You have no need to flush the cache from your user-mode (non-kernel-mode) program. The OS (Linux, in the case of ubuntu) provides your application with a fresh virtual address space, with no “leftover stuff” from other programs. Without executing special OS system calls, your program can’t even get to memory that’s used for other applications. So from a cache perspective, your application start from a clean slate, as far as it’s concerned. There are cacheflush() system calls (syntax differs by OS), but unless you’re doing something out-of-the-ordinary for typical user-mode applications, you can just forget that the cache even exists; it’s just there to speed up your program, and the OS manages it via the CPU’s MMU, your app does not need to manage it.
You may have also heard about “memory leaks” (memory allocated to your application that your application forgets to free/delete, which is “lost forever” once your application forgets about it). If you’re writing a (potentially) long-running program, leaked memory is definitely a concern. But leaked memory is only an issue for the application that leaks it; in modern virtual-memory environments, if application A leaks memory, it doesn’t affect application B. And when application A exits, the OS clears out its virtual address space, and any leaked memory is at that point reclaimed by the system and no longer consumes any system resources whatsoever. In many cases, programmers specifically choose to NOT free/delete a memory allocation, knowing that the OS will automatically reclaim the entire amount of the memory when the application exits. There’s nothing wrong with that strategy, as long as the program doesn’t keep doing that on a repeating basis, exhausting its virtual address space.
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