NPY loading segfault bug (#34)

* Fixed Gil semantics in loading and saving from python file streams

python/src/load.cpp

@@ -11,8 +11,6 @@
 #include <unordered_map>
 #include <vector>
 
-#include <iostream>
-
 #include "mlx/load.h"
 #include "mlx/ops.h"
 #include "mlx/utils.h"
@@ -99,26 +97,54 @@ class PyFileReader : public io::Reader {
         seek_func_(file.attr("seek")),
         tell_func_(file.attr("tell")) {}
 
+  ~PyFileReader() {
+    py::gil_scoped_acquire gil;
+
+    pyistream_.release().dec_ref();
+    readinto_func_.release().dec_ref();
+    seek_func_.release().dec_ref();
+    tell_func_.release().dec_ref();
+  }
+
   bool is_open() const override {
-    return !pyistream_.attr("closed").cast<bool>();
+    bool out;
+    {
+      py::gil_scoped_acquire gil;
+      out = !pyistream_.attr("closed").cast<bool>();
+    }
+    return out;
   }
 
   bool good() const override {
-    return !pyistream_.is_none();
+    bool out;
+    {
+      py::gil_scoped_acquire gil;
+      out = !pyistream_.is_none();
+    }
+    return out;
   }
 
   size_t tell() const override {
-    return tell_func_().cast<size_t>();
+    size_t out;
+    {
+      py::gil_scoped_acquire gil;
+      out = tell_func_().cast<size_t>();
+    }
+    return out;
   }
 
   void seek(int64_t off, std::ios_base::seekdir way = std::ios_base::beg)
       override {
+    py::gil_scoped_acquire gil;
     seek_func_(off, (int)way);
   }
 
   void read(char* data, size_t n) override {
+    py::gil_scoped_acquire gil;
+
     py::object bytes_read =
         readinto_func_(py::memoryview::from_buffer(data, {n}, {sizeof(char)}));
+
     if (bytes_read.is_none() || py::cast<size_t>(bytes_read) < n) {
       throw std::runtime_error("[load] Failed to read from python stream");
     }
@@ -163,6 +189,7 @@ DictOrArray mlx_load_helper(py::object file, StreamOrDevice s) {
 
     // If we don't own the stream and it was passed to us, eval immediately
     for (auto& [key, arr] : array_dict) {
+      py::gil_scoped_release gil;
       arr.eval();
     }
 
@@ -172,7 +199,10 @@ DictOrArray mlx_load_helper(py::object file, StreamOrDevice s) {
   } else if (is_istream_object(file)) {
     // If we don't own the stream and it was passed to us, eval immediately
     auto arr = load(std::make_shared<PyFileReader>(file), s);
-    arr.eval();
+    {
+      py::gil_scoped_release gil;
+      arr.eval();
+    }
     return {arr};
   }
 
@@ -192,26 +222,54 @@ class PyFileWriter : public io::Writer {
         seek_func_(file.attr("seek")),
         tell_func_(file.attr("tell")) {}
 
+  ~PyFileWriter() {
+    py::gil_scoped_acquire gil;
+
+    pyostream_.release().dec_ref();
+    write_func_.release().dec_ref();
+    seek_func_.release().dec_ref();
+    tell_func_.release().dec_ref();
+  }
+
   bool is_open() const override {
-    return !pyostream_.attr("closed").cast<bool>();
+    bool out;
+    {
+      py::gil_scoped_acquire gil;
+      out = !pyostream_.attr("closed").cast<bool>();
+    }
+    return out;
   }
 
   bool good() const override {
-    return !pyostream_.is_none();
+    bool out;
+    {
+      py::gil_scoped_acquire gil;
+      out = !pyostream_.is_none();
+    }
+    return out;
   }
 
   size_t tell() const override {
-    return tell_func_().cast<size_t>();
+    size_t out;
+    {
+      py::gil_scoped_acquire gil;
+      out = tell_func_().cast<size_t>();
+    }
+    return out;
   }
 
   void seek(int64_t off, std::ios_base::seekdir way = std::ios_base::beg)
       override {
+    py::gil_scoped_acquire gil;
     seek_func_(off, (int)way);
   }
 
   void write(const char* data, size_t n) override {
+    py::gil_scoped_acquire gil;
+
     py::object bytes_written =
         write_func_(py::memoryview::from_buffer(data, {n}, {sizeof(char)}));
+
     if (bytes_written.is_none() || py::cast<size_t>(bytes_written) < n) {
       throw std::runtime_error("[load] Failed to write to python stream");
     }
@@ -233,7 +291,12 @@ void mlx_save_helper(py::object file, array a, bool retain_graph) {
     save(py::cast<std::string>(file), a, retain_graph);
     return;
   } else if (is_ostream_object(file)) {
-    save(std::make_shared<PyFileWriter>(file), a, retain_graph);
+    auto writer = std::make_shared<PyFileWriter>(file);
+    {
+      py::gil_scoped_release gil;
+      save(writer, a, retain_graph);
+    }
+
     return;
   }
 
@@ -285,7 +348,11 @@ void mlx_savez_helper(
   for (auto [k, a] : arrays_dict) {
     std::string fname = k + ".npy";
     auto py_ostream = zipfile_object.open(fname, 'w');
-    save(std::make_shared<PyFileWriter>(py_ostream), a);
+    auto writer = std::make_shared<PyFileWriter>(py_ostream);
+    {
+      py::gil_scoped_release gil;
+      save(writer, a);
+    }
   }
 
   return;