Improve: Unlock GIL in Str.write_to

Closes ashvardanian#105

Author: ashvardanian

python/lib.c

@@ -1272,15 +1272,21 @@ static PyObject *Str_write_to(PyObject *self, PyObject *args, PyObject *kwargs)
     }
     memcpy(path_buffer, path.start, path.length);
 
+    // Unlock the Global Interpreter Lock (GIL) to allow other threads to run
+    // while the current thread is waiting for the file to be written.
+    PyThreadState *gil_state = PyEval_SaveThread();
     FILE *file_pointer = fopen(path_buffer, "wb");
     if (file_pointer == NULL) {
+        PyEval_RestoreThread(gil_state);
         PyErr_SetFromErrnoWithFilename(PyExc_OSError, path_buffer);
         free(path_buffer);
+        PyEval_RestoreThread(gil_state);
         return NULL;
     }
 
     setbuf(file_pointer, NULL); // Set the stream to unbuffered
     int status = fwrite(text.start, 1, text.length, file_pointer);
+    PyEval_RestoreThread(gil_state);
     if (status != text.length) {
         PyErr_SetFromErrnoWithFilename(PyExc_OSError, path_buffer);
         free(path_buffer);

scripts/test.py

@@ -1,6 +1,8 @@
 from random import choice, randint
 from string import ascii_lowercase
 from typing import Optional
+import tempfile
+import os
 
 import pytest
 
@@ -104,6 +106,25 @@ def test_unit_buffer_protocol():
     assert "".join([c.decode("utf-8") for c in arr.tolist()]) == "hello"
 
 
+def test_str_write_to():
+    native = "line1\nline2\nline3"
+    big = Str(native)  # Assuming Str is your custom class
+
+    # Create a temporary file
+    with tempfile.NamedTemporaryFile(delete=False) as tmpfile:
+        temp_filename = tmpfile.name  # Store the name for later use
+
+    try:
+        big.write_to(temp_filename)
+        with open(temp_filename, "r") as file:
+            content = file.read()
+            assert (
+                content == native
+            ), "The content of the file does not match the expected output"
+    finally:
+        os.remove(temp_filename)
+
+
 def test_unit_split():
     native = "line1\nline2\nline3"
     big = Str(native)