fix(node): reject non-ascii cfg keys

<!-- lance-gatekeeper-fix:v1 agent=5c80c44c083b3b8ad0da595419d468fc
generation=1 -->

## Root cause

The legacy synchronous Python table called `delete` on a shared, mutable
`lance.Dataset`. Concurrent table operations could hold a PyO3 borrow
while delete requested an exclusive borrow, producing `RuntimeError:
Already borrowed`. The current async-backed binding fixes this by
cloning its thread-safe Rust table handle before awaiting, but that
concurrency contract had no regression coverage.

## Fix

- Document why delete must clone the Rust table handle before entering
its async future.
- Add a barrier-synchronized regression test that deletes distinct rows
through one shared table from eight Python threads.
- Verify every delete commits exactly one row, every commit gets a
distinct version, and no rows remain.

## Validation

- `cargo check --quiet --features remote --tests --examples`
- `cargo fmt --all -- --check`
- `uv run --extra tests --extra dev ruff format --check
python/tests/test_table.py`
- `uv run --extra tests --extra dev ruff check
python/tests/test_table.py`
- `uv run --extra tests --extra dev pytest
python/tests/test_table.py::test_concurrent_deletes_are_thread_safe
python/tests/test_table.py::test_delete
python/tests/test_table.py::test_delete_expr
python/tests/test_table.py::test_delete_expr_async -q` (4 passed)
- Manual stress reproduction: 100 concurrent deletes on one table
completed at versions 2–101 with zero rows remaining.

Fixes #530

Co-authored-by: Gatefixer <313497061+lancedb-gatefixer[bot]@users.noreply.github.com>

nodejs/.cargo/config.toml

@@ -0,0 +1,21 @@
+# Keep Node's Linux x64 addons compatible with pre-Haswell CPUs.
+# lance-linalg dispatches hot vector kernels to newer SIMD tiers at runtime.
+[env]
+LANCEDB_NODE_ENFORCE_X86_64_V2 = "1"
+
+[target.x86_64-unknown-linux-gnu]
+rustflags = [
+    "-C",
+    "target-cpu=x86-64-v2",
+    "-C",
+    "target-feature=-avx,-avx2,-fma,-f16c",
+]
+
+# Preserve the workspace's dynamic C runtime configuration for musl.
+[target.x86_64-unknown-linux-musl]
+rustflags = [
+    "-C",
+    "target-cpu=x86-64-v2",
+    "-C",
+    "target-feature=-crt-static,-avx,-avx2,-fma,-f16c",
+]

nodejs/Cargo.toml

@@ -12,6 +12,10 @@ categories.workspace = true
 [lib]
 crate-type = ["cdylib"]
 
+[[test]]
+name = "x86_64_v2_build_flags"
+path = "build_support/x86_64_v2.rs"
+
 [dependencies]
 async-trait.workspace = true
 arrow-ipc.workspace = true

nodejs/__test__/cpu_compatibility.test.ts

@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-FileCopyrightText: Copyright The LanceDB Authors
+
+import * as tmp from "tmp";
+
+import { connect } from "../lancedb";
+import {
+  Field,
+  FixedSizeList,
+  Float32,
+  Int32,
+  Schema,
+  makeArrowTable,
+} from "../lancedb/arrow";
+
+test("cosine vector search runs on the pre-Haswell build baseline", async () => {
+  const tmpDir = tmp.dirSync({ unsafeCleanup: true });
+
+  try {
+    const db = await connect(tmpDir.name);
+    const schema = new Schema([
+      new Field("id", new Int32(), false),
+      new Field(
+        "vector",
+        new FixedSizeList(3, new Field("item", new Float32(), false)),
+        false,
+      ),
+    ]);
+    const data = makeArrowTable(
+      [
+        { id: 1, vector: [1, 0, 0] },
+        { id: 2, vector: [0, 1, 0] },
+      ],
+      { schema },
+    );
+    const table = await db.createTable("vectors", data);
+
+    const results = await table
+      .vectorSearch([1, 0, 0])
+      .distanceType("cosine")
+      .limit(1)
+      .toArray();
+
+    expect(results).toHaveLength(1);
+    expect(results[0].id).toBe(1);
+    expect(results[0]._distance).toBeCloseTo(0);
+  } finally {
+    tmpDir.removeCallback();
+  }
+}, 60_000);

nodejs/build.rs

@@ -3,6 +3,29 @@
 
 extern crate napi_build;
 
