fix: make sure always have GIL when creating subinterpreter

src/coverage.rs

@@ -8,7 +8,7 @@ use std::collections::{BTreeSet, HashMap};
 use std::ffi::CString;
 use std::{fs, path};
 
-use crate::python::{self, PyObject};
+use crate::python::{self, Interpreter, PyObject};
 
 /// Enables line coverage collection, and returns the tracer object
 pub fn enable_collection() -> PyObject {
@@ -103,6 +103,7 @@ impl FromIterator<(String, BTreeSet<i32>)> for Lines {
 /// not be reported but are still executed. So we need to find which lines could be run,
 /// rather than just the range of the file.
 pub fn get_executable_lines(
+  interpreter: &Interpreter,
   coverage_include: &[path::PathBuf],
   coverage_exclude: &[path::PathBuf],
 ) -> Lines {
@@ -147,7 +148,7 @@ pub fn get_executable_lines(
 
       // as we are compiling python, we need an interpreter
       let line_numbers =
-        python::SubInterpreter::new().run(|| get_line_numbers_for_python_file(&path));
+        python::SubInterpreter::new(interpreter).run(|| get_line_numbers_for_python_file(&path));
 
       if line_numbers.is_empty() {
         None

src/main.rs

@@ -86,14 +86,14 @@ fn main() -> ExitCode {
   reporter.discovered(&discovered);
 
   // Main Python interpreter must be initialized in the main thread
-  let _interpreter = python::Interpreter::initialize();
+  let interpreter = python::Interpreter::initialize();
 
   // Run tests
   let results: TestSummary = discovered
     .tests
     .par_iter()
     .map(|test| {
-      let mut subinterpreter = python::SubInterpreter::new();
+      let mut subinterpreter = python::SubInterpreter::new(&interpreter);
 
       if args.coverage.enabled {
         subinterpreter.enable_coverage();
@@ -131,7 +131,8 @@ fn main() -> ExitCode {
       &args.coverage.exclude
     };
 
-    let possible_lines = coverage::get_executable_lines(coverage_include, coverage_exclude);
+    let possible_lines =
+      coverage::get_executable_lines(&interpreter, coverage_include, coverage_exclude);
     coverage::print_summary(&possible_lines, &results.executed_lines);
   }
 

src/python.rs

@@ -63,6 +63,7 @@ impl Drop for Interpreter {
     unsafe { ffi::Py_FinalizeEx() };
   }
 }
+unsafe impl Sync for Interpreter {}
 
 /// Represents a Python Subinterpreter (An interpreter for a specific thread)
 pub struct SubInterpreter {
@@ -84,12 +85,13 @@ impl SubInterpreter {
   /// Creates a new subinterpreter
   ///
   /// SAFETY: The main interpreter must have been initialized
-  pub fn new() -> Self {
+  pub fn new(main_interpreter: &Interpreter) -> Self {
     let mut interpreter_state = std::ptr::null_mut();
 
     unsafe {
+      ffi::PyEval_RestoreThread(main_interpreter.main_thread_state); // Get the GIL
       ffi::Py_NewInterpreterFromConfig(&mut interpreter_state, &Self::DEFAULT_CONFIG);
-      ffi::PyEval_SaveThread(); // Stops Deadlock
+      ffi::PyEval_SaveThread(); // Release the GIL
     };
 
     Self {