From f9e6b8d86c4d9c9f0109089c7116f4e4c9cca042 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Tue, 24 Jan 2023 12:30:51 -0700
Subject: [PATCH 1/3] Swap the "auto TSS" tstate too.

---
 Python/pystate.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Python/pystate.c b/Python/pystate.c
index 8bb49d954a81b6..275fe8217e8653 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -1750,6 +1750,9 @@ _PyThreadState_Swap(_PyRuntimeState *runtime, PyThreadState *newts)
             if (check && check->interp == newts->interp) {
                 Py_FatalError("Invalid thread state for this thread");
             }
+            // Make sure the "autoTSS" thread state matches the current one.
+            // XXX Call bind_gilstate_tstate() instead?
+            giltstate_tss_set(runtime, newts);
         }
     }
     errno = err;

From 3e8c3efcd85f7d22a5e3fc191d1d1c12d25feda7 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Wed, 25 Jan 2023 11:17:51 -0700
Subject: [PATCH 2/3] Do not bail out in bind_gilstate_tstate() if it's already
 set.

---
 Python/pystate.c | 28 ++++------------------------
 1 file changed, 4 insertions(+), 24 deletions(-)

diff --git a/Python/pystate.c b/Python/pystate.c
index 275fe8217e8653..ed8c2e212a5539 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -266,10 +266,10 @@ unbind_tstate(PyThreadState *tstate)
    thread state for an OS level thread is when there are multiple
    interpreters.
 
-   The PyGILState_*() APIs don't work with multiple
-   interpreters (see bpo-10915 and bpo-15751), so this function
-   sets TSS only once.  Thus, the first thread state created for that
-   given OS level thread will "win", which seems reasonable behaviour.
+   Before 3.12, the PyGILState_*() APIs didn't work with multiple
+   interpreters (see bpo-10915 and bpo-15751), so this function used
+   to set TSS only once.  Thus, the first thread state created for that
+   given OS level thread would "win", which seemed reasonable behaviour.
 */
 
 static void
@@ -286,10 +286,6 @@ bind_gilstate_tstate(PyThreadState *tstate)
     assert(tstate != tcur);
 
     if (tcur != NULL) {
-        // The original gilstate implementation only respects the
-        // first thread state set.
-        // XXX Skipping like this does not play nice with multiple interpreters.
-        return;
         tcur->_status.bound_gilstate = 0;
     }
     gilstate_tss_set(runtime, tstate);
@@ -1738,23 +1734,7 @@ _PyThreadState_Swap(_PyRuntimeState *runtime, PyThreadState *newts)
         tstate_activate(newts);
     }
 
-    /* It should not be possible for more than one thread state
-       to be used for a thread.  Check this the best we can in debug
-       builds.
-    */
-    // XXX The above isn't true when multiple interpreters are involved.
 #if defined(Py_DEBUG)
-    if (newts && gilstate_tss_initialized(runtime)) {
-        PyThreadState *check = gilstate_tss_get(runtime);
-        if (check != newts) {
-            if (check && check->interp == newts->interp) {
-                Py_FatalError("Invalid thread state for this thread");
-            }
-            // Make sure the "autoTSS" thread state matches the current one.
-            // XXX Call bind_gilstate_tstate() instead?
-            giltstate_tss_set(runtime, newts);
-        }
-    }
     errno = err;
 #endif
     return oldts;

From 631c872c0bd66aeeac5c99fa90999d9a9a92fadd Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 30 Jan 2023 11:56:19 -0700
Subject: [PATCH 3/3] Add a NEWS entry.

---
 .../2023-01-30-11-56-09.gh-issue-59956.7xqnC_.rst              | 3 +++
 1 file changed, 3 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Core and Builtins/2023-01-30-11-56-09.gh-issue-59956.7xqnC_.rst

diff --git a/Misc/NEWS.d/next/Core and Builtins/2023-01-30-11-56-09.gh-issue-59956.7xqnC_.rst b/Misc/NEWS.d/next/Core and Builtins/2023-01-30-11-56-09.gh-issue-59956.7xqnC_.rst
new file mode 100644
index 00000000000000..b3c1896b9493e1
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2023-01-30-11-56-09.gh-issue-59956.7xqnC_.rst	
@@ -0,0 +1,3 @@
+The GILState API is now partially compatible with subinterpreters.
+Previously, ``PyThreadState_GET()`` and ``PyGILState_GetThisThreadState()``
+would get out of sync, causing inconsistent behavior and crashes.