nushell/crates/nu-command/src/bytes/length.rs
Stefan Holderbach a52386e837
Box ShellError in Value::Error (#8375)
# Description

Our `ShellError` at the moment has a `std::mem::size_of<ShellError>` of
136 bytes (on AMD64). As a result `Value` directly storing the struct
also required 136 bytes (thanks to alignment requirements).

This change stores the `Value::Error` `ShellError` on the heap.

Pro:
- Value now needs just 80 bytes
- Should be 1 cacheline less (still at least 2 cachelines)

Con:
- More small heap allocations when dealing with `Value::Error`
  - More heap fragmentation
  - Potential for additional required memcopies

# Further code changes

Includes a small refactor of `try` due to a type mismatch in its large
match.

# User-Facing Changes

None for regular users.

Plugin authors may have to update their matches on `Value` if they use
`nu-protocol`

Needs benchmarking to see if there is a benefit in real world workloads.
**Update** small improvements in runtime for workloads with high volume
of values. Significant reduction in maximum resident set size, when many
values are held in memory.

# Tests + Formatting
2023-03-12 09:57:27 +01:00

98 lines
2.8 KiB
Rust

use crate::input_handler::{operate, CellPathOnlyArgs};
use nu_engine::CallExt;
use nu_protocol::ast::Call;
use nu_protocol::ast::CellPath;
use nu_protocol::engine::{Command, EngineState, Stack};
use nu_protocol::Category;
use nu_protocol::{Example, PipelineData, ShellError, Signature, Span, SyntaxShape, Type, Value};
#[derive(Clone)]
pub struct BytesLen;
impl Command for BytesLen {
fn name(&self) -> &str {
"bytes length"
}
fn signature(&self) -> Signature {
Signature::build("bytes length")
.input_output_types(vec![(Type::Binary, Type::Int)])
.vectorizes_over_list(true)
.rest(
"rest",
SyntaxShape::CellPath,
"for a data structure input, find the length of data at the given cell paths",
)
.category(Category::Bytes)
}
fn usage(&self) -> &str {
"Output the length of any bytes in the pipeline."
}
fn search_terms(&self) -> Vec<&str> {
vec!["size", "count"]
}
fn run(
&self,
engine_state: &EngineState,
stack: &mut Stack,
call: &Call,
input: PipelineData,
) -> Result<PipelineData, ShellError> {
let cell_paths: Vec<CellPath> = call.rest(engine_state, stack, 1)?;
let arg = CellPathOnlyArgs::from(cell_paths);
operate(length, arg, input, call.head, engine_state.ctrlc.clone())
}
fn examples(&self) -> Vec<Example> {
vec![
Example {
description: "Return the lengths of multiple strings",
example: "0x[1F FF AA AB] | bytes length",
result: Some(Value::test_int(4)),
},
Example {
description: "Return the lengths of multiple strings",
example: "[0x[1F FF AA AB] 0x[1F]] | bytes length",
result: Some(Value::List {
vals: vec![Value::test_int(4), Value::test_int(1)],
span: Span::test_data(),
}),
},
]
}
}
fn length(val: &Value, _args: &CellPathOnlyArgs, span: Span) -> Value {
match val {
Value::Binary {
val,
span: val_span,
} => Value::int(val.len() as i64, *val_span),
// Propagate errors by explicitly matching them before the final case.
Value::Error { .. } => val.clone(),
other => Value::Error {
error: Box::new(ShellError::OnlySupportsThisInputType {
exp_input_type: "binary".into(),
wrong_type: other.get_type().to_string(),
dst_span: span,
src_span: other.expect_span(),
}),
},
}
}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn test_examples() {
use crate::test_examples;
test_examples(BytesLen {})
}
}