Sun Microsystems 2 manual Multitasking

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Multitasking

The Connected Limited Device Configuration HotSpot™ Implementation can run multiple Java applications within a single operating system (OS) process. Historically, a CLDC virtual machine (VM) could run one Java application at a time, and each virtual machine typically required its own OS process. Running more than one Java application meant running more than one OS process. This could use too many resources on some small devices. The multitasking feature enables a single virtual machine, in a single OS process, to function as multiple virtual machines. From the standpoint of each Java application, it is running in a separate virtual machine.

When a MIDlet exits or encounters an error, it always leaves the virtual machine in a consistent state. This works because each MIDlet is isolated from other MIDlets that might also be running at the same time. If the MIDlets were not isolated from each other, an error in one MIDlet might be visible to other MIDlets. This might result in deadlock or crashes caused by corrupted data structures.

Multitasking, then, runs multiple logical virtual machines within a single OS process. The CLDC HotSpot Implementation enables this by providing fundamental mechanisms in the virtual machine. Mechanisms include threads, the isolation of objects in the Java runtime environment (Java objects) belonging to different programs, and safe termination. See the CLDC HotSpot Implementation Virtual Machine White Paper at http://java.sun.com/j2me/docs/pdf/CLDC- HI_whitepaper-February_2005.pdffor more information.

The OS mechanisms are important and necessary, but they aren’t sufficient to provide a complete application environment. A complete system needs mechanisms for managing the application life cycle (starting, stopping, and switching between applications) and for enabling the user to control the application life cycle. It also needs mechanisms for managing competition for limited shared resources, such as memory and network sockets, among multiple applications. The Java Wireless Client software provides all of these additional mechanisms.

The Java Wireless Client software is a high-performance, feature-rich, deployment- ready implementation of Java Technology for the Wireless Industry that takes advantage of the multitasking functionality in the CLDC HotSpot Implementation.

The logical virtual machines in the Java Wireless Client software are called tasks. Each application has its own task. The Application Management System (AMS) runs at all times in its own task. This architecture provides improved performance and robustness.

2 Multitasking Guide • May 2007

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Contents Multitasking Guide Page Contents Glossary Index Code Samples Vi Multitasking Guide May Tables Viii Multitasking Guide May Preface Before You Read This GuideHow This Guide Is Organized Related DocumentationTypographic Conventions Used in This Guide AaBbCc123Accessing Sun Documentation Online Sun Welcomes Your CommentsIntroduction Multitasking Robustness Mechanisms Compared With PoliciesMultitasking Guide May Multitasking Safety Multitask Safety and Multithread Safety Global and Static Data Singletons Multitasking Safety Example Code Example 2-1Native API for a Microwave OvenTypical usage of this API is shown in Code Example Multithread Safety Code Example 2-5Using the Locking Mechanism Multitask Safety Code Example 2-7Migrating Initialization to Native Code Establishing Per-Task Context Code Example 2-8Keeping State in Java Code Code Example 2-9Implementing the Native ncook Method Kniexport Knireturntypeint Multitasking Safety Multitasking Guide May Managing Native Resources Resource Management Mechanisms ReservationLimit Default Resource Allocation Policies RevocationCustomization of Resource Allocation Policies Maximum number of tasks isolates allowed Managing Native Resources Multitasking Guide May Other Multitasking Issues Switching the Foreground MIDletAlternative Policies and Their Implementations Default PolicyScheduling the CPU Default CPU Scheduling Policy Default User Notification Policies Interrupting the UserGlossary Java Community ProcessTM Jcptm Glossary Sun Java Device Test Index Multitasking Guide May
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Sun Microsystems, founded in 1982, was a significant player in the computing industry, best known for its innovative technology solutions and workstations, particularly the Sun-4, which represented a key milestone in the company's history. The Sun-4 architecture, launched in 1987, utilized the SPARC (Scalable Processor Architecture) RISC processor, notable for its high performance and scalability.

One of the primary features of Sun Microsystems' platforms was their ability to efficiently handle multitasking and resource management, making them ideal for enterprise-level applications and development environments. Sun-4 workstations boasted impressive graphics capabilities with the addition of advanced graphical user interfaces, support for color displays, and the SUNVIEW windowing system, which enhanced user experience and productivity.

The Sun-4 systems also supported the SunOS operating system, which was based on UNIX. This operating system was engineered for stability and robustness, offering features like multiuser support, networked environments, and advanced security options. Moreover, SunOS provided seamless integration with various programming languages, including C and C++, facilitating software development that aligned with industry standards.

Another standout characteristic of Sun Microsystems was its commitment to open systems and standards. By providing developers with comprehensive tools and environments, such as the Standardized Application Programming Interface (API) and support for networking protocols, Sun facilitated interoperability among different computing platforms. The emphasis on open architecture also meant that customers could easily upgrade their systems without being locked into proprietary solutions.

Sun Microsystems was also ahead of its time with innovations in network computing. Their workstations were among the first to support network file systems and distributed computing concepts, enabling seamless data sharing across multiple systems. With the introduction of the Network File System (NFS), Sun revolutionized how data was accessed and managed across networks, which played a significant role in the evolving landscape of client-server computing.

In summary, the Sun Microsystems 2 and its successive innovations in workstation technology highlighted the company's forward-thinking approach. By integrating powerful performance with open systems, robust operating systems, and advanced networking capabilities, Sun laid the groundwork for modern computing, influencing various sectors from academia to enterprise solutions. Even after its acquisition by Oracle in 2010, the legacy of Sun Microsystems continues to be felt across the computing industry.
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