| Developer(s) | Oracle Corporation (previously Sun Microsystems) |
|---|---|
| Stable release | 20.0-b11 |
| Written in | C++ |
| Operating system | Cross-platform |
| Type | Java Virtual Machine |
| License | GNU General Public License |
| Website | Sun's OpenJDK Hotspot page |
HotSpot is a Java virtual machine for desktops and servers, maintained and distributed by Oracle Corporation. It features techniques such as just-in-time compilation and adaptive optimization designed to improve performance.
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HotSpot, first released April 27, 1999, was originally developed by Longview Technologies, LLC which was doing business as Animorphic, a small startup company formed in 1994. Animorphic's virtual machine technology had earlier been successfully used in a Sun research project, the Self programming language. In 1997, Longview Technologies, LLC (DBA Animorphic) was purchased by Sun Microsystems.[1] Initially available as an add-on for Java 1.2, HotSpot became the default Sun JVM in Java 1.3.[2]
Its name derives from the fact that as it runs Java bytecode, it continually analyzes the program's performance for "hot spots" which are frequently or repeatedly executed. These are then targeted for optimization, leading to high performance execution with a minimum of overhead for less performance-critical code. In some cases, it is possible for adaptive optimization of a JVM to exceed the performance of hand-coded C++ or C code.[3]
Sun's JRE 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, that yield higher performance. Both VMs compile only often-run methods, using a configurable invocation-count-threshold to decide which methods to compile.
The HotSpot Java virtual machine is written in C++. As stated in HotSpot web page, the source contains approximately 250,000 lines of code.[4] Hotspot provides:
The version of HotSpot for Microsoft Windows runs a background process jucheck.exe, which continually checks for updates from Oracle.[5]
HotSpot supports many command-line arguments 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).[6][7][8][9]
On 13 November 2006, the Sun JVM and JDK were licensed[10] under the GPL version 2 (see Sun's OpenJDK Hotspot page). This is the code that became part of Java 7 (codename Dolphin[11]).
As for the whole JDK, HotSpot is supported by Oracle Corporation on Microsoft Windows, Linux, and Solaris. Supported ISAs are IA-32, x86-64 and SPARC (exclusive to Solaris).[12]
Ports are also available by third parties for Mac OS X and various other Unix operating systems. Several different hardware architectures are supported, including x86, PowerPC, and SPARC (Solaris only).
Porting HotSpot is difficult because the code, while primarily written in C++, contains a lot of assembly language.[13] 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 Linux processor architecture. The code of zero-assembler Hotspot is used for all the non-x86 ports of HotSpot (PPC, IA64, S390 and ARM) since version 1.6.[14][15][16]
Gary Benson, an IcedTea developer, developed a platform-independent Just-in-time compiler called Shark for HotSpot, using LLVM, to complement zero.[17][18]
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