+use std::env;
+
+#[path = "build_support/x86_64_v2.rs"]
+mod x86_64_v2;
+
+const ENFORCE_BASELINE: &str = "LANCEDB_NODE_ENFORCE_X86_64_V2";
+
 fn main() {
     napi_build::setup();
+    println!("cargo:rerun-if-env-changed={ENFORCE_BASELINE}");
+    println!("cargo:rerun-if-env-changed=CARGO_ENCODED_RUSTFLAGS");
+
+    let is_linux_x64 = env::var("CARGO_CFG_TARGET_ARCH").as_deref() == Ok("x86_64")
+        && env::var("CARGO_CFG_TARGET_OS").as_deref() == Ok("linux");
+    let is_release = env::var("PROFILE").as_deref() == Ok("release");
+    let is_node_build = env::var(ENFORCE_BASELINE).as_deref() == Ok("1");
+
+    if !is_linux_x64 || (!is_release && !is_node_build) {
+        return;
+    }
+
+    let encoded_rustflags = env::var("CARGO_ENCODED_RUSTFLAGS").unwrap_or_default();
+    x86_64_v2::validate_encoded_rustflags(&encoded_rustflags).unwrap_or_else(|error| {
+        panic!("Linux x64 Node addons must use the x86-64-v2 baseline; {error}")
+    });
 }

