Release GIL while resampling

Fixes #13.

Author: tuxu

src/samplerate.cpp

@@ -179,7 +179,10 @@ class Resampler {
         sr_ratio       // src_ratio, sampling rate conversion ratio
     };
 
-    error_handler(src_process(_state, &src_data));
+    error_handler([&]() {
+      py::gil_scoped_release release;
+      return src_process(_state, &src_data);
+    }());
 
     // create a shorter view of the array
     if ((size_t)src_data.output_frames_gen < new_size) {
@@ -294,8 +297,11 @@ class CallbackResampler {
     if (_state == nullptr) _create();
 
     // read from the callback
-    size_t output_frames_gen = src_callback_read(
-        _state, _ratio, (long)frames, static_cast<float *>(outbuf.ptr));
+    size_t output_frames_gen = [&]() {
+      py::gil_scoped_release release;
+      return src_callback_read(_state, _ratio, (long)frames,
+                               static_cast<float *>(outbuf.ptr));
+    }();
 
     // check error status
     if (output_frames_gen == 0) {
@@ -407,9 +413,10 @@ py::array_t<float, py::array::c_style> resample(
       sr_ratio  // src_ratio, sampling rate conversion ratio
   };
 
-  int ret_code = src_simple(&src_data, converter_type_int, channels);
-
-  error_handler(ret_code);
+  error_handler([&]() {
+    py::gil_scoped_release release;
+    return src_simple(&src_data, converter_type_int, channels);
+  }());
 
   // create a shorter view of the array
   if ((size_t)src_data.output_frames_gen < new_size) {