[DevoxxPL2022] Bare Metal Java • Jarosław Pałka
Jarosław Pałka, a staff engineer at Neo4j, captivated the audience at Devoxx Poland 2022 with an in-depth exploration of low-level Java programming through the Foreign Function and Memory API. As a veteran of the JVM ecosystem, Jarosław shared his expertise in leveraging these experimental APIs to interact directly with native memory and C code, offering a glimpse into Java’s potential for high-performance, system-level programming. His presentation, blending technical depth with engaging demos, provided a roadmap for developers seeking to harness Java’s evolving capabilities.
The Need for Low-Level Access in Java
Jarosław began by contextualizing the necessity of low-level APIs in Java, a language traditionally celebrated for its managed runtime and safety guarantees. He outlined the trade-offs between safety and performance, noting that managed runtimes abstract complexities like memory management but limit optimization opportunities. In high-performance systems like Neo4j, Kafka, or Elasticsearch, direct memory access is critical to avoid garbage collection overhead. Jarosław introduced the Foreign Function and Memory API, incubated since Java 14 and stabilized in Java 17, as a safer alternative to the sun.misc.Unsafe API, enabling developers to work with native memory while preserving Java’s safety principles.
Mastering Native Memory with Memory Segments
Delving into the API’s mechanics, Jarosław explained the concept of memory segments, which serve as pointers to native memory. These segments, managed through resource scopes, allow developers to allocate and deallocate memory explicitly, with safety mechanisms to prevent unauthorized access across threads. He demonstrated how memory segments support operations like setting and retrieving primitive values, using var handles for type-safe access. Jarosław emphasized the API’s flexibility, enabling seamless interaction with both heap and off-heap memory, and its potential to unify access to diverse memory types, including memory-mapped files and persistent memory.
Bridging Java and C with Foreign Functions
A highlight of Jarosław’s talk was the Foreign Function API, which simplifies calling C functions from Java and vice versa. He showcased a practical example of invoking the getpid C function to retrieve a process ID, illustrating the use of symbol lookups, function descriptors, and method handles to map C types to Java. Jarosław also explored upcalls, allowing C code to invoke Java methods, using a signal handler as a case study. This bidirectional integration eliminates the complexities of Java Native Interface (JNI), streamlining interactions with native libraries like SDL for game development.
Practical Applications: A Java Game Demo
To illustrate the API’s power, Jarosław presented a live demo of a 2D game built using Java and the SDL library. By mapping C structures to Java memory layouts, he created sprites and handled events like keyboard inputs, demonstrating how Java can interface with hardware for real-time rendering. The demo highlighted the challenges of manual structure mapping and memory management, but also showcased the API’s potential to simplify these tasks. Jarosław noted that Java 19’s jextract tool automates this process by generating Java bindings from C header files, significantly reducing boilerplate.
Safety and Performance Considerations
Jarosław underscored the API’s safety features, such as temporal and spatial bounds checking, which prevent invalid memory access. He also discussed the cleaner mechanism, which integrates with Java’s garbage collector to manage native memory deallocation. While the API introduces overhead comparable to JNI, Jarosław highlighted its potential for optimization in future releases, particularly for serverless applications and caching. He cautioned developers to use these APIs judiciously, given their complexity and the need for careful error handling.
Future Prospects and Java’s Evolution
Looking ahead, Jarosław positioned the Foreign Function and Memory API as a transformative step in Java’s evolution, enabling developers to write high-performance applications traditionally reserved for languages like C or Rust. He encouraged exploration of these APIs for niche use cases like database development or game engines, while acknowledging their experimental nature. Jarosław’s vision of Java as a versatile platform for both high-level and low-level programming resonated, urging developers to embrace these tools to push the boundaries of what Java can achieve.