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use crate::span;
use crate::Span;
use std::cell::RefCell;
use std::collections::BTreeSet;
#[allow(dead_code)]
enum Mode {
Panic,
Backtrace,
Noop,
}
const MODE: Mode = Mode::Noop;
thread_local! {
static SPANSTACK: RefCell<SpanStack> = RefCell::new(SpanStack::default());
}
#[derive(Default)]
struct SpanStack {
stack: Vec<Span>,
guards: BTreeSet<usize>,
}
impl SpanStack {
fn push_span(&mut self, span: Span) -> usize {
let index = self.stack.len();
self.guards.insert(index);
self.stack.push(span);
index
}
fn live_length(&self) -> usize {
self.guards.iter().next_back().map(|i| i + 1).unwrap_or(0)
}
fn prune(&mut self, index: usize) {
self.guards.remove(&index);
let new_len = self.live_length();
while self.stack.len() > new_len {
self.stack.pop();
}
}
fn top(&mut self) -> Option<&mut Span> {
self.stack.last_mut()
}
fn is_empty(&self) -> bool {
self.stack.is_empty()
}
#[allow(dead_code)]
fn len(&self) -> usize {
self.stack.len()
}
}
pub struct SpanStackGuard {
index: usize,
}
impl SpanStackGuard {
pub fn new(span: Span) -> Self {
let index = SPANSTACK.with(|stack| {
let mut stack = stack.borrow_mut();
let index = stack.push_span(span);
index
});
Self { index }
}
}
impl Drop for SpanStackGuard {
fn drop(&mut self) {
SPANSTACK.with(|stack| stack.borrow_mut().prune(self.index));
}
}
fn handle_empty_stack(msg: &'static str) {
match MODE {
Mode::Panic => panic!(msg),
Mode::Backtrace => {
warn!("{}, backtrace:\n{:?}", msg, backtrace::Backtrace::new());
}
Mode::Noop => (),
};
}
pub fn push_span(span: Span) -> SpanStackGuard {
SpanStackGuard::new(span)
}
pub fn push_span_with<F: FnOnce(&mut Span) -> Span>(f: F) -> Option<SpanStackGuard> {
let maybe_guard = SPANSTACK
.with(|stack| stack.borrow_mut().top().map(f))
.map(SpanStackGuard::new);
if maybe_guard.is_none() {
handle_empty_stack("Using push_span_with but the span stack is empty! Using noop span.");
}
maybe_guard
}
pub fn with_top<A, F: FnOnce(&mut Span) -> A>(f: F) -> Option<A> {
SPANSTACK.with(|stack| stack.borrow_mut().top().map(f))
}
pub fn with_top_or_null<A, F: FnOnce(&mut Span) -> A>(f: F) -> A {
SPANSTACK.with(|stack| match stack.borrow_mut().top() {
Some(top) => f(top),
None => {
handle_empty_stack("Using with_top but the span stack is empty! Using noop span.");
f(&mut Span::noop())
}
})
}
pub fn top_follower<S: Into<std::borrow::Cow<'static, str>>>(name: S) -> Span {
SPANSTACK.with(|stack| {
stack
.borrow_mut()
.top()
.map(|s| s.follower(name))
.unwrap_or_else(|| {
handle_empty_stack("Using with_top but the span stack is empty! Using noop span.");
span::NOOP_SPAN.follower("noop")
})
})
}
pub fn is_empty() -> bool {
SPANSTACK.with(|stack| stack.borrow().is_empty())
}
#[cfg(test)]
mod tests {
use super::*;
use crate::Span;
fn with_stack<A, F: FnOnce(&mut SpanStack) -> A>(f: F) -> A {
SPANSTACK.with(|s| f(&mut s.borrow_mut()))
}
#[test]
fn test_push() {
with_stack(|stack| assert_eq!(stack.len(), 0));
{
let _g0 = push_span(Span::noop());
with_stack(|stack| assert_eq!(stack.len(), 1));
{
let _g1 = push_span_with(|s| s.child("1"));
with_stack(|stack| assert_eq!(stack.len(), 2));
{
let _g2 = push_span_with(|s| s.child("2"));
with_stack(|stack| assert_eq!(stack.len(), 3));
}
with_stack(|stack| assert_eq!(stack.len(), 2));
}
with_stack(|stack| assert_eq!(stack.len(), 1));
}
with_stack(|stack| assert_eq!(stack.len(), 0));
}
#[test]
fn test_weird_drops() {
with_stack(|stack| assert_eq!(stack.len(), 0));
{
let _g0 = push_span(Span::noop());
with_stack(|stack| assert_eq!(stack.len(), 1));
{
let _g1 = push_span_with(|s| s.child("1"));
with_stack(|stack| assert_eq!(stack.len(), 2));
{
let _g2 = push_span_with(|s| s.child("2"));
with_stack(|stack| assert_eq!(stack.len(), 3));
{
let _g3 = push_span_with(|s| s.child("3"));
with_stack(|stack| assert_eq!(stack.len(), 4));
drop(_g0);
with_stack(|stack| assert_eq!(stack.len(), 4));
drop(_g2);
with_stack(|stack| assert_eq!(stack.len(), 4));
}
}
with_stack(|stack| assert_eq!(stack.len(), 2));
}
with_stack(|stack| assert_eq!(stack.len(), 0));
}
with_stack(|stack| assert_eq!(stack.len(), 0));
}
}