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tests: generate prefilter tests lazily

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Generating all the prefilter test cases at once caused memory usage to
spike up to ~7.1 GB. This lazy implementation sees ~100 MB peak.

More specifically, this crate always OOMs in crater due to the sandbox
limits. In fact, its test suite can hit a peak memory usage of ~7.1 GB
which as far as one can tell is a comfortable 2x greater than any other
crate in the top 1,000 by downloads.

Closes #105
This commit is contained in:
Ben Kimock
2022-01-10 01:03:46 -05:00
committed by Andrew Gallant
parent 66add72007
commit c58a718b3c
1 changed files with 35 additions and 34 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/memmem/prefilter/mod.rs
+35 -34
View File
@@ -431,7 +431,7 @@ pub(crate) mod tests {
/// (Currently, we take the approach of massaging tests to be valid
/// instead of rejecting them outright.)
fn new(
seed: &PrefilterTestSeed,
seed: PrefilterTestSeed,
rare1i: usize,
rare2i: usize,
haystack_len: usize,
@@ -515,6 +515,7 @@ pub(crate) mod tests {
];
/// Data that describes a single prefilter test seed.
#[derive(Clone, Copy)]
struct PrefilterTestSeed {
first: u8,
rare1: u8,
@@ -523,47 +524,47 @@ pub(crate) mod tests {
impl PrefilterTestSeed {
/// Generate a series of prefilter tests from this seed.
fn generate(&self) -> Vec<PrefilterTest> {
let mut tests = vec![];
let mut push = |test: Option<PrefilterTest>| {
if let Some(test) = test {
tests.push(test);
}
};
fn generate(self) -> impl Iterator<Item = PrefilterTest> {
let len_start = 2;
// The loop below generates *a lot* of tests. The number of tests
// was chosen somewhat empirically to be "bearable" when running
// the test suite.
for needle_len in len_start..=40 {
// The iterator below generates *a lot* of tests. The number of
// tests was chosen somewhat empirically to be "bearable" when
// running the test suite.
//
// We use an iterator here because the collective haystacks of all
// these test cases add up to enough memory to OOM a conservative
// sandbox or a small laptop.
(len_start..=40).flat_map(move |needle_len| {
let rare_start = len_start - 1;
for rare1i in rare_start..needle_len {
for rare2i in rare1i..needle_len {
for haystack_len in needle_len..=66 {
push(PrefilterTest::new(
(rare_start..needle_len).flat_map(move |rare1i| {
(rare1i..needle_len).flat_map(move |rare2i| {
(needle_len..=66).flat_map(move |haystack_len| {
PrefilterTest::new(
self,
rare1i,
rare2i,
haystack_len,
needle_len,
None,
));
// Test all possible match scenarios for this
// needle and haystack.
for output in 0..=(haystack_len - needle_len) {
push(PrefilterTest::new(
self,
rare1i,
rare2i,
haystack_len,
needle_len,
Some(output),
));
}
}
}
}
}
tests
)
.into_iter()
.chain(
(0..=(haystack_len - needle_len)).flat_map(
move |output| {
PrefilterTest::new(
self,
rare1i,
rare2i,
haystack_len,
needle_len,
Some(output),
)
},
),
)
})
})
})
})
}
}
}