Add no-GIL interpreter support

.github/workflows/test.yml

@@ -14,6 +14,7 @@ jobs:
         exclude:
           - os: windows-11-arm
             py: "3.10"
+
     runs-on: ${{ matrix.os }}
     name: Run test with Python ${{ matrix.py }} on ${{ matrix.os }}
 
@@ -33,22 +34,41 @@ jobs:
         run: |
           python -m pip install -r requirements.txt pytest
 
+      - name: Install pytest-run-parallel under free-threading
+        if: contains(matrix.py, 't')
+        run: |
+          pip install pytest-run-parallel
+
       - name: Build
         shell: bash
         run: |
           make cython
           pip install .
 
       - name: Test (C extension)
+        if: ${{ ! contains(matrix.py, 't') }}
         shell: bash
         run: |
           pytest -v test
 
       - name: Test (pure Python fallback)
+        if: ${{ ! contains(matrix.py, 't') }}
         shell: bash
         run: |
           MSGPACK_PUREPYTHON=1 pytest -v test
 
+      - name: Test (C extension) in parallel under free-threading
+        if: contains(matrix.py, 't')
+        shell: bash
+        run: |
+          pytest -v --parallel-threads=auto --iterations=20 test
+
+      - name: Test (pure Python fallback) in parallel under free-threading
+        if: contains(matrix.py, 't')
+        shell: bash
+        run: |
+          MSGPACK_PUREPYTHON=1 pytest -v --parallel-threads=auto --iterations=20 test
+
       - name: build packages
         shell: bash
         run: |

test/uneeded_test_multithreading.py

@@ -0,0 +1,51 @@
+#!/usr/bin/env python3
+import threading
+from concurrent.futures import ThreadPoolExecutor
+
+from msgpack import Packer
+
+
+def run_threaded(
+    func,
+    num_threads=8,
+    pass_count=False,
+    pass_barrier=False,
+    outer_iterations=1,
+    prepare_args=None,
+):
+    """Runs a function many times in parallel"""
+    for _ in range(outer_iterations):
+        with ThreadPoolExecutor(max_workers=num_threads) as tpe:
+            if prepare_args is None:
+                args = []
+            else:
+                args = prepare_args()
+            if pass_barrier:
+                barrier = threading.Barrier(num_threads)
+                args.append(barrier)
+            if pass_count:
+                all_args = [(func, i, *args) for i in range(num_threads)]
+            else:
+                all_args = [(func, *args) for i in range(num_threads)]
+            try:
+                futures = []
+                for arg in all_args:
+                    futures.append(tpe.submit(*arg))
+            finally:
+                if len(futures) < num_threads and pass_barrier:
+                    barrier.abort()
+            for f in futures:
+                f.result()
+
+
+def test_multithread_packing():
+    output = []
+    test_data = "abcd" * 10_000_000
+    packer = Packer()
+
+    def closure(b):
+        data = packer.pack(test_data)
+        output.append(data)
+        b.wait()
+
+    run_threaded(closure, num_threads=10, pass_barrier=True, pass_count=False)