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Java 即時程式設計

在 Realtime Java 領域富有盛名的 [aicas GmbH]，其主力產品為 [JamaicaVM Realtime Java]，該公司部份的工程師也是 [GNU Classpath] 的 developer / committer，產品特徵的 "Libraries compatible with JDK J2SE V1.2 and largely compatible with J2SE 1.3 and J2SE 1.4" 可說是另一項應用 Free / Open Source Softwafre 商業化成功的案例。不過，[aicas GmbH] 最重要的技術當然是 Realtime Java 核心的設計，特別是 Deterministic Garbage Collection 與 Hard Realtime Execution，而該公司的 Dr. James J. Hunt (CEO) 與 Dr. Fridtjof B. Siebert (CTO) 日前於 Embedded.com 發表兩篇短文 [Realtime programming in Java: Part 1] 與 [Realtime programming in Java: Part 2]，篇幅不長，但闡述許多重要概念，很值得參考。

文章一開頭就寫到 [Inadequacies of Java for Realtime Programming]：

There are two main kinds of barriers to using Java for realtime and embedded programming: lack of determinism and limited access to the underlying hardware. Both these issue arise in part from the goal of ensuring platform independence.

所以，將 Java 應用於 Embedded Systems 會面臨 Java Runtime 本身的可預測精確性與對硬體的掌握度這兩個不足處，而在 RTSJ 中規範了 Realtime GC 的具體要求，文章也就 RTSJ 的規範，展示真實應用上的模式，同時，為了掌握硬體，也就 RTSJ 規範的語意，文章給予一個介紹性的案例。

第二篇提到的 [Open Issues] 相當有意思，文章提到：

The RTSJ is an important step in the development of Java technology; however, the specification still has weaknesses. As mentioned above, the size issue is being addressed by the safety critical Java effort. More fundamentally, there are the issues of device access and control transfer. The Java language collection API is also less than ideal in terms of memory consumption.

這也是 Realtime Java Programming 需考慮的重要議題。
由 jserv 發表於 May 25, 2006 08:40 PM