nodejs/build_support/x86_64_v2.rs

@@ -0,0 +1,430 @@
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-FileCopyrightText: Copyright The LanceDB Authors
+
+use std::collections::{BTreeMap, BTreeSet};
+
+const SAFE_TARGET_CPUS: [&str; 2] = ["x86-64", "x86-64-v2"];
+const BASELINE_FEATURES: [&str; 9] = [
+    "cmpxchg16b",
+    "fxsr",
+    "popcnt",
+    "sse",
+    "sse2",
+    "sse3",
+    "sse4.1",
+    "sse4.2",
+    "ssse3",
+];
+
+pub(crate) fn validate_encoded_rustflags(encoded: &str) -> Result<(), String> {
+    let mut target_cpu = None;
+    let mut feature_states = BTreeMap::new();
+    let mut required_disables = BTreeSet::new();
+    let mut unsupported_features = BTreeSet::new();
+
+    for option in codegen_options(encoded)? {
+        let Some((name, value)) = option.split_once('=') else {
+            continue;
+        };
+
+        let name = name.replace('_', "-");
+        match name.as_str() {
+            "target-cpu" => target_cpu = Some(value),
+            "target-feature" => {
+                for toggle in value.split(',').filter(|toggle| !toggle.is_empty()) {
+                    let (enabled, feature) = match toggle.as_bytes()[0] {
+                        b'+' => (true, &toggle[1..]),
+                        b'-' => (false, &toggle[1..]),
+                        _ => return Err(format!("invalid target feature flag: {toggle}")),
+                    };
+
+                    feature_states.insert(feature, enabled);
+                    if enabled && !BASELINE_FEATURES.contains(&feature) {
+                        match feature {
+                            // These are inherited from the workspace configuration and
+                            // explicitly canceled by the Node configuration. Account for
+                            // their implied AVX prerequisite as well as the named feature.
+                            "avx" => {
+                                required_disables.insert("avx");
+                            }
+                            "avx2" => {
+                                required_disables.extend(["avx", "avx2"]);
+                            }
+                            "f16c" => {
+                                required_disables.extend(["avx", "f16c"]);
+                            }
+                            "fma" => {
+                                required_disables.extend(["avx", "fma"]);
+                            }
+                            _ => {
+                                unsupported_features.insert(feature);
+                            }
+                        }
+                    }
+                }
+            }
+            // LLVM arguments can independently alter the target feature set and
+            // cannot be proven safe by inspecting rustc's target options.
+            "llvm-args" => return Err("LLVM arguments can override the CPU baseline".to_owned()),
+            _ => {}
+        }
+    }
+
+    if let Some(cpu) = target_cpu.filter(|cpu| !SAFE_TARGET_CPUS.contains(cpu)) {
+        return Err(format!(
+            "effective target CPU is {}, expected x86-64-v2 or lower",
+            cpu
+        ));
+    }
+
+    if !unsupported_features.is_empty() {
+        return Err(format!(
+            "features above v2: {}",
+            unsupported_features
+                .into_iter()
+                .collect::<Vec<_>>()
+                .join(", ")
+        ));
+    }
+
+    let not_disabled = required_disables
+        .into_iter()
+        .filter(|feature| feature_states.get(feature) != Some(&false))
+        .collect::<Vec<_>>();
+    if !not_disabled.is_empty() {
+        return Err(format!(
+            "inherited features not fully disabled: {}",
+            not_disabled.join(", ")
+        ));
+    }
+
+    Ok(())
+}
+
+fn codegen_options(encoded: &str) -> Result<Vec<&str>, String> {
+    let arguments = encoded.split('\u{1f}').collect::<Vec<_>>();
+    if arguments.iter().any(|argument| argument.starts_with('@')) {
+        return Err("rustc response-file arguments cannot be validated".to_owned());
+    }
+
+    let mut options = Vec::new();
+    let mut index = 0;
+
+    while index < arguments.len() {
+        let argument = arguments[index];
+        if argument == "--cfg" {
+            index += 1;
+            let cfg = arguments
+                .get(index)
+                .copied()
+                .ok_or_else(|| "missing value after --cfg".to_owned())?;
+            reject_builtin_target_feature_cfg(cfg)?;
+        } else if let Some(cfg) = argument.strip_prefix("--cfg=") {
