From 61acf98aec8e4304bff88a73bc8ca463234d285b Mon Sep 17 00:00:00 2001
From: Daniel Grunwald <daniel@danielgrunwald.de>
Date: Sun, 4 Jan 2015 20:11:18 +0100
Subject: [PATCH] Fix threading

---
 src/conversion.rs | 19 ++++++++++---------
 src/err.rs        |  1 -
 src/lib.rs        |  1 +
 src/pythonrun.rs  | 31 +++++++++++++++++++++++++------
 4 files changed, 36 insertions(+), 16 deletions(-)

diff --git a/src/conversion.rs b/src/conversion.rs
index 486514be..2659beb1 100644
--- a/src/conversion.rs
+++ b/src/conversion.rs
@@ -79,9 +79,9 @@ impl <'p, 's, T : PythonObject<'p>> ToPyObject<'p, 's> for T {
     }
 }
 
-impl <'p, 'a, T : PythonObject<'p>> FromPyObject<'p, 'a> for &'a T {
+impl <'p, 's, T : PythonObject<'p>> FromPyObject<'p, 's> for &'s T {
     #[inline]
-    fn from_py_object(s: &'a PyObject<'p>) -> PyResult<'p, &'a T> {
+    fn from_py_object(s: &'s PyObject<'p>) -> PyResult<'p, &'s T> {
         s.downcast()
     }
 }
@@ -100,23 +100,24 @@ impl <'p, 's, T : PythonObject<'p>> ToPyObject<'p, 's> for PyPtr<'p, T> {
     }
 }
 
-impl <'p, 'a, T : PythonObject<'p>> FromPyObject<'p, 'a> for PyPtr<'p, T> {
+impl <'p, 's, T : PythonObject<'p>> FromPyObject<'p, 's> for PyPtr<'p, T> {
     #[inline]
-    fn from_py_object(s : &'a PyObject<'p>) -> PyResult<'p, PyPtr<'p, T>> {
+    fn from_py_object(s : &'s PyObject<'p>) -> PyResult<'p, PyPtr<'p, T>> {
         PyPtr::new(s).downcast_into()
     }
 }
 
 // bool
 
-/*
-impl <'p, T : PythonObject<'p>> ToPyObject<'p> for bool {
+
+impl <'p, 's> ToPyObject<'p, 's> for bool {
     type PointerType = &'p PyObject<'p>;
     
-    fn to_py_object(&self, py: Python<'p>) -> PyResult<'p, Self::PointerType>;
-        if *self { py.True() } else { py.False() }
+    #[inline]
+    fn to_py_object(&'s self, py: Python<'p>) -> PyResult<'p, &'p PyObject<'p>> {
+        Ok(if *self { py.True() } else { py.False() })
+    }
 }
-*/
 
 impl <'p, 'a> FromPyObject<'p, 'a> for bool {
     fn from_py_object(s: &'a PyObject<'p>) -> PyResult<'p, bool> {
diff --git a/src/err.rs b/src/err.rs
index ea02f2fc..5948e3a1 100644
--- a/src/err.rs
+++ b/src/err.rs
@@ -91,7 +91,6 @@ pub fn error_on_minusone(py : Python, result : libc::c_int) -> PyResult<()> {
 }
 
 #[cfg(test)]
-#[allow(experimental)]
 mod tests {
     use {Python, PyType, PyErr};
     
diff --git a/src/lib.rs b/src/lib.rs
index 1380068c..50e74316 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -2,6 +2,7 @@
 #![allow(unused_imports, dead_code, unused_variables)]
 #![feature(associated_types)]
 #![feature(globs)]
+#![feature(slicing_syntax)]
 
 extern crate libc;
 extern crate "libpython27-sys" as ffi;
diff --git a/src/pythonrun.rs b/src/pythonrun.rs
index 466da97d..7c2a3a5b 100644
--- a/src/pythonrun.rs
+++ b/src/pythonrun.rs
@@ -7,15 +7,34 @@ static START: Once = ONCE_INIT;
 
 /// Prepares the use of python in a free-threaded context.
 pub fn prepare_freethreaded_python() {
+    // Protect against race conditions when python is not yet initialized
+    // and multiple threads concurrently call 'prepare_freethreaded_python()'.
+    // Note that we do not protect against concurrent initialization of the python runtime
+    // by other users of the python C API.
     START.call_once(|| unsafe {
-        ::ffi::Py_InitializeEx(0);
-        if ::ffi::PyEval_ThreadsInitialized() == 0 {
-            ::ffi::PyEval_InitThreads();
-            // InitThreads() will acquire the GIL,
-            // but we don't want to acquire it at this point
+        if ffi::Py_IsInitialized() != 0 {
+            // If python is already initialized, we expect python threading to also be initialized,
+            // as we can't make the existing python main thread acquire the GIL.
+            assert!(ffi::PyEval_ThreadsInitialized() != 0);
+        } else {
+            // If python isn't initialized yet, we expect that python threading isn't initialized either.
+            assert!(ffi::PyEval_ThreadsInitialized() == 0);
+            // Initialize python.
+            // We use Py_InitializeEx() with initsigs=0 to disable Python signal handling.
+            // Signal handling depends on the notion of a 'main thread', which doesn't exist in this case.
+            // Note that the 'main thread' notion in python isn't documented properly;
+            // and running python without one is not officially supported.
+            ffi::Py_InitializeEx(0);
+            ffi::PyEval_InitThreads();
+            // PyEval_InitThreads() will acquire the GIL,
+            // but we don't want to hold it at this point
             // (it's not acquired in the other code paths)
-            ::ffi::PyEval_ReleaseLock();
+            // So immediately release the GIL:
+            let _thread_state = ffi::PyEval_SaveThread();
+            // Note that the PyThreadState returned by PyEval_SaveThread is also held in TLS by the python runtime,
+            // and will be restored by PyGILState_Ensure.
         }
     });
 }
 
+