HotSpot, released as Java HotSpot Performance Engine, is a Java virtual machine for

desktop A desktop traditionally refers to: * The surface of a desk (often to distinguish office appliances that fit on a desk, such as photocopiers and printers, from larger equipment covering its own area on the floor) Desktop may refer to various compu ...

and

server Server may refer to: Computing *Server (computing), a computer program or a device that provides functionality for other programs or devices, called clients Role * Waiting staff, those who work at a restaurant or a bar attending customers and su ...

computers, developed by Sun Microsystems and now maintained and distributed by Oracle Corporation. It features improved performance via methods such as

just-in-time compilation In computing, just-in-time (JIT) compilation (also dynamic translation or run-time compilations) is a way of executing computer code that involves compilation during execution of a program (at run time) rather than before execution. This may co ...

and

adaptive optimization Adaptive optimization is a technique in computer science that performs dynamic recompilation of portions of a program based on the current execution profile. With a simple implementation, an adaptive optimizer may simply make a trade-off between ...

History

The Java HotSpot Performance Engine was released on April 27, 1999, built on technologies from an implementation of the programming language Smalltalk named Strongtalk, originally developed by Longview Technologies, which traded as Animorphic. The Longview virtual machine was based on the

Self The self is an individual as the object of that individual’s own reflective consciousness. Since the ''self'' is a reference by a subject to the same subject, this reference is necessarily subjective. The sense of having a self—or ''selfhoo ...

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 Lars Ytting Bak (born 16 January 1980) is a Danish former professional road bicycle racer, who rode professionally between 2002 and 2019 for the Fakta, , , , and squads. From 2022, Bak will act as team manager for UCI Women's WorldTeam . Ba ...

left Sun to start Longview. In 1997, Sun Microsystems purchased Animorphic. Shortly after acquiring Animorphic, Sun decided to write a new just-in-time (JIT) compiler for the Java virtual machine. This new compiler would give rise to the name ''HotSpot'', derived from the software's behavior: as it runs

Java bytecode In computing, Java bytecode is the bytecode-structured instruction set of the Java virtual machine (JVM), a virtual machine that enables a computer to run programs written in the Java programming language and several other programming langua ...

, 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 Mathematical optimization (alternatively spelled ''optimisation'') or mathematical programming is the selection of a best element, with regard to some criterion, from some set of available alternatives. It is generally divided into two subfi ...

, leading to high-performance execution with a minimum of overhead for less performance-critical code. In one report, the JVM beat some

C++ C++ (pronounced "C plus plus") is a high-level general-purpose programming language created by Danish computer scientist Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded significan ...

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

and Assembly. In 2007, Sun estimated it comprised approximately 250,000 lines of source code. Hotspot provides: * A

Java Classloader The Java Class Loader is a part of the Java Runtime Environment that dynamically loads Java classes into the Java Virtual Machine. Usually classes are only loaded on demand. The Java run time system does not need to know about files and file syste ...

* A templating

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

JVM flags

HotSpot supports many

command-line argument A command-line interpreter or command-line processor uses a command-line interface (CLI) to receive commands from a user in the form of lines of text. This provides a means of setting parameters for the environment, invoking executables and pro ...

s for options of the virtual machine execution. Some are standard and must be found in any conforming Java virtual machine; 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 The Java Development Kit (JDK) is a distribution of Java Technology by Oracle Corporation. It implements the Java Language Specification (JLS) and the Java Virtual Machine Specification (JVMS) and provides the Standard Edition (SE) of the Java ...

(JDK) were licensed under the

GNU General Public License The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software licenses that guarantee end users the four freedoms to run, study, share, and modify the software. The license was the first copyleft for general ...

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

Supported platforms

Maintained by Oracle

As with the entire

(JDK), HotSpot is supported by Oracle Corporation on

Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for ser ...

Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, w ...

, and

macOS macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and lapt ...

. Supported instruction set architectures (ISAs) are

x86-64 x86-64 (also known as x64, x86_64, AMD64, and Intel 64) is a 64-bit version of the x86 instruction set, first released in 1999. It introduced two new modes of operation, 64-bit mode and compatibility mode, along with a new 4-level paging ...

and

AArch64 AArch64 or ARM64 is the 64-bit extension of the ARM architecture family. It was first introduced with the Armv8-A architecture. Arm releases a new extension every year. ARMv8.x and ARMv9.x extensions and features Announced in October 2011, AR ...

. Since JDK 15, Solaris and

SPARC SPARC (Scalable Processor Architecture) is a reduced instruction set computer (RISC) instruction set architecture originally developed by Sun Microsystems. Its design was strongly influenced by the experimental Berkeley RISC system develope ...

are no more 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, multiuser 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, an ...

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also i ...

s. Several different hardware architectures are supported, including x86, PowerPC, and SPARC (Solaris only). Porting HotSpot is difficult, as much of it is almost extensively written in assembly language, 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 x86 (also known as 80x86 or the 8086 family) is a family of complex instruction set computer (CISC) instruction set architectures initially developed by Intel based on the Intel 8086 microprocessor and its 8088 variant. The 8086 was intr ...

architecture ports of HotSpot ( PowerPC,

Itanium Itanium ( ) is a discontinued family of 64-bit Intel microprocessors that implement the Intel Itanium architecture (formerly called IA-64). Launched in June 2001, Intel marketed the processors for enterprise servers and high-performance comput ...

(

IA-64 IA-64 (Intel Itanium architecture) is the instruction set architecture (ISA) of the Itanium family of 64-bit Intel microprocessors. The basic ISA specification originated at Hewlett-Packard (HP), and was subsequently implemented by Intel in col ...

S390 The IBM System/390 is a discontinued mainframe product family implementing the ESA/390, the fifth generation of the System/360 instruction set architecture. The first computers to use the ESA/390 were the Enterprise System/9000 (ES/9000) ...

and

ARM In human anatomy, the arm refers to the upper limb in common usage, although academically the term specifically means the upper arm between the glenohumeral joint (shoulder joint) and the elbow joint. The distal part of the upper limb between th ...

) 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