+            reject_builtin_target_feature_cfg(cfg)?;
+        } else if argument == "-C" || argument == "--codegen" {
+            index += 1;
+            let option = arguments
+                .get(index)
+                .copied()
+                .ok_or_else(|| format!("missing value after {argument}"))?;
+            options.push(option.trim_start_matches('='));
+        } else if let Some(option) = argument.strip_prefix("-C") {
+            if !option.is_empty() {
+                options.push(option.trim_start_matches('='));
+            }
+        } else if let Some(option) = argument.strip_prefix("--codegen=") {
+            options.push(option);
+        }
+        index += 1;
+    }
+
+    Ok(options)
+}
+
+fn reject_builtin_target_feature_cfg(cfg: &str) -> Result<(), String> {
+    let key = cfg.split_once('=').map_or(cfg, |(key, _)| key);
+    if key.contains("/*") || key.contains("//") {
+        return Err("comment-bearing cfgs cannot be validated".to_owned());
+    }
+    if !key.is_ascii() {
+        return Err("non-ASCII cfg keys cannot be validated".to_owned());
+    }
+
+    let name = key.trim();
+    let name = name.strip_prefix("r#").unwrap_or(name);
+    if name == "target_feature" {
+        return Err("built-in target_feature cfgs can override runtime CPU detection".to_owned());
+    }
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn encoded(arguments: &[&str]) -> String {
+        arguments.join("\u{1f}")
+    }
+
+    #[test]
+    fn accepts_merged_workspace_and_node_flags() {
+        let flags = encoded(&[
+            "-C",
+            "target-cpu=haswell",
+            "-C",
+            "target-feature=+avx2,+fma,+f16c",
+            "-C",
+            "target-cpu=x86-64-v2",
+            "-C",
+            "target-feature=-avx,-avx2,-fma,-f16c",
+        ]);
+
+        assert_eq!(validate_encoded_rustflags(&flags), Ok(()));
+    }
+
+    #[test]
+    fn accepts_non_merging_v2_boundary() {
+        let flags = encoded(&["-Ctarget-cpu=x86-64-v2"]);
+
+        assert_eq!(validate_encoded_rustflags(&flags), Ok(()));
+    }
+
+    #[test]
+    fn accepts_default_cpu_with_non_codegen_flags() {
+        let flags = encoded(&["-D", "warnings"]);
+
+        assert_eq!(validate_encoded_rustflags(&flags), Ok(()));
+    }
+
+    #[test]
+    fn accepts_unrelated_custom_cfg() {
+        let flags = encoded(&["--cfg=tokio_unstable"]);
+
+        assert_eq!(validate_encoded_rustflags(&flags), Ok(()));
+    }
+
+    #[test]
+    fn accepts_comment_like_syntax_in_cfg_value() {
+        let flags = encoded(&[r#"--cfg=endpoint="https://example.com/*""#]);
+
+        assert_eq!(validate_encoded_rustflags(&flags), Ok(()));
+    }
+
+    #[test]
+    fn accepts_explicit_x86_64_v1_cpu() {
+        let flags = encoded(&["-Ctarget-cpu=x86-64"]);
+
+        assert_eq!(validate_encoded_rustflags(&flags), Ok(()));
+    }
+
+    #[test]
+    fn accepts_musl_dynamic_crt_configuration() {
+        let flags = encoded(&[
+            "-C",
+            "target-cpu=haswell",
+            "-C",
+            "target-feature=-crt-static,+avx2,+fma,+f16c",
+            "-C",
+            "target-cpu=x86-64-v2",
+            "-C",
+            "target-feature=-crt-static,-avx,-avx2,-fma,-f16c",
+        ]);
+
+        assert_eq!(validate_encoded_rustflags(&flags), Ok(()));
+    }
+
+    #[test]
+    fn rejects_feature_omitted_from_target_cfg() {
+        let flags = encoded(&["-Ctarget-cpu=x86-64-v2", "-Ctarget-feature=+apxf"]);
+
+        assert_eq!(
+            validate_encoded_rustflags(&flags),
+            Err("features above v2: apxf".to_owned())
+        );
+    }
+
+    #[test]
+    fn rejects_underscore_spelling_above_baseline_feature() {
+        let flags = encoded(&["-Ctarget_cpu=x86-64-v2", "-Ctarget_feature=+apxf"]);
+
+        assert_eq!(
+            validate_encoded_rustflags(&flags),
+            Err("features above v2: apxf".to_owned())
+        );
+    }
+
+    #[test]
+    fn rejects_unexpected_above_baseline_feature() {
+        let flags = encoded(&[
+            "--codegen=target-cpu=x86-64-v2",
+            "--codegen",
+            "target-feature=+bmi2",
+        ]);
+
+        assert_eq!(
+            validate_encoded_rustflags(&flags),
+            Err("features above v2: bmi2".to_owned())
+        );
+    }
+
+    #[test]
+    fn rejects_cpu_above_v2() {
+        let flags = encoded(&["-Ctarget-cpu=haswell"]);
+
+        assert_eq!(
+            validate_encoded_rustflags(&flags),
+            Err("effective target CPU is haswell, expected x86-64-v2 or lower".to_owned())
+        );
+    }
+
+    #[test]
