7/1/2023 0 Comments Memory mapped file![]() ![]() mio, on the other hand, manages this internally, accepting any offset and finding the nearest page boundary.Īlbeit a minor nitpick, Boost.Iostreams implements memory mapped file IO with a std::shared_ptr to provide shared semantics, even if not needed, and the overhead of the heap allocation may be unnecessary and/or unwanted. This is possible with mio.įurthermore, Boost.Iostreams' solution requires that the user pick offsets exactly at page boundaries, which is cumbersome and error prone. More seriously, the primary motivation for writing this library instead of using Boost.Iostreams, was the lack of support for establishing a memory mapping with an already open file handle/descriptor. Why?īecause memory mapping is the best thing since sliced bread! Please feel free to open an issue, I'll try to address any concerns as best I can. no dependencies) in any C++ project that needs memory mapped file IO without the need to pull in Boost. Mio has been created with the goal to be easily includable (i.e. ![]() If your software is unsound in the face of concurrent edits to some file, then say that.An easy to use header-only cross-platform C++11 memory mapping library with an MIT license. If we were writing Cassandra in Rust, we'd give out references to parts of the SSTable, but never mutable references, and they would have lifetimes bound to a query (for example) that allowed us to eventually do things like delete an old SSTable.ĭo be sure to document your assumptions though. That's what's meant by a safe abstraction: within the reasonable bounds of your system, you ensure that the language's usual constraints apply. Much like other shared references in Rust: it's all fine as long as there are no mutable references, and the data lives long enough. So it's pretty safe to have pointers into that space. Within scope, nothing will ever edit an SSTable. An outside process with the appropriate perms could go scribble on them, sure, but that's well beyond the design envelope of the database. But they're all, within the DBMS, immutable files. It makes extensive use of memory-mapped files. We're not, generally speaking, trying to account for Byzantine failures here. It's well understood, for example, that you just don't go around editing your database's files while it's running, and expect that to work. ![]() We'll do our best to keep these links up to date, but if we fall behind please don't hesitate to shoot us a modmail. This is not an official Rust forum, and cannot fulfill feature requests. Err on the side of giving others the benefit of the doubt.Īvoid re-treading topics that have been long-settled or utterly exhausted. Please create a read-only mirror and link that instead.Ī programming language is rarely worth getting worked up over.īe charitable in intent. If criticizing a project on GitHub, you may not link directly to the project's issue tracker. Post titles should include useful context.įor Rust questions, use the stickied Q&A thread.Īrts-and-crafts posts are permitted on weekends.Ĭriticism is encouraged, though it must be constructive, useful and actionable. For content that does not, use a text post to explain its relevance. ![]() Posts must reference Rust or relate to things using Rust. We observe the Rust Project Code of Conduct. Strive to treat others with respect, patience, kindness, and empathy. Please read The Rust Community Code of Conduct The Rust Programming LanguageĪ place for all things related to the Rust programming language-an open-source systems language that emphasizes performance, reliability, and productivity. ![]()
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