HotSpot, released as Java HotSpot Performance Engine, is a

Java virtual machine A Java virtual machine (JVM) is a virtual machine that enables a computer to run Java programs as well as programs written in other languages that are also compiled to Java bytecode. The JVM is detailed by a specification that formally descr ...

for desktop and server computers, developed by

Sun Microsystems Sun Microsystems, Inc., often known as Sun for short, was an American technology company that existed from 1982 to 2010 which developed and sold computers, computer components, software, and information technology services. Sun contributed sig ...

which was purchased by and became a division of

Oracle Corporation Oracle Corporation is an American Multinational corporation, multinational computer technology company headquartered in Austin, Texas. Co-founded in 1977 in Santa Clara, California, by Larry Ellison, who remains executive chairman, Oracle was ...

in 2010. Its features improved performance via methods such as just-in-time compilation and adaptive optimization. It is the de facto Java Virtual Machine, serving as the reference implementation of the

Java programming language Java is a high-level, general-purpose, memory-safe, object-oriented programming language. It is intended to let programmers ''write once, run anywhere'' ( WORA), meaning that compiled Java code can run on all platforms that support Jav ...

History

The Java HotSpot Performance Engine was released on April 27, 1999, built on technologies from an implementation of the programming language

Smalltalk Smalltalk is a purely object oriented programming language (OOP) that was originally created in the 1970s for educational use, specifically for constructionist learning, but later found use in business. It was created at Xerox PARC by Learni ...

named Strongtalk, originally developed by Longview Technologies, which traded as Animorphic. The Longview virtual machine was based on the

Self In philosophy, the self is an individual's own being, knowledge, and values, and the relationship between these attributes. The first-person perspective distinguishes selfhood from personal identity. Whereas "identity" is (literally) same ...

virtual machine, with an interpreter replacing the fast-and-dumb first compiler. When Sun cancelled the Self project, two key people, Urs Hölzle and Lars Bak left Sun to start Longview. In 1997,

purchased Animorphic. Shortly after acquiring Animorphic, Sun decided to write a new stronger just-in-time (JIT) compiler for the Java virtual machine, named HotSpot server compiler (internal name C2), which was initially developed by Clifford Click and was an extension of his PhD thesis on optimizing compilers. The compiler name ''HotSpot'' is derived from the software's behavior: as it runs

Java bytecode Java bytecode is the instruction set of the Java virtual machine (JVM), the language to which Java and other JVM-compatible source code is compiled. Each instruction is represented by a single byte, hence the name bytecode, making it a compact ...

, as with the Self VM, HotSpot continually analyzes the program's performance for '' hot spots'' which are executed often or repeatedly. These are then targeted for optimizing, leading to high-performance execution with a minimum of overhead for less performance-critical code. In one report, the JVM beat some C++ or C code in some benchmarks. Initially available as an add-on for Java 1.2, HotSpot became the default Sun JVM in Java 1.3.

Features

JRE (originally from Sun, now from Oracle) features two virtual machines, one called ''Client'' and the other ''Server''. The Client version is tuned for quick loading. It makes use of interpretation. The Server version loads more slowly, putting more effort into producing highly optimized JIT compilations to yield higher performance. Both VMs compile only often-run methods, using a configurable invocation-count threshold to decide which methods to compile. Tiered compiling, an option introduced in Java 7, uses both the client and server compilers in tandem to provide faster startup time than the server compiler, but similar or better peak performance. Starting in Java 8, tiered compilation is the default for the server VM. HotSpot is written in C++ and Assembly. In 2007, Sun estimated it comprised approximately 250,000 lines of source code. Hotspot provides: * A Java class loader * A templating

interpreter * ''Client'' (C1) and ''Server'' (C2) Just-in Time Compilers, optimized for their respective uses * Several garbage collectors (including the low-latency ZGC and low-pause-time Shenandoah) * A set of supporting runtime libraries * Serviceability features

JVM flags

HotSpot supports many command-line arguments for options of the virtual machine execution. Some are standard and must be found in any conforming

; others are specific to HotSpot and may not be found in other JVMs (options that begin with -X or -XX are non-standard).

License

On 13 November 2006, the HotSpot JVM and the Java Development Kit (JDK) were licensed under the

GNU General Public License The GNU General Public Licenses (GNU GPL or simply GPL) are a series of widely used free software licenses, or ''copyleft'' licenses, that guarantee end users the freedom to run, study, share, or modify the software. The GPL was the first ...

(GPL) version 2. This is the code that became part of Java 7.JDK7
, Sun.

Supported platforms

Maintained by Oracle

As with the entire Java Development Kit (JDK), HotSpot is supported by

Windows Windows is a Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sec ...

Linux Linux ( ) is a family of open source Unix-like operating systems based on the Linux kernel, an kernel (operating system), operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically package manager, pac ...

, and

macOS macOS, previously OS X and originally Mac OS X, is a Unix, Unix-based operating system developed and marketed by Apple Inc., Apple since 2001. It is the current operating system for Apple's Mac (computer), Mac computers. With ...

. Supported

instruction set In computer science, an instruction set architecture (ISA) is an abstract model that generally defines how software controls the CPU in a computer or a family of computers. A device or program that executes instructions described by that ISA, s ...

architectures (ISAs) are

x86-64 x86-64 (also known as x64, x86_64, AMD64, and Intel 64) is a 64-bit extension of the x86 instruction set architecture, instruction set. It was announced in 1999 and first available in the AMD Opteron family in 2003. It introduces two new ope ...

and

AArch64 AArch64, also known as ARM64, is a 64-bit version of the ARM architecture family, a widely used set of computer processor designs. It was introduced in 2011 with the ARMv8 architecture and later became part of the ARMv9 series. AArch64 allows ...

. Since JDK 15, Solaris and SPARC are no longer supported.

Ports by third parties

Ports are also available by third parties for various other

Unix Unix (, ; trademarked as UNIX) is a family of multitasking, multi-user computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, a ...

operating system An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ...

s. Several different hardware architectures are supported, including x86,

PowerPC PowerPC (with the backronym Performance Optimization With Enhanced RISC – Performance Computing, sometimes abbreviated as PPC) is a reduced instruction set computer (RISC) instruction set architecture (ISA) created by the 1991 Apple Inc., App ...

, and SPARC (Solaris only). Porting HotSpot is difficult, as much of it is almost extensively written in

assembly language In computing, assembly language (alternatively assembler language or symbolic machine code), often referred to simply as assembly and commonly abbreviated as ASM or asm, is any low-level programming language with a very strong correspondence bet ...

, though several sections of it are also written in purely standards conformant ISO C++. To remedy this, the IcedTea project has developed a generic port of the HotSpot interpreter called ''zero-assembler Hotspot'' (or ''zero''), with almost no assembly code. This port is intended for easy adaptation of the interpreter component of HotSpot to any

processor architecture. The code of ''zero-assembler Hotspot'' is used for all the non- x86 architecture ports of HotSpot (

, Itanium ( IA-64), S390 and ARM) since version 1.6.

References

External links

*
A list of HotSpot VMOptions

The Java Virtual Machine Specification

*
HotSpot Mercurial source code development repository (version control system) for JDK8
{{DEFAULTSORT:Hotspot Assembly language software Free software programmed in C++ Java virtual machine Oracle software Sun Microsystems software