Function timer

Macro that allows to time a function and emit a histogram metric using metrics crate.

Note: with the use of another attribut macro, declaration order might matter. Especially using async-trait, depending on which one is first, you time the actual execution of the function if time macro is declared before, or the creation of the future if it's declared after.

Example

```rust use std::error::Error; use metricsexporterprometheus::PrometheusBuilder; use function_timer::time;

struct Test {}

impl Test { #[time("mymetric")] pub fn implfunction(&self) { println!("This another test"); }

#[time("another_metric")]
pub fn impl_fail_function(&self, text:&str) -> Result<(), Box<dyn Error>>{
    let number:usize = text.parse()?;
    println!("{number}");

    Ok(())
}

#[time("my_metric")]
pub fn static_function() {
    println!("This another test");
}

}

[time("my_metric")]

pub fn free_function() { println!("This a test"); }

fn main() -> Result<(), Box> { let builder = PrometheusBuilder::new(); let handle = builder.install_recorder()?;

free_function();

Test::static_function();

let t = Test {};
t.impl_function();

let result = t.impl_fail_function("azerty");
assert!(result.is_err());
let result = t.impl_fail_function("1");
assert!(result.is_ok());


println!("{}", handle.render());

Ok(())

} ```

Output : ``` This a test This another test This another test 1

TYPE another_metric summary

anothermetric{function="implfailfunction",quantile="0"} 0.000000677 anothermetric{function="implfailfunction",quantile="0.5"} 0.0000006770639874327633 anothermetric{function="implfailfunction",quantile="0.9"} 0.0000006770639874327633 anothermetric{function="implfailfunction",quantile="0.95"} 0.0000006770639874327633 anothermetric{function="implfailfunction",quantile="0.99"} 0.0000006770639874327633 anothermetric{function="implfailfunction",quantile="0.999"} 0.0000006770639874327633 anothermetric{function="implfailfunction",quantile="1"} 0.000012062 anothermetricsum{function="implfailfunction"} 0.000012739000000000001 anothermetriccount{function="implfail_function"} 2

TYPE my_metric summary

mymetric{function="freefunction",quantile="0"} 0.000005702 mymetric{function="freefunction",quantile="0.5"} 0.000005701963063845405 mymetric{function="freefunction",quantile="0.9"} 0.000005701963063845405 mymetric{function="freefunction",quantile="0.95"} 0.000005701963063845405 mymetric{function="freefunction",quantile="0.99"} 0.000005701963063845405 mymetric{function="freefunction",quantile="0.999"} 0.000005701963063845405 mymetric{function="freefunction",quantile="1"} 0.000005702 mymetricsum{function="freefunction"} 0.000005702 mymetriccount{function="freefunction"} 1 mymetric{function="implfunction",quantile="0"} 0.000002602 mymetric{function="implfunction",quantile="0.5"} 0.0000026018182046361393 mymetric{function="implfunction",quantile="0.9"} 0.0000026018182046361393 mymetric{function="implfunction",quantile="0.95"} 0.0000026018182046361393 mymetric{function="implfunction",quantile="0.99"} 0.0000026018182046361393 mymetric{function="implfunction",quantile="0.999"} 0.0000026018182046361393 mymetric{function="implfunction",quantile="1"} 0.000002602 mymetricsum{function="implfunction"} 0.000002602 mymetriccount{function="implfunction"} 1 mymetric{function="staticfunction",quantile="0"} 0.000002894 mymetric{function="staticfunction",quantile="0.5"} 0.0000028939157344447597 mymetric{function="staticfunction",quantile="0.9"} 0.0000028939157344447597 mymetric{function="staticfunction",quantile="0.95"} 0.0000028939157344447597 mymetric{function="staticfunction",quantile="0.99"} 0.0000028939157344447597 mymetric{function="staticfunction",quantile="0.999"} 0.0000028939157344447597 mymetric{function="staticfunction",quantile="1"} 0.000002894 mymetricsum{function="staticfunction"} 0.000002894 mymetriccount{function="staticfunction"} 1 ```

It can also be put on an impl block :

```rust use std::error::Error; use metricsexporterprometheus::PrometheusBuilder; use function_timer::time;

struct Test {}

[time("my_metric")]

impl Test { pub fn impl_function(&self) { println!("This another test"); }

pub fn impl_fail_function(&self, text:&str) -> Result<(), Box<dyn Error>>{
    let number:usize = text.parse()?;
    println!("{number}");

    Ok(())
}

pub fn static_function() {
    println!("This another test");
}

}

fn main() -> Result<(), Box> { let builder = PrometheusBuilder::new(); let handle = builder.install_recorder()?;

Test::static_function();

let t = Test {};
t.impl_function();

let result = t.impl_fail_function("azerty");
assert!(result.is_err());
let result = t.impl_fail_function("1");
assert!(result.is_ok());


println!("{}", handle.render());

Ok(())

} ```

It will output :

``` This another test This another test 1

TYPE my_metric summary

mymetric{struct="Test",function="staticfunction",quantile="0"} 0.000005976 mymetric{struct="Test",function="staticfunction",quantile="0.5"} 0.000005976352983111928 mymetric{struct="Test",function="staticfunction",quantile="0.9"} 0.000005976352983111928 mymetric{struct="Test",function="staticfunction",quantile="0.95"} 0.000005976352983111928 mymetric{struct="Test",function="staticfunction",quantile="0.99"} 0.000005976352983111928 mymetric{struct="Test",function="staticfunction",quantile="0.999"} 0.000005976352983111928 mymetric{struct="Test",function="staticfunction",quantile="1"} 0.000005976 mymetricsum{struct="Test",function="staticfunction"} 0.000005976 mymetriccount{struct="Test",function="staticfunction"} 1 mymetric{struct="Test",function="implfailfunction",quantile="0"} 0.000000771 mymetric{struct="Test",function="implfailfunction",quantile="0.5"} 0.0000007710596865495025 mymetric{struct="Test",function="implfailfunction",quantile="0.9"} 0.0000007710596865495025 mymetric{struct="Test",function="implfailfunction",quantile="0.95"} 0.0000007710596865495025 mymetric{struct="Test",function="implfailfunction",quantile="0.99"} 0.0000007710596865495025 mymetric{struct="Test",function="implfailfunction",quantile="0.999"} 0.0000007710596865495025 mymetric{struct="Test",function="implfailfunction",quantile="1"} 0.00000257 mymetricsum{struct="Test",function="implfailfunction"} 0.000003341 mymetriccount{struct="Test",function="implfailfunction"} 2 mymetric{struct="Test",function="implfunction",quantile="0"} 0.000003853 mymetric{struct="Test",function="implfunction",quantile="0.5"} 0.000003852839894857494 mymetric{struct="Test",function="implfunction",quantile="0.9"} 0.000003852839894857494 mymetric{struct="Test",function="implfunction",quantile="0.95"} 0.000003852839894857494 mymetric{struct="Test",function="implfunction",quantile="0.99"} 0.000003852839894857494 mymetric{struct="Test",function="implfunction",quantile="0.999"} 0.000003852839894857494 mymetric{struct="Test",function="implfunction",quantile="1"} 0.000003853 mymetricsum{struct="Test",function="implfunction"} 0.000003853 mymetriccount{struct="Test",function="impl_function"} 1 ```