HotSpot VM

mention HotSpot VM, Believe in all Java Programmers know that , It is Sun JDK and OpenJDK The virtual machine in , It's also At present, the most widely used Java virtual machine . But not everyone knows that , This looks like “ Pure blood ” In the beginning, the virtual machine of Sun Companies to develop , But by a family called “Longview Technologies” Designed by a small company ; Even this virtual machine was not originally for Java Developed by language , It comes from Strongtalk VM, And a lot of technology in this virtual machine comes from a support Self Language implementation “ achieve C Language 50% The above implementation efficiency ” The goal of virtual machine design ,Sun The company noticed that the virtual machine is in JIT There are many excellent ideas and practical effects in compiling , stay 1997 Years acquired Longview Technologies company , So we get HotSpot VM.

HotSpot VM  Both inherited Sun Advantages of the previous two commercial virtual machines （ As mentioned earlier, accurate memory management ）, There are also many new technological advantages of its own , As in its name HotSpot It refers to its hot code detection technology （ In fact, two VM Basically independent products of the same period ,HotSpot A little earlier ,HotSpot It's the exact formula from the beginning GC, and Exact VM There's also a relationship with HotSpot Almost the same hot spot detection . in order to Exact VM and HotSpot VM Which one becomes Sun Mainly supported by VM product , stay Sun There have been arguments within the company ,HotSpot beat Exact It's not a technical victory ）,HotSpot VM The hotspot code detection capability of can find out the most valuable compiled code through the execution counter , And then inform JIT The compiler compiles in method units . If a method is called frequently , Or there are many effective cycles in the method , Will trigger standard compilation and OSR（ Stack replacement ） Compile action . Work properly with the interpreter through the compiler , You can balance optimal program response time with optimal execution performance , And you don't have to wait for the local code output to execute the program , The time pressure of real-time compilation is also relatively reduced , This helps introduce more code optimization techniques , Output higher quality local code .

stay 2006 Year of JavaOne At the conference ,Sun The company announced that it would eventually Java Open source , And in the following year , In succession JDK Every part of （ Of course, it also includes HotSpot VM） stay GPL Open source code under the agreement , And on this basis established OpenJDK. such ,HotSpot VM It becomes Sun JDK and OpenJDK Two very close to each other JDK The common virtual machine of the project .

stay 2008 Years and 2009 year ,Oracle The company acquired BEA Company and Sun company , such Oracle At the same time, we have two excellent Java virtual machine ：JRockit VM and HotSpot VM.Oracle The company announced that in the near future （ It should be released about JDK 8 When ） Will complete the integration of these two virtual machines , Make it complementary . The way of integration is basically HotSpot On the basis of , transplant JRockit Excellent characteristics of , For example, use JRockit The garbage collector and MissionControl service , Use HotSpot Of JIT Compiler and hybrid runtime system .