runtime initialization and JIT compiler    Yes  Do they require a huge library installed  Yes    And so on  its biased  yes     With C  and Java you pay a price for what you get  faster coding  automatic memory management  big library and so on   But you have not much room to haggle about the details  take the complete package or nothing   Even if those languages can optimize some code to execute faster than compiled code  the whole approach is  IMHO  inefficient  Imagine driving every day 5 miles to your workplace  with a truck  Its comfortable  it feels good  you are safe  extreme crumple zone  and after you step on the gas for some time  it will even be as fast as a standard car  Why don t we all have a truck to drive to work      In C   you get what you pay for  not more  not less   Quoting Bjarne Stroustrup   C   is my favorite garbage collected language because it generates so little garbage  link text

User · Answer

My understanding is that C C   produces native code to run on a particular machine architecture  Conversely  languages like Java and C  run on top of a virtual machine which abstracts away the native architecture  Logically it would seem impossible for Java or C  to match the speed of C   because of this intermediate step  however I ve been told that the latest compilers   hot spot   can attain this speed or even exceed it    That is illogical  The use of an intermediate representation does not inherently degrade performance  For example  llvm-gcc compiles C and C   via LLVM IR  which is a virtual infinite-register machine  to native code and it achieves excellent performance  often beating GCC       Perhaps this is more of a compiler question than a language question  but can anyone explain in plain English how it is possible for one of these virtual machine languages to perform better than a native language    Here are some examples    Virtual machines with JIT compilation facilitate run-time code generation  e g  System Reflection Emit on  NET  so you can compile generated code on-the-fly in languages like C  and F  but must resort to writing a comparatively-slow interpreter in C or C    For example  to implement regular expressions  Parts of the virtual machine  e g  the write barrier and allocator  are often written in hand-coded assembler because C and C   do not generate fast enough code  If a program stresses these parts of a system then it could conceivably outperform anything that can be written in C or C    Dynamic linking of native code requires conformance to an ABI that can impede performance and obviates whole-program optimization whereas linking is typically deferred on VMs and can benefit from whole-program optimizations  like  NET s reified generics     I d also like to address some issues with paercebal s highly-upvoted answer above  because someone keeps deleting my comments on his answer  that presents a counter-productively polarized view      The code processing will be done at compilation time      Hence template metaprogramming only works if the program is available at compile time which is often not the case  e g  it is impossible to write a competitively performant regular expression library in vanilla C   because it is incapable of run-time code generation  an important aspect of metaprogramming          playing with types is done at compile time   the equivalent in Java or C  is painful at best to write  and will always be slower and resolved at runtime even when the types are known at compile time    In C   that is only true of reference types and is not true for value types      No matter the JIT optimization  nothing will go has fast as direct pointer access to memory   if you have contiguous data in memory  accessing it through C   pointers  i e  C pointers    Let s give Caesar its due  will goes times faster than in Java C     People have observed Java beating C   on the SOR test from the SciMark2 benchmark precisely because pointers impede aliasing-related optimizations   Also worth noting that  NET does type specialization of generics across dynamically-linked libraries after linking whereas C   cannot because templates must be resolved before linking  And obviously the big advantage generics have over templates is comprehensible error messages

User · Answer

I look at it from a few different points    Given infinite time and resources  will managed or unmanaged code be faster   Clearly  the answer is that unmanaged code can always at least tie managed code in this aspect - as in the worst case  you d just hard-code the managed code solution  If you take a program in one language  and directly translate it to another  how much worse will it perform   Probably a lot  for any two languages   Most languages require different optimizations and have different gotchas   Micro-performance is often a lot about knowing these details  Given finite time and resources  which of two languages will produce a better result   This is the most interesting question  as while a managed language may produce slightly slower code  given a program reasonably written for that language   that version will likely be done sooner  allowing for more time spent on optimization

User · Answer

I don t think performance need to considered with respect to processing speed of the server these days  after all the muti-core processor are into market   It should be more defined based on the memory usage  And that way java has a slight disadvantage   But still all in all programing language are suited for different purpose  And that is their competitive area  at each section it is different winners  And I am sure Java will win in the long run for it continues development and competitiveness it shows in all the new features it produce  I found a link here that will support my reason for voting for java

User · Answer

I like Orion Adrian s answer  but there is another aspect to it   The same question was posed decades ago about assembly language vs   human  languages like FORTRAN  And part of the answer is similar   Yes  a C   program is capable of being faster than C  on any given  non-trivial   algorithm  but the program in C  will often be as fast or faster than a  naive  implementation in C    and an optimized version in C   will take longer to develop  and might still beat the C  version by a very small margin  So  is it really worth it   You ll have to answer that question on a one-by-one basis   That said  I m a long time fan of C    and I think it s an incredibly expressive and powerful language -- sometimes underappreciated  But in many  real life  problems  to me personally  that means  the kind I get paid to solve    C  will get the job done sooner and safer   The biggest penalty you pay  Many  NET and Java programs are memory hogs  I have seen  NET and Java apps take  hundreds  of megabytes of memory  when C   programs of similar complexity barely scratch the  tens  of MBs

User · Answer

I m not sure how often you ll find that Java code will run faster than C    even with Hotspot  but I ll take a swing at explaining how it could happen   Think of compiled Java code as interpreted machine language for the JVM   When the Hotspot processor notices that certain pieces of the compiled code are going to be used many times  it performs an optimization on the machine code   Since hand-tuning Assembly is almost always faster than C   compiled code  it s ok to figure that programmatically-tuned machine code isn t going to be too bad   So  for highly repetitious code  I could see where it d be possible for Hotspot JVM to run the Java faster than C      until garbage collection comes into play

User · Answer

JIT  Just In Time Compiling  can be incredibly fast because it optimizes for the target platform   This means that it can take advantage of any compiler trick your CPU can support  regardless of what CPU the developer wrote the code on   The basic concept of the  NET JIT works like this  heavily simplified    Calling a method for the first time    Your program code calls a method Foo   The CLR looks at the type that implements Foo   and gets the metadata associated with it From the metadata  the CLR knows what memory address the IL  Intermediate byte code  is stored in  The CLR allocates a block of memory  and calls the JIT  The JIT compiles the IL into native code  places it into the allocated memory  and then changes the function pointer in Foo   s type metadata to point to this native code  The native code is ran    Calling a method for the second time    Your program code calls a method Foo   The CLR looks at the type that implements Foo   and finds the function pointer in the metadata  The native code at this memory location is ran    As you can see  the 2nd time around  its virtually the same process as C    except with the advantage of real time optimizations   That said  there are still other overhead issues that slow down a managed language  but the JIT helps a lot

[c#] C++ performance vs. Java/C#

Examples related to c#

Examples related to java

Examples related to c++

Examples related to performance

Examples related to bytecode