fix(google-crc32c): release GIL for large buffers in crc32c operations

packages/google-crc32c/src/google_crc32c/_crc32c.c

@@ -2,6 +2,16 @@
 #include <Python.h>
 #include <crc32c/crc32c.h>
 
+/* The minimum buffer size in bytes (1MB) required to justify the overhead of releasing the GIL. */
+static const Py_ssize_t gil_threshold = 1024 * 1024;
+
+static int
+_should_release_gil(Py_ssize_t length, PyObject *chunk_obj)
+{
+    /* Checks if the chunk is immutable (bytes) to prevent concurrent modification,
+     * and large enough to benefit from releasing the GIL. */
+    return (length >= gil_threshold && PyBytes_Check(chunk_obj));
+}
 
 static PyObject *
 _crc32c_extend(PyObject *self, PyObject *args)
@@ -10,12 +20,21 @@ _crc32c_extend(PyObject *self, PyObject *args)
     uint32_t crc;
     const char *chunk;
     Py_ssize_t length;
+    PyThreadState *save = NULL;
 
     if (!PyArg_ParseTuple(args, "ky#", &crc_input, &chunk, &length))
         return NULL;
 
+    if (_should_release_gil(length, PyTuple_GET_ITEM(args, 1))) {
+        save = PyEval_SaveThread();
+    }
+
     crc = crc32c_extend((uint32_t)crc_input, (const uint8_t*)chunk, length);
 
+    if (save) {
+        PyEval_RestoreThread(save);
+    }
+
     return PyLong_FromUnsignedLong(crc);
 }
 
@@ -26,12 +45,21 @@ _crc32c_value(PyObject *self, PyObject *args)
     uint32_t crc;
     const char *chunk;
     Py_ssize_t length;
+    PyThreadState *save = NULL;
 
     if (!PyArg_ParseTuple(args, "y#", &chunk, &length))
         return NULL;
 
+    if (_should_release_gil(length, PyTuple_GET_ITEM(args, 0))) {
+        save = PyEval_SaveThread();
+    }
+
     crc = crc32c_value((const uint8_t*)chunk, length);
 
+    if (save) {
+        PyEval_RestoreThread(save);
+    }
+
     return PyLong_FromUnsignedLong(crc);
 }