+    fn rejects_incompletely_disabled_feature_implications() {
+        let flags = encoded(&["-Ctarget-cpu=x86-64-v2", "-Ctarget-feature=+avx2,-avx2"]);
+
+        assert_eq!(
+            validate_encoded_rustflags(&flags),
+            Err("inherited features not fully disabled: avx".to_owned())
+        );
+    }
+
+    #[test]
+    fn rejects_llvm_feature_overrides() {
+        let flags = encoded(&["-Ctarget-cpu=x86-64-v2", "-Cllvm-args=-mattr=+apxf"]);
+
+        assert_eq!(
+            validate_encoded_rustflags(&flags),
+            Err("LLVM arguments can override the CPU baseline".to_owned())
+        );
+    }
+
+    #[test]
+    fn rejects_underscore_spelling_llvm_feature_overrides() {
+        let flags = encoded(&["-Ctarget_cpu=x86-64-v2", "-Cllvm_args=-mattr=+apxf"]);
+
+        assert_eq!(
+            validate_encoded_rustflags(&flags),
+            Err("LLVM arguments can override the CPU baseline".to_owned())
+        );
+    }
+
+    #[test]
+    fn rejects_response_file_arguments() {
+        let flags = encoded(&["-Ctarget-cpu=x86-64-v2", "@flags.rsp"]);
+
+        assert_eq!(
+            validate_encoded_rustflags(&flags),
+            Err("rustc response-file arguments cannot be validated".to_owned())
+        );
+    }
+
+    #[test]
+    fn rejects_split_builtin_target_feature_cfg() {
+        let flags = encoded(&[
+            "-Ctarget-cpu=x86-64-v2",
+            "--cfg",
+            r#"target_feature="avx2""#,
+            "-Aexplicit_builtin_cfgs_in_flags",
+        ]);
+
+        assert_eq!(
+            validate_encoded_rustflags(&flags),
+            Err("built-in target_feature cfgs can override runtime CPU detection".to_owned())
+        );
+    }
+
+    #[test]
+    fn rejects_equals_builtin_target_feature_cfg() {
+        let flags = encoded(&[
+            "-Ctarget-cpu=x86-64-v2",
+            r#"--cfg=target_feature="avx2""#,
+            "-Aexplicit_builtin_cfgs_in_flags",
+        ]);
+
+        assert_eq!(
+            validate_encoded_rustflags(&flags),
+            Err("built-in target_feature cfgs can override runtime CPU detection".to_owned())
+        );
+    }
+
+    #[test]
+    fn rejects_raw_identifier_builtin_target_feature_cfg() {
+        let flags = encoded(&[
+            "-Ctarget-cpu=x86-64-v2",
+            r#"--cfg=r#target_feature="avx2""#,
+            "-Aexplicit_builtin_cfgs_in_flags",
+        ]);
+
+        assert_eq!(
+            validate_encoded_rustflags(&flags),
+            Err("built-in target_feature cfgs can override runtime CPU detection".to_owned())
+        );
+    }
+
+    #[test]
+    fn rejects_block_comment_after_cfg_name() {
+        let flags = encoded(&[
+            "--cfg",
+            r#"target_feature/*gate*/="avx2""#,
+            "-Aexplicit_builtin_cfgs_in_flags",
+        ]);
+
+        assert_eq!(
+            validate_encoded_rustflags(&flags),
+            Err("comment-bearing cfgs cannot be validated".to_owned())
+        );
+    }
+
+    #[test]
+    fn rejects_block_comment_before_cfg_name() {
+        let flags = encoded(&[
+            r#"--cfg=/*gate*/target_feature="avx2""#,
+            "-Aexplicit_builtin_cfgs_in_flags",
+        ]);
+
+        assert_eq!(
+            validate_encoded_rustflags(&flags),
+            Err("comment-bearing cfgs cannot be validated".to_owned())
+        );
+    }
+
+    #[test]
+    fn rejects_line_comment_cfg_trivia() {
+        let flags = encoded(&[
+            "--cfg",
+            "target_feature// gate\n=\"avx2\"",
+            "-Aexplicit_builtin_cfgs_in_flags",
+        ]);
+
+        assert_eq!(
+            validate_encoded_rustflags(&flags),
+            Err("comment-bearing cfgs cannot be validated".to_owned())
+        );
+    }
+
+    #[test]
+    fn rejects_leading_bom_in_cfg_key() {
+        let flags = encoded(&[
+            "--cfg",
+            "\u{feff}target_feature=\"avx2\"",
+            "-Aexplicit_builtin_cfgs_in_flags",
+        ]);
+
+        assert_eq!(
+            validate_encoded_rustflags(&flags),
+            Err("non-ASCII cfg keys cannot be validated".to_owned())
+        );
+    }
+
+    #[test]
+    fn rejects_non_ascii_pattern_whitespace_in_cfg_key() {
+        for whitespace in ['\u{200e}', '\u{200f}'] {
+            let cfg = format!("{whitespace}target_feature=\"avx2\"");
+            let flags = encoded(&["--cfg", &cfg, "-Aexplicit_builtin_cfgs_in_flags"]);
+
+            assert_eq!(
+                validate_encoded_rustflags(&flags),
+                Err("non-ASCII cfg keys cannot be validated".to_owned())
+            );
+        }
+    }
+}

