utils.rs

// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

use std::future::Future;
use std::sync::{Arc, OnceLock};
use std::time::Duration;

use datafusion::common::ScalarValue;
use datafusion::datasource::TableProvider;
use datafusion::execution::context::SessionContext;
use datafusion::logical_expr::Volatility;
use datafusion_ffi::table_provider::{FFI_TableProvider, ForeignTableProvider};
use pyo3::exceptions::PyValueError;
use pyo3::prelude::*;
use pyo3::types::PyCapsule;
use tokio::runtime::Runtime;
use tokio::task::JoinHandle;
use tokio::time::sleep;

use crate::common::data_type::PyScalarValue;
use crate::errors::{py_datafusion_err, to_datafusion_err, PyDataFusionError, PyDataFusionResult};
use crate::TokioRuntime;

/// Utility to get the Tokio Runtime from Python
#[inline]
pub(crate) fn get_tokio_runtime() -> &'static TokioRuntime {
    // NOTE: Other pyo3 python libraries have had issues with using tokio
    // behind a forking app-server like `gunicorn`
    // If we run into that problem, in the future we can look to `delta-rs`
    // which adds a check in that disallows calls from a forked process
    // https://github.com/delta-io/delta-rs/blob/87010461cfe01563d91a4b9cd6fa468e2ad5f283/python/src/utils.rs#L10-L31
    static RUNTIME: OnceLock<TokioRuntime> = OnceLock::new();
    RUNTIME.get_or_init(|| TokioRuntime(tokio::runtime::Runtime::new().unwrap()))
}

#[inline]
pub(crate) fn is_ipython_env(py: Python) -> &'static bool {
    static IS_IPYTHON_ENV: OnceLock<bool> = OnceLock::new();
    IS_IPYTHON_ENV.get_or_init(|| {
        py.import("IPython")
            .and_then(|ipython| ipython.call_method0("get_ipython"))
            .map(|ipython| !ipython.is_none())
            .unwrap_or(false)
    })
}

/// Utility to get the Global Datafussion CTX
#[inline]
pub(crate) fn get_global_ctx() -> &'static SessionContext {
    static CTX: OnceLock<SessionContext> = OnceLock::new();
    CTX.get_or_init(SessionContext::new)
}

/// Utility to collect rust futures with GIL released and respond to
/// Python interrupts such as ``KeyboardInterrupt``. If a signal is
/// received while the future is running, the future is aborted and the
/// corresponding Python exception is raised.
pub fn wait_for_future<F>(py: Python, fut: F) -> PyResult<F::Output>
where
    F: Future + Send,
    F::Output: Send,
{
    let runtime: &Runtime = &get_tokio_runtime().0;
    const INTERVAL_CHECK_SIGNALS: Duration = Duration::from_millis(1_000);

    // Some fast running processes that generate many `wait_for_future` calls like
    // PartitionedDataFrameStreamReader::next require checking for interrupts early
    py.run(cr"pass", None, None)?;
    py.check_signals()?;

    py.detach(|| {
        runtime.block_on(async {
            tokio::pin!(fut);
            loop {
                tokio::select! {
                    res = &mut fut => break Ok(res),
                    _ = sleep(INTERVAL_CHECK_SIGNALS) => {
                        Python::attach(|py| {
                                // Execute a no-op Python statement to trigger signal processing.
                                // This is necessary because py.check_signals() alone doesn't
                                // actually check for signals - it only raises an exception if
                                // a signal was already set during a previous Python API call.
                                // Running even trivial Python code forces the interpreter to
                                // process any pending signals (like KeyboardInterrupt).
                                py.run(cr"pass", None, None)?;
                                py.check_signals()
                        })?;
                    }
                }
            }
        })
    })
}

/// Spawn a [`Future`] on the Tokio runtime and wait for completion
/// while respecting Python signal handling.
pub(crate) fn spawn_future<F, T>(py: Python, fut: F) -> PyDataFusionResult<T>
where
    F: Future<Output = datafusion::common::Result<T>> + Send + 'static,
    T: Send + 'static,
{
    let rt = &get_tokio_runtime().0;
    let handle: JoinHandle<datafusion::common::Result<T>> = rt.spawn(fut);
    // Wait for the join handle while respecting Python signal handling.
    // We handle errors in two steps so `?` maps the error types correctly:
    // 1) convert any Python-related error from `wait_for_future` into `PyDataFusionError`
    // 2) convert any DataFusion error (inner result) into `PyDataFusionError`
    let inner_result = wait_for_future(py, async {
        // handle.await yields `Result<datafusion::common::Result<T>, JoinError>`
        // map JoinError into a DataFusion error so the async block returns
        // `datafusion::common::Result<T>` (i.e. Result<T, DataFusionError>)
        match handle.await {
            Ok(inner) => inner,
            Err(join_err) => Err(to_datafusion_err(join_err)),
        }
    })?; // converts PyErr -> PyDataFusionError

    // `inner_result` is `datafusion::common::Result<T>`; use `?` to convert
    // the inner DataFusion error into `PyDataFusionError` via `From` and
    // return the inner `T` on success.
    Ok(inner_result?)
}

pub(crate) fn parse_volatility(value: &str) -> PyDataFusionResult<Volatility> {
    Ok(match value {
        "immutable" => Volatility::Immutable,
        "stable" => Volatility::Stable,
        "volatile" => Volatility::Volatile,
        value => {
            return Err(PyDataFusionError::Common(format!(
                "Unsupported volatility type: `{value}`, supported \
                 values are: immutable, stable and volatile."
            )))
        }
    })
}

pub(crate) fn validate_pycapsule(capsule: &Bound<PyCapsule>, name: &str) -> PyResult<()> {
    let capsule_name = capsule.name()?;
    if capsule_name.is_none() {
        return Err(PyValueError::new_err(format!(
            "Expected {name} PyCapsule to have name set."
        )));
    }

    let capsule_name = capsule_name.unwrap().to_str()?;
    if capsule_name != name {
        return Err(PyValueError::new_err(format!(
            "Expected name '{name}' in PyCapsule, instead got '{capsule_name}'"
        )));
    }

    Ok(())
}

pub(crate) fn table_provider_from_pycapsule(
    obj: &Bound<PyAny>,
) -> PyResult<Option<Arc<dyn TableProvider>>> {
    if obj.hasattr("__datafusion_table_provider__")? {
        let capsule = obj.getattr("__datafusion_table_provider__")?.call0()?;
        let capsule = capsule.downcast::<PyCapsule>().map_err(py_datafusion_err)?;
        validate_pycapsule(capsule, "datafusion_table_provider")?;

        let provider = unsafe { capsule.reference::<FFI_TableProvider>() };
        let provider: ForeignTableProvider = provider.into();

        Ok(Some(Arc::new(provider)))
    } else {
        Ok(None)
    }
}

pub(crate) fn py_obj_to_scalar_value(py: Python, obj: Py<PyAny>) -> PyResult<ScalarValue> {
    // convert Python object to PyScalarValue to ScalarValue

    let pa = py.import("pyarrow")?;

    // Convert Python object to PyArrow scalar
    let scalar = pa.call_method1("scalar", (obj,))?;

    // Convert PyArrow scalar to PyScalarValue
    let py_scalar = PyScalarValue::extract_bound(scalar.as_ref())
        .map_err(|e| PyValueError::new_err(format!("Failed to extract PyScalarValue: {e}")))?;

    // Convert PyScalarValue to ScalarValue
    Ok(py_scalar.into())
}