Sun Microsystems 2 manual Resource Management Mechanisms, Reservation

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The Java Wireless Client software solves this problem by providing a set of resource management mechanisms that can be used to control how resources are allocated. The Java Wireless Client software also provides a set of resource management policies that determine how the system behaves under certain conditions. These policies can be customized to tailor the behavior of the system for a particular deployment. Two example policies are also provided as a starting point for customization. Finally, the implementation of resource mechanisms and policies resides with the resource manager.

Resource Management Mechanisms

Java Wireless Client software has three resource management mechanisms: reservation, limit, and revocation.

Reservation

The reservation mechanism sets aside a certain amount of a resource for a MIDlet and keeps it available for that MIDlet and that MIDlet alone, regardless of whether the MIDlet is using it at the moment. The reserved resource is never granted to another MIDlet. If another MIDlet attempts to allocate the resource, it might fail, even if the first MIDlet is not using all of its reservation.

Assume the heap memory available is 600 kilobytes, MIDlet A has a reservation of 400 kilobytes, but is currently using 250 kilobytes. 350 kilobytes of heap is unused. However, only 200 kilobytes is actually available, because 150 kilobytes of the unused heap is still reserved for MIDlet A. If MIDlet B starts and attempts to allocate 300 kilobytes of heap, it receives an out-of-memory error.

The reservation mechanism improves predictability and helps to prevent data corruption.

MIDlets allocate and free resources (particularly memory) throughout their operation. During a resource shortage, any allocation attempt might fail. These failures might occur at an arbitrary time, even in the midst of an operation. If MIDlet is provided with a reservation and is designed never to exceed this reservation, then its allocation attempts will never fail. Instead, the resources for the reservation are allocated at the time the MIDlet is started.

If there is a resource shortage, the failure will occur at startup time. Once the MIDlet has been started, it is guaranteed not to fail because of a resource shortage. This improves predictability because resource allocation failure occur only at startup time, not at arbitrary times while the MIDlet is running.

22 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 MIDletScheduling the CPU Default PolicyAlternative Policies and Their Implementations 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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