nodejs/ci/pre_haswell_smoke.js

@@ -0,0 +1,37 @@
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-FileCopyrightText: Copyright The LanceDB Authors
+
+const assert = require("node:assert/strict");
+const fs = require("node:fs");
+const os = require("node:os");
+const path = require("node:path");
+
+const { connect } = require("../dist");
+
+async function main() {
+  const tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), "lancedb-cpu-"));
+
+  try {
+    const db = await connect(tmpDir);
+    const table = await db.createTable("vectors", [
+      { id: 1, vector: [1, 0, 0] },
+      { id: 2, vector: [0, 1, 0] },
+    ]);
+    const results = await table
+      .vectorSearch([1, 0, 0])
+      .distanceType("cosine")
+      .limit(1)
+      .toArray();
+
+    assert.equal(results.length, 1);
+    assert.equal(results[0].id, 1);
+    assert.ok(Math.abs(results[0]._distance) < 1e-6);
+  } finally {
+    fs.rmSync(tmpDir, { force: true, recursive: true });
+  }
+}
+
+main().catch((error) => {
+  console.error(error);
+  process.exitCode = 1;
+});

nodejs/package.json

@@ -88,6 +88,7 @@
     "lint-fix": "biome check --write . && biome format --write .",
     "prepublishOnly": "napi prepublish -t npm",
     "test": "jest --verbose",
+    "test:pre-haswell": "node ci/pre_haswell_smoke.js",
     "integration": "S3_TEST=1 pnpm test",
     "universal": "napi universalize",
     "version": "napi version"

python/python/lancedb/db.py

@@ -707,6 +707,9 @@ class LanceDBConnection(DBConnection):
         self._namespace_client_properties = namespace_client_properties
         if _inner is not None:
             self._conn = _inner
+            # Native-derived wrappers resolve this in their async reconstruction
+            # path so construction never synchronously re-enters LOOP.
+            self._read_consistency_interval = read_consistency_interval
             self._cached_namespace_client = None
             return
 
@@ -756,11 +759,14 @@ class LanceDBConnection(DBConnection):
         # storage_options.  Also, this class really shouldn't be holding any state
         # beyond _conn.
         self._conn = AsyncConnection(LOOP.run(do_connect()))
+        # Keep property access synchronous so debugger introspection cannot wait on
+        # the background loop while that thread is suspended at a breakpoint.
+        self._read_consistency_interval = read_consistency_interval
         self._cached_namespace_client: Optional[LanceNamespace] = None
 
     @property
     def read_consistency_interval(self) -> Optional[timedelta]:
-        return LOOP.run(self._conn.get_read_consistency_interval())
+        return self._read_consistency_interval
 
     @property
     def session(self) -> Optional[Session]:
@@ -771,8 +777,16 @@ class LanceDBConnection(DBConnection):
         return self._conn.uri
 
     @classmethod
-    def from_inner(cls, inner: LanceDbConnection):
-        return cls(None, _inner=inner)
+    def from_inner(
+        cls,
+        inner: LanceDbConnection,
+        read_consistency_interval: Optional[timedelta],
+    ):
+        return cls(
+            None,
+            read_consistency_interval=read_consistency_interval,
+            _inner=inner,
+        )
 
     def __repr__(self) -> str:
         return f"{self.__class__.__name__}(uri={self._conn.uri!r})"

python/python/lancedb/permutation.py

@@ -226,7 +226,7 @@ class PermutationBuilder:
 
         async def do_execute():
             inner_tbl = await self._async.execute()
-            return LanceTable.from_inner(inner_tbl)
+            return await LanceTable.from_inner(inner_tbl)
 
         return LOOP.run(do_execute())
 

python/python/lancedb/table.py

@@ -2182,11 +2182,15 @@ class LanceTable(Table):
         return self.name
 
     @classmethod
-    def from_inner(cls, tbl: LanceDBTable):
-        from .db import LanceDBConnection
+    async def from_inner(cls, tbl: LanceDBTable):
+        from .db import AsyncConnection, LanceDBConnection
 
         async_tbl = AsyncTable(tbl)
-        conn = LanceDBConnection.from_inner(tbl.database())
+        inner_conn = tbl.database()
+        read_consistency_interval = await AsyncConnection(
+            inner_conn
+        ).get_read_consistency_interval()
+        conn = LanceDBConnection.from_inner(inner_conn, read_consistency_interval)
         return cls(
             conn,
             async_tbl.name,

python/python/tests/test_db.py

@@ -77,6 +77,23 @@ def test_sync_repr_does_not_use_background_loop(tmp_path, monkeypatch):
     assert repr(table) == f"LanceTable(name='test', _conn={db!r})"
 
