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

104 lines
2.8 KiB
Rust

use nu_engine::CallExt;
use nu_protocol::ast::Call;
use nu_protocol::engine::{Command, EngineState, Stack};
use nu_protocol::{
Category, Example, PipelineData, ShellError, Signature, Span, SyntaxShape, Type, Value,
};
#[derive(Clone)]
pub struct SubCommand;
impl Command for SubCommand {
fn name(&self) -> &str {
"bits xor"
}
fn signature(&self) -> Signature {
Signature::build("bits xor")
.input_output_types(vec![(Type::Int, Type::Int)])
.vectorizes_over_list(true)
.required(
"target",
SyntaxShape::Int,
"target integer to perform bit xor",
)
.category(Category::Bits)
}
fn usage(&self) -> &str {
"Performs bitwise xor for integers."
}
fn search_terms(&self) -> Vec<&str> {
vec!["logic xor"]
}
fn run(
&self,
engine_state: &EngineState,
stack: &mut Stack,
call: &Call,
input: PipelineData,
) -> Result<PipelineData, ShellError> {
let head = call.head;
let target: i64 = call.req(engine_state, stack, 0)?;
// This doesn't match explicit nulls
if matches!(input, PipelineData::Empty) {
return Err(ShellError::PipelineEmpty { dst_span: head });
}
input.map(
move |value| operate(value, target, head),
engine_state.ctrlc.clone(),
)
}
fn examples(&self) -> Vec<Example> {
vec![
Example {
description: "Apply bits xor to two numbers",
example: "2 | bits xor 2",
result: Some(Value::test_int(0)),
},
Example {
description: "Apply logical xor to a list of numbers",
example: "[8 3 2] | bits xor 2",
result: Some(Value::List {
vals: vec![Value::test_int(10), Value::test_int(1), Value::test_int(0)],
span: Span::test_data(),
}),
},
]
}
}
fn operate(value: Value, target: i64, head: Span) -> Value {
match value {
Value::Int { val, span } => Value::Int {
val: val ^ target,
span,
},
// Propagate errors by explicitly matching them before the final case.
Value::Error { .. } => value,
other => Value::Error {
error: Box::new(ShellError::OnlySupportsThisInputType {
exp_input_type: "integer".into(),
wrong_type: other.get_type().to_string(),
dst_span: head,
src_span: other.expect_span(),
}),
},
}
}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn test_examples() {
use crate::test_examples;
test_examples(SubCommand {})
}
}