From e37c2268a69edd823d2e67d90fe48c3bc7fba706 Mon Sep 17 00:00:00 2001
From: Sam Haves <shaves@google.com>
Date: Fri, 9 Jan 2026 09:49:24 -0800
Subject: [PATCH] Release gil when compiling spec.

When compiling with threading, we will block the main thread anyways waiting for all threads to complete.

PiperOrigin-RevId: 854230560
Change-Id: Ief689d381afaa3aacc5d712a8df0cb4b6762251c
---
 python/mujoco/specs_wrapper.cc | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/python/mujoco/specs_wrapper.cc b/python/mujoco/specs_wrapper.cc
index 01f9a767..f1ba1188 100644
--- a/python/mujoco/specs_wrapper.cc
+++ b/python/mujoco/specs_wrapper.cc
@@ -89,7 +89,12 @@ MjSpec::~MjSpec() { mj_deleteSpec(ptr); }
 
 raw::MjModel* MjSpec::Compile() {
   if (assets.empty()) {
-    auto m = mj_compile(ptr, 0);
+    raw::MjModel* m;
+    {
+      // Release GIL before calling mj_compile which may spawn threads
+      py::gil_scoped_release no_gil;
+      m = mj_compile(ptr, 0);
+    }
     if (!m || mjs_isWarning(ptr)) {
       throw py::value_error(mjs_getError(ptr));
     }
@@ -112,7 +117,13 @@ raw::MjModel* MjSpec::Compile() {
       }
     }
   }
-  auto m = mj_compile(ptr, &vfs);
+
+  raw::MjModel* m;
+  {
+    // Release GIL before calling mj_compile which may spawn threads
+    py::gil_scoped_release no_gil;
+    m = mj_compile(ptr, &vfs);
+  }
   mj_deleteVFS(&vfs);
   if (!m || mjs_isWarning(ptr)) {
     throw py::value_error(mjs_getError(ptr));