Optimize named params via caching and use of smallvec

src/util/mod.rs

@@ -0,0 +1,5 @@
+// Internal utilities
+pub(crate) mod param_cache;
+mod small_cstr;
+pub(crate) use param_cache::ParamIndexCache;
+pub(crate) use small_cstr::SmallCString;

src/util/param_cache.rs

@@ -0,0 +1,60 @@
+use super::SmallCString;
+use std::cell::RefCell;
+use std::collections::BTreeMap;
+
+/// Maps parameter names to parameter indices.
+#[derive(Default, Clone, Debug)]
+// BTreeMap seems to do better here unless we want to pull in a custom hash
+// function.
+pub(crate) struct ParamIndexCache(RefCell<BTreeMap<SmallCString, usize>>);
+
+impl ParamIndexCache {
+    pub fn get_or_insert_with<F>(&self, s: &str, func: F) -> Option<usize>
+    where
+        F: FnOnce(&std::ffi::CStr) -> Option<usize>,
+    {
+        let mut cache = self.0.borrow_mut();
+        // Avoid entry API, needs allocation to test membership.
+        if let Some(v) = cache.get(s) {
+            return Some(*v);
+        }
+        // If there's an internal nul in the name it couldn't have been a
+        // parameter, so early return here is ok.
+        let name = SmallCString::new(s).ok()?;
+        let val = func(&name)?;
+        cache.insert(name, val);
+        Some(val)
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    #[test]
+    fn test_cache() {
+        let p = ParamIndexCache::default();
+        let v = p.get_or_insert_with("foo", |cstr| {
+            assert_eq!(cstr.to_str().unwrap(), "foo");
+            Some(3)
+        });
+        assert_eq!(v, Some(3));
+        let v = p.get_or_insert_with("foo", |_| {
+            panic!("shouldn't be called this time");
+        });
+        assert_eq!(v, Some(3));
+        let v = p.get_or_insert_with("gar\0bage", |_| {
+            panic!("shouldn't be called here either");
+        });
+        assert_eq!(v, None);
+        let v = p.get_or_insert_with("bar", |cstr| {
+            assert_eq!(cstr.to_str().unwrap(), "bar");
+            None
+        });
+        assert_eq!(v, None);
+        let v = p.get_or_insert_with("bar", |cstr| {
+            assert_eq!(cstr.to_str().unwrap(), "bar");
+            Some(30)
+        });
+        assert_eq!(v, Some(30));
+    }
+}

src/util/small_cstr.rs

@@ -0,0 +1,132 @@
+use smallvec::{smallvec, SmallVec};
+use std::ffi::{CStr, CString, NulError};
+
+#[derive(Clone, PartialEq, Eq, PartialOrd, Ord)]
+pub struct SmallCString(smallvec::SmallVec<[u8; 16]>);
+
+impl SmallCString {
+    #[inline]
+    pub fn new(s: &str) -> Result<Self, NulError> {
+        if s.as_bytes().contains(&0u8) {
+            return Err(Self::fabricate_nul_error(s));
+        }
+        let mut buf = SmallVec::with_capacity(s.len() + 1);
+        buf.extend_from_slice(s.as_bytes());
+        buf.push(0);
+        Ok(Self(buf))
+    }
+
+    #[inline]
+    pub fn as_str(&self) -> &str {
+        debug_assert!(std::str::from_utf8(&self.as_bytes_without_nul()).is_ok());
+        // Constructor takes a &str so this is safe.
+        unsafe { std::str::from_utf8_unchecked(&self.as_bytes_without_nul()) }
+    }
+
+    #[inline]
+    pub fn as_bytes_without_nul(&self) -> &[u8] {
+        &self.0[..self.0.len() - 1]
+    }
+
+    #[inline]
+    pub fn len(&self) -> usize {
+        debug_assert_ne!(self.0.len(), 0);
+        self.0.len() - 1
+    }
+
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    #[inline]
+    pub fn as_cstr(&self) -> &CStr {
+        debug_assert!(CStr::from_bytes_with_nul(&self.0).is_ok());
+        unsafe { CStr::from_bytes_with_nul_unchecked(&self.0) }
+    }
+
+    #[cold]
+    fn fabricate_nul_error(b: &str) -> NulError {
+        CString::new(b).unwrap_err()
+    }
+}
+
+impl Default for SmallCString {
+    #[inline]
+    fn default() -> Self {
+        Self(smallvec![0])
+    }
+}
+
+impl std::fmt::Debug for SmallCString {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_tuple("SmallCString").field(&self.as_str()).finish()
+    }
+}
+
+impl std::ops::Deref for SmallCString {
+    type Target = CStr;
+    #[inline]
+    fn deref(&self) -> &CStr {
+        self.as_cstr()
+    }
+}
+
+impl PartialEq<SmallCString> for str {
+    #[inline]
+    fn eq(&self, s: &SmallCString) -> bool {
+        s.as_bytes_without_nul() == self.as_bytes()
+    }
+}
+
+impl PartialEq<str> for SmallCString {
+    #[inline]
+    fn eq(&self, s: &str) -> bool {
+        self.as_bytes_without_nul() == s.as_bytes()
+    }
+}
+
+impl std::borrow::Borrow<str> for SmallCString {
+    #[inline]
+    fn borrow(&self) -> &str {
+        self.as_str()
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_small_cstring() {
+        // We don't go through the normal machinery for default, so make sure
+        // things work.
+        assert_eq!(SmallCString::default().0, SmallCString::new("").unwrap().0);
+        assert_eq!(SmallCString::new("foo").unwrap().len(), 3);
+        assert_eq!(SmallCString::new("foo").unwrap().0.as_slice(), b"foo\0");
+        assert_eq!(
+            SmallCString::new("foo").unwrap().as_bytes_without_nul(),
+            b"foo",
+        );
+
+        assert_eq!(SmallCString::new("😀").unwrap().len(), 4);
+        assert_eq!(
+            SmallCString::new("😀").unwrap().0.as_slice(),
+            b"\xf0\x9f\x98\x80\0",
+        );
+        assert_eq!(
+            SmallCString::new("😀").unwrap().as_bytes_without_nul(),
+            b"\xf0\x9f\x98\x80",
+        );
+
+        assert_eq!(SmallCString::new("").unwrap().len(), 0);
+        assert!(SmallCString::new("").unwrap().is_empty());
+
+        assert_eq!(SmallCString::new("").unwrap().0.as_slice(), b"\0");
+        assert_eq!(SmallCString::new("").unwrap().as_bytes_without_nul(), b"");
+
+        assert!(SmallCString::new("\0").is_err());
+        assert!(SmallCString::new("\0abc").is_err());
+        assert!(SmallCString::new("abc\0").is_err());
+    }
+}