sitraceprint

stack indented trace printing; a simple rust library to print messages indented to stack depth optionally preceded by the function name.

An "entry-level" tracing library that prints function flows in a simple manual approach.

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- About - Use - Trace-printing example - Manually setting the indentation - Shortcomings - Slow - Release builds - Code Clutter - Hogs stdout Or stderr - Other tracing crates

About

The aim of si_trace_print is to be a simple libaary to aid developers manually reviewing singular program runs. It is simple to use; not a framework, does not require compiler changes, no new Computer Science theories must be studied to understand how it works. It offers decent control over what is printed. It's great for anyone that wants some tracing in debug builds (though it may also be used in release builds) but does not want to take on a new "tracing framework" or make compiler adjustments.

si_trace_print is a good "entry-level" tracing library.

Use

Add si_trace_print entry to the project Cargo.toml section [dependencies].

Trace-printing example

The most common use will likely be debug-only eprintln with a preceding function name.

```rust use sitraceprint::{ den, deo, dex, defn, defx, };

fn main() { den!("hello from main"); deo!("main will be doing stuff..."); func1(3); deo!("main is done doing stuff."); dex!("goodbye from main"); }

fn func1(_var: usize) { defn!("({:?})", _var); defo!("doing even more stuff..."); defx!(); } ```

this should print to stderr

text $ cargo run →hello from main main will be doing stuff... →func1: (3) func1: doing even more stuff... ←func1: main is done doing stuff. ←goodbye from main

If built with --release then the de statements are not compiled and nothing would be printed.


An example using a variety of the available println macros. These compile into debug and release builds and print to stdout.

```rust extern crate sitraceprint; use sitraceprint::{pf1n, pf2n, pfn, pn, po, px};

fn main() { pn!("hello from main"); pfn!("hello again from main"); pf1n!("hello again from main!"); pf2n!("HELLO AGAIN FROM MAIN!!!"); po!("main will be doing stuff..."); mod1::mod2::func1(3); po!("main is done doing stuff..."); px!("goodbye from main"); }

mod mod1 { pub mod mod2 { use sitraceprint::{ pf1n, pf1o, pf1x, pf1ñ, pf2n, pf2o, pf2x, pf2ñ, pfn, pfo, pfx, pfñ, pñ, }; pub fn func1(var: usize) { pf1n!("({:?})", var); pf1o!("func1 calling func2..."); func2(var + 1); pf1x!("({:?})", var); } fn func2(var: usize) { pf2n!("({:?})", var); pf2o!("calling func3..."); func3(); pf2x!("({:?})", var); } fn func3() { pfn!(); func4(); pfo!("almost complete..."); pfx!(); } fn func4() { pñ!("func4 is a short function."); pfñ!("func4 is a short function."); pf1ñ!("func4 is a short function."); pf2ñ!("func4 is a short function."); } } } ```

should print to stdout

text →hello from main →main: hello again from main →main: hello again from main! →main: HELLO AGAIN FROM MAIN!!! main will be doing stuff... →mod2::func1: (3) mod2::func1: func1 calling func2... →mod1::mod2::func2: (4) mod1::mod2::func2: calling func3... →func3: ↔func4 is a short function. ↔func4: func4 is a short function. ↔mod2::func4: func4 is a short function. ↔mod1::mod2::func4: func4 is a short function. func3: almost complete... ←func3: ←mod1::mod2::func2: (4) ←mod2::func1: (3) main is done doing stuff... ←goodbye from main

Manually setting the indentation

The first use of a library macro will set the "original" stack depth. This is later used to calculate indentation offsets. If the first use of this library is several functions into a program then later printing may be lose indentation.

```rust use sitraceprint::{ pfo, pfn, pfx, pfñ, };

fn main() { func1(3); pfx!("goodbye from main (this is not indented!)"); }

fn func1(var: usize) { func2(var); pfñ!("({:?}) (this is not indented!)", var); }

fn func2(var: usize) { // this is the first call to a sitraceprint function // the "original" stack offset will be set from here pfn!("({:?})", var); pfo!("stackdepth {:?}, stackoffset {:?}", stackdepth(), stackoffset()); pfx!("({:?})", var); } ```

prints poorly indented output

text →func2: (3) func2: stack_depth 15, stack_offset 0 ←func2: (3) ↔func1: (3) (this is not indented!) ←main: goodbye from main (this is not indented!)

Explicitly call stack_offset_set near the beginning of the thread.

```rust use sitraceprint::{ pfo, pfn, pfx, pfñ, };

fn main() { // the "original" stack offset will be set from here stackoffsetset(None); func1(3); pfx!("goodbye from main"); }

fn func1(var: usize) { func2(var); pfñ!("stackdepth {:?}, stackoffset {:?}", stackdepth(), stackoffset()); }

fn func2(var: usize) { pfn!("({:?})", var); pfo!("stackdepth {:?}, stackoffset {:?}", stackdepth(), stackoffset()); pfx!("({:?})", var); } ```

this printed

text →func2: (3) func2: stack_depth 15, stack_offset 2 ←func2: (3) ↔func1: stack_depth 14, stack_offset 1 ←main: goodbye from main

The indentation is improved but is too far indented. The indentation amount to pass to stack_offset_set can be somewhat unpredictable. It depends on build settings and which thread is running, among other things. In this case, experimentation revealed value -1 to be best:

rust // ... fn main() { stack_offset_set(Some(-1)); // ...

this printed

text →func2: (3) func2: stack_depth 15, stack_offset 1 ←func2: (3) ↔func1: stack_depth 14, stack_offset 0 ←main: goodbye from main

Shortcomings

Slow

This trace function may significantly slow a program. It is recommended to use the debug version of provided macros.

Release builds

The calculation of function depth depends on stack frames counted by [backtrace::trace]. In --release builds or under other optimization profiles, some functions may be optimized inline. The count of stack frames may not change among function calls. This means the printed indentation will not reflect function call depth. This can be forcibly avoided by adding attribute #[inline(never)] to such functions, though [even that is not guaranteed to work].

Inline attributes do not guarantee that a function is inlined or not inlined, but in practice, #[inline(always)] will cause inlining in all but the most exceptional cases.

Code Clutter

This simple tracing helper requires explicit statements that some may find too messy.

Hogs stdout Or stderr

If your rust code requires sending messages on both stdout and stderr then si_trace_print will interfere.

Other tracing crates

Here are some other tracing crates with different features.

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