The blog post explores how C, despite lacking built-in object-oriented features like polymorphism, achieves similar functionality through clever struct design and function pointers. It uses examples from the Linux kernel and FFmpeg to demonstrate this. Specifically, it showcases how defining structs with common initial members (akin to base classes) and using function pointers within these structs allows different "derived" structs to implement their own versions of specific operations, effectively mimicking virtual methods. This enables flexible and extensible code that can handle various data types or operations without needing to know the specific concrete type at compile time, achieving runtime polymorphism.
Memfault, a platform for monitoring and debugging connected devices, is seeking an experienced Android System (AOSP) engineer. This role involves working deeply within the Android Open Source Project to develop and improve Memfault's firmware over-the-air (FOTA) updating system and device monitoring capabilities. The ideal candidate possesses strong C/C++ skills, a deep understanding of AOSP internals, and experience with embedded systems, particularly in the realm of firmware updates and low-level debugging. This position offers the opportunity to contribute to a fast-growing startup and shape the future of device reliability.
Several commenters on Hacker News expressed interest in the Memfault position, inquiring about remote work possibilities and the specific nature of "low-level" work involved. Some discussion revolved around the challenges and rewards of working with AOSP, with one commenter highlighting the complexity and fragmentation of the Android ecosystem. Others noted the niche nature of embedded Android/AOSP development and the potential career benefits of specializing in this area. A few commenters also touched upon Memfault's business model and the value proposition of their product for embedded developers. One comment suggested exploring similar tools in the embedded Linux space, while another briefly discussed the intricacies of AOSP customization by different device manufacturers.
The author's Chumby 8, a vintage internet appliance, consistently ran at 100% CPU usage due to a kernel bug affecting the way the CPU's clock frequency was handled. The original kernel expected a constant clock speed, but the Chumby's CPU dynamically scaled its frequency. This discrepancy caused the kernel's timekeeping functions to malfunction, leading to a busy loop that consumed all available CPU cycles. Upgrading to a newer kernel, compiled with the correct configuration for a variable clock speed, resolved the issue and brought CPU usage back to normal levels.
The Hacker News comments primarily focus on the surprising complexity and challenges involved in the author's quest to upgrade the kernel of a Chumby 8. Several commenters expressed admiration for the author's deep dive into the embedded system's inner workings, with some jokingly comparing it to a software archaeological expedition. There's also discussion about the prevalence of inefficient browser implementations on embedded devices, contributing to high CPU usage. Some suggest alternative approaches, like using a lightweight browser or a different operating system entirely. A few commenters shared their own experiences with similar embedded devices and the difficulties in optimizing their performance. The overall sentiment reflects appreciation for the author's detailed troubleshooting process and the interesting technical insights it provides.
bpftune is a new open-source tool from Oracle that leverages eBPF (extended Berkeley Packet Filter) to automatically tune Linux system parameters. It dynamically adjusts settings related to networking, memory management, and other kernel subsystems based on real-time workload characteristics and system performance. The goal is to optimize performance and resource utilization without requiring manual intervention or system-specific expertise, making it easier to adapt to changing workloads and achieve optimal system behavior.
Hacker News commenters generally expressed interest in bpftune and its potential. Some questioned the overhead of constantly monitoring and tuning, while others highlighted the benefits for dynamic workloads. A few users pointed out existing tools like tuned-adm, expressing curiosity about bpftune's advantages over them. The project's novelty and use of eBPF were appreciated, with some anticipating its integration into existing performance tuning workflows. A desire for clear documentation and examples of real-world usage was also expressed. Several commenters were specifically intrigued by the network latency use case, hoping for more details and benchmarks.
Summary of Comments ( 67 )
https://news.ycombinator.com/item?id=43280517
Hacker News users generally praised the article for its clear explanation of polymorphism in C, particularly how FFmpeg and the Linux kernel utilize function pointers and structs to achieve object-oriented-like designs. Several commenters pointed out the trade-offs of this approach, highlighting the increased complexity for debugging and the potential performance overhead compared to simpler C code or using C++. One commenter shared personal experience working with FFmpeg's codebase, confirming the article's description of its design. Another noted the value in understanding these techniques even if using higher-level languages, as it helps with interacting with C libraries and understanding lower-level system design. Some discussion focused on the benefits and drawbacks of C++'s object model compared to C's approach, with some suggesting modern C++ offers a more manageable way to achieve polymorphism. A few commenters mentioned other examples of similar techniques in different C projects, broadening the context of the article.
The Hacker News post "Exploring Polymorphism in C: Lessons from Linux and FFmpeg's Code Design (2019)" has a modest number of comments, generating a brief discussion around the topic of object-oriented programming (OOP) in C. While not a large or particularly contentious debate, several commenters offer their perspectives on the merits and drawbacks of the approaches discussed in the article.
One commenter points out that leveraging function pointers for dynamic dispatch, a common technique for implementing polymorphism in C, often leads to a "bloated" vtable. They argue that this can negatively impact performance due to increased code size and indirect function calls. This commenter contrasts this approach with a "switch dispatch," where a switch statement is used to select the appropriate function based on a type identifier. They suggest that this approach can often be more efficient, especially in scenarios with a limited number of types.
Another commenter emphasizes the potential maintenance challenges associated with complex function pointer structures. They propose that, while powerful, this level of indirection can make the code harder to reason about and debug, especially for developers unfamiliar with the project's specific design choices. This echoes the general sentiment that achieving polymorphism in C can sometimes introduce complexity that might be more easily managed in languages with built-in OOP features.
Further discussion revolves around alternative approaches to polymorphism in C, with one commenter mentioning the use of tagged unions and generic programming techniques. This suggestion moves beyond the article's primary focus on function pointers, highlighting the variety of strategies available to C developers for achieving similar results. However, the commenter also acknowledges that these alternatives may introduce their own set of trade-offs in terms of performance and code readability.
Finally, there's a brief exchange about the trade-offs between code complexity and performance. One commenter suggests that the added complexity of OOP-style techniques in C can be justified by the performance benefits, particularly in scenarios where dynamic dispatch is crucial. Another commenter counters this, arguing that the performance gains are often negligible and not worth the increased difficulty in maintaining the codebase.
In summary, the comments section on Hacker News provides a concise but insightful discussion on the complexities and trade-offs involved in implementing polymorphism in C. The commenters touch upon performance considerations, code maintainability, and alternative approaches, offering a balanced perspective on the topic without delving into highly technical or lengthy debates.