# mem_dbg [![downloads](https://img.shields.io/crates/d/mem_dbg)](https://crates.io/crates/mem_dbg) [![dependents](https://img.shields.io/librariesio/dependents/cargo/mem_dbg)](https://crates.io/crates/mem_dbg/reverse_dependencies) ![GitHub CI](https://github.com/zommiommy/mem_dbg-rs/actions/workflows/rust.yml/badge.svg) ![license](https://img.shields.io/crates/l/mem_dbg) [![](https://tokei.rs/b1/github/zommiommy/mem_dbg-rs?type=Rust,Python)](https://github.com/zommiommy/mem_dbg-rs) [![Latest version](https://img.shields.io/crates/v/mem_dbg.svg)](https://crates.io/crates/mem_dbg) [![Documentation](https://docs.rs/mem_dbg/badge.svg)](https://docs.rs/mem_dbg) Traits and associated procedural macros to display recursively the layout and memory usage of a value. The trait [`MemDbg`] can be used to display the recursive layout of a value, together with the size of each part and the associated padding bytes. We provide implementations for most basic types, a derive macro for structs and enums whose fields implement [`MemDbg`], and support for a few other crates. To compute the size, we provide the trait [`MemSize`] and a derive macro that can be used to compute the size of a value in bytes as the standard library function [`std::mem::size_of`] returns the stack size of a type in bytes, but it does not take into consideration heap memory. ## Why `MemSize` Other traits partially provide the functionality of [`MemSize`], but either they require implementing manually a trait, which is prone to error, or they do not provide the flexibility necessary for [`MemDbg`]. Most importantly, [`MemSize`] uses the type system to avoid iterating over the content of a container (a vector, etc.) when it is not necessary, making it possible to compute instantly the size of values occupying hundreds of gigabytes of heap memory. This is the result of the benchmark `bench_hash_map` contained in the `examples` directory. It builds a hash map with a hundred million entries and then measures its heap size: ```test Allocated: 2281701509 get_size: 1879048240 152477833 ns deep_size_of: 1879048240 152482000 ns size_of: 2281701432 152261958 ns mem_size: 2281701424 209 ns ``` The first line is the number of bytes allocated by the program as returned by [`cap`]. Then, we display the result of [`get-size`], [`deepsize`], [`size-of`], and our own [`MemSize`]. Note that the first two crates are just measuring the space used by the items, and not by the data structure (i.e., they are not taking into account the load factor and the power-of-two size constraint of the hash map). Moreover, all other crates are about six orders of magnitude slower than our implementation, due to the necessity to iterate over all elements. ## Padding The trait [`MemDbg`] is useful to display the layout of a value and understand how much memory is used by each part. In particular, it exploits the new stable macro [`std::mem::offset_of`] to display the padding of each field in square brackets; moreover, the flag [`DbgFlags::RUST_LAYOUT`] makes it possible to display structures in the layout used by the Rust compiler, rather than that given by declaration order. These features are also available for enums using the feature `offset_of_enum`, which however needs the nightly compiler, as it enables the unstable features `offset_of_enum` and `offset_of_nested`. ## Features - `offset_of_enum`: support for padding and for the `DbgFlags::RUST_LAYOUT` flag for enums. Requires the nightly compiler as it enables the unstable features `offset_of_enum` and `offset_of_nested`. Calling `mem_dbg` with the flag `DbgFlags::RUST_LAYOUT` without this feature enabled will result in a panic. - `half`: support for the [`half`] crate. - `maligned`: support for the [`maligned`] crate. - `mmap-rs`: support for the [`mmap-rs`] crate. - `rand`: support for the [`rand`] crate. ## Example ```rust # #![cfg_attr(feature = "offset_of_enum", feature(offset_of_enum, offset_of_nested))] # fn main() -> Result<(), Box> { use mem_dbg::*; #[derive(MemSize, MemDbg)] struct Struct { a: A, b: B, test: isize, } #[derive(MemSize, MemDbg)] struct Data { a: A, b: Vec, c: (u8, String), } #[derive(MemSize, MemDbg)] enum TestEnum { Unit, Unit2(), Unit3 {}, Unnamed(usize, u8), Named { first: usize, second: u8 }, } let b = Vec::with_capacity(100); let s = Struct { a: TestEnum::Unnamed(0, 16), b: Data { a: vec![0x42_u8; 700], b, c: (1, "foo".to_owned()), }, test: -0xbadf00d, }; println!