 
+def test_read_consistency_interval_does_not_use_background_loop(tmp_path, monkeypatch):
+    from lancedb.background_loop import LOOP
+    from lancedb.db import LanceDBConnection
+
+    consistency_interval = timedelta(seconds=5)
+    db = lancedb.connect(tmp_path, read_consistency_interval=consistency_interval)
+    db_from_inner = LanceDBConnection.from_inner(db._inner, consistency_interval)
+
+    def fail_run(*args, **kwargs):
+        raise AssertionError("properties should not use the Python background loop")
+
+    monkeypatch.setattr(LOOP, "run", fail_run)
+
+    assert db.read_consistency_interval == consistency_interval
+    assert db_from_inner.read_consistency_interval == consistency_interval
+
+
 def test_ingest_pd(tmp_path):
     db = lancedb.connect(tmp_path)
 

python/python/tests/test_permutation.py

@@ -6,6 +6,7 @@ import math
 import pytest
 
 from lancedb import DBConnection, Table, connect
+from lancedb.background_loop import LOOP
 from lancedb.permutation import Permutation, Permutations, permutation_builder
 
 
@@ -31,6 +32,25 @@ def test_split_random_ratios(mem_db):
     assert 65 <= split_1_count <= 75  # ~70% ± tolerance
 
 
+def test_execute_does_not_reenter_background_loop(tmp_path, monkeypatch):
+    import threading
+
+    db = connect(tmp_path)
+    tbl = db.create_table("test_table", pa.table({"x": range(10)}))
+    original_run = LOOP.run
+
+    def fail_on_reentry(future):
+        assert threading.current_thread() is not LOOP.thread
+        return original_run(future)
+
+    monkeypatch.setattr(LOOP, "run", fail_on_reentry)
+
+    permutation_tbl = permutation_builder(tbl).execute()
+
+    assert permutation_tbl.count_rows() == 10
+    assert permutation_tbl._conn.read_consistency_interval is None
+
+
 def test_split_random_counts(mem_db):
     """Test random splitting with absolute counts."""
     tbl = mem_db.create_table(

python/python/tests/test_table.py

@@ -6,6 +6,7 @@ import os
 import sys
 import threading
 import warnings
+from concurrent.futures import ThreadPoolExecutor
 from datetime import date, datetime, timedelta
 from time import sleep
 from typing import List
@@ -2124,6 +2125,27 @@ def test_delete(mem_db: DBConnection):
     assert table.to_arrow()["id"].to_pylist() == [1]
 
 
+def test_concurrent_deletes_are_thread_safe(mem_db: DBConnection):
+    num_workers = 8
+    table = mem_db.create_table(
+        "my_table", data=[{"id": row_id} for row_id in range(num_workers)]
+    )
+    barrier = threading.Barrier(num_workers)
+
+    def delete(row_id: int):
+        barrier.wait()
+        return table.delete(f"id = {row_id}")
+
+    with ThreadPoolExecutor(max_workers=num_workers) as pool:
+        results = list(pool.map(delete, range(num_workers)))
+
+    assert all(result.num_deleted_rows == 1 for result in results)
+    assert sorted(result.version for result in results) == list(
+        range(2, num_workers + 2)
+    )
+    assert table.count_rows() == 0
+
+
 def test_delete_expr(mem_db: DBConnection):
     table = mem_db.create_table(
         "my_table",

python/src/table.rs

@@ -745,6 +745,9 @@ impl Table {
 
     #[allow(private_interfaces)]
     pub fn delete(self_: PyRef<'_, Self>, condition: PredicateArg) -> PyResult<Bound<'_, PyAny>> {
+        // Do not hold the Python borrow across the await.  The cloned Rust table
+        // handle is thread-safe and allows deletes on the same Python table to
+        // run concurrently without PyO3 reporting "Already borrowed".
         let inner = self_.inner_ref()?.clone();
         future_into_py(self_.py(), async move {
             let result = match &condition {