("size: {}", s.mem_size(SizeFlags::default())); println!("capacity: {}", s.mem_size(SizeFlags::CAPACITY)); println!(); s.mem_dbg(DbgFlags::empty())?; println!(); println!("size: {}", s.mem_size(SizeFlags::default())); println!("capacity: {}", s.mem_size(SizeFlags::CAPACITY)); println!(); s.mem_dbg(DbgFlags::default() | DbgFlags::CAPACITY | DbgFlags::HUMANIZE)?; #[cfg(feature = "offset_of_enum")] { println!(); println!("size: {}", s.mem_size(SizeFlags::default())); println!("capacity: {}", s.mem_size(SizeFlags::CAPACITY)); println!(); s.mem_dbg(DbgFlags::empty() | DbgFlags::RUST_LAYOUT)?; } # Ok(()) # } ``` The previous program prints: ```test size: 807 capacity: 1207 807 B ⏺ 16 B ├╴a │ ├╴Variant: Unnamed 8 B │ ├╴0 1 B │ ╰╴1 783 B ├╴b 724 B │ ├╴a 24 B │ ├╴b 35 B │ ╰╴c 1 B │ ├╴0 [7B] 27 B │ ╰╴1 8 B ╰╴test size: 807 capacity: 1207 1.207 kB 100.00% ⏺: readme::main::Struct>> 16 B 1.33% ├╴a: readme::main::TestEnum │ ├╴Variant: Unnamed 8 B 0.66% │ ├╴0: usize 1 B 0.08% │ ╰╴1: u8 1.183 kB 98.01% ├╴b: readme::main::Data> 724 B 59.98% │ ├╴a: alloc::vec::Vec 424 B 35.13% │ ├╴b: alloc::vec::Vec 35 B 2.90% │ ╰╴c: (u8, alloc::string::String) 1 B 0.08% │ ├╴0: u8 [7B] 27 B 2.24% │ ╰╴1: alloc::string::String 8 B 0.66% ╰╴test: isize ``` If run with the feature `offset_of_enum`, it prints: ```text size: 807 capacity: 1207 807 B ⏺ 16 B ├╴a │ ├╴Variant: Unnamed 8 B │ ├╴0 1 B │ ╰╴1 [6B] 783 B ├╴b 724 B │ ├╴a 24 B │ ├╴b 35 B │ ╰╴c 1 B │ ├╴0 [7B] 27 B │ ╰╴1 8 B ╰╴test size: 807 capacity: 1207 1.207 kB 100.00% ⏺: readme::main::Struct>> 16 B 1.33% ├╴a: readme::main::TestEnum │ ├╴Variant: Unnamed 8 B 0.66% │ ├╴0: usize 1 B 0.08% │ ╰╴1: u8 [6B] 1.183 kB 98.01% ├╴b: readme::main::Data> 724 B 59.98% │ ├╴a: alloc::vec::Vec 424 B 35.13% │ ├╴b: alloc::vec::Vec 35 B 2.90% │ ╰╴c: (u8, alloc::string::String) 1 B 0.08% │ ├╴0: u8 [7B] 27 B 2.24% │ ╰╴1: alloc::string::String 8 B 0.66% ╰╴test: isize size: 807 capacity: 1207 807 B ⏺ 783 B ├╴b 724 B │ ├╴a 24 B │ ├╴b 35 B │ ╰╴c 1 B │ ├╴0 [7B] 27 B │ ╰╴1 16 B ├╴a │ ├╴Variant: Unnamed 1 B │ ├╴1 [6B] 8 B │ ╰╴0 8 B ╰╴test ``` ## Caveats - We support out-of-the-box most basic types, and tuples up to size ten. The derive macros `MemSize`/`MemDbg` will generate implementations for structs and enums whose fields implement the associated interface: if this is not the case (e.g., because of the orphan rule) one can implement the traits manually. - If you invoke the methods of this crate on a shared reference, the compiler will automatically dereference it, and the method will be invoked on the referenced type: ```rust # fn main() -> Result<(), Box> { use mem_dbg::*; let mut x: [i32; 4] = [0, 0, 0, 0]; assert_eq!( (&x).mem_size(SizeFlags::default()), std::mem::size_of::<[i32; 4]>() ); assert_eq!( (&mut x).mem_size(SizeFlags::default()), std::mem::size_of::<&mut [i32; 4]>() ); assert_eq!( <&[i32; 4] as MemSize>::mem_size(&&x, SizeFlags::default()), std::mem::size_of::<&[i32; 4]>() ); # Ok(()) # } ``` - Computation of the size of arrays, slices, and vectors will be performed by iterating over their elements unless the type is a copy type that does not contain non-`'static` references and it is declared as such using the attribute `#[copy_type]`. See [`CopyType`] for more details. - The content of vectors and slices is not expanded recursively as the output might be too complex; this might change in the future (e.g., via a flag) should interesting use cases arise. - `BTreeMap`/`BTreeSet` are not currently supported as we still have to figure out a way to precisely measure their memory size and capacity. [`MemDbg`]: [`MemSize`]: [`std::mem::size_of`]: [`DbgFlags::RUST_LAYOUT`]: [`CopyType`]: [`cap`]: [`get-size`]: [`deepsize`]: [`size-of`]: [`maligned`]: [`mmap-rs`]: [`half`]: [`rand`]: