[Build] fix file_data_loader.cpp build issues for windows

Two build issues have been addressed in this pull request:

1. Avoid closing when fd_ is -1, as this would cause a crash on Windows.
2. Introduce separate headers for Windows and Unix, enabling Windows builds
   to utilize a distinct header and implement pread.

For pytorch#4661

CMakeLists.txt

@@ -785,6 +785,11 @@ if(EXECUTORCH_BUILD_EXECUTOR_RUNNER)
   endif()
 
   add_executable(executor_runner ${_executor_runner__srcs})
+  if(WIN32)
+    target_include_directories(executor_runner PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/extension/data_loader/Windows)
+  else()
+    target_include_directories(executor_runner PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/extension/data_loader/Unix)
+  endif()
   if(CMAKE_BUILD_TYPE STREQUAL "Release")
     if(APPLE)
       target_link_options(executor_runner PRIVATE "LINKER:-dead_strip")

extension/data_loader/CMakeLists.txt

@@ -20,6 +20,11 @@ list(TRANSFORM _extension_data_loader__srcs PREPEND "${EXECUTORCH_ROOT}/")
 add_library(extension_data_loader ${_extension_data_loader__srcs})
 target_link_libraries(extension_data_loader executorch)
 target_include_directories(extension_data_loader PUBLIC ${EXECUTORCH_ROOT}/..)
+if(WIN32)
+  target_include_directories(extension_data_loader PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/Windows)
+else()
+  target_include_directories(extension_data_loader PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/Unix)
+endif()
 target_compile_options(extension_data_loader PUBLIC ${_common_compile_options})
 
 # Install libraries

extension/data_loader/Unix/file.h

@@ -0,0 +1,11 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#pragma once
+
+#include <unistd.h>

extension/data_loader/Windows/file.h

@@ -0,0 +1,53 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#pragma once
+
+#include <executorch/runtime/platform/compiler.h> // For ssize_t.
+#include <io.h>
+
+#include <windows.h>
+
+inline ssize_t pread(int __fd, void* __buf, size_t __nbytes, size_t __offset) {
+  OVERLAPPED overlapped; /* The offset for ReadFile. */
+  memset(&overlapped, 0, sizeof(overlapped));
+  overlapped.Offset = __offset;
+  overlapped.OffsetHigh = __offset >> 32;
+
+  BOOL result; /* The result of ReadFile. */
+  DWORD bytes_read; /* The number of bytes read. */
+  HANDLE file = (HANDLE)_get_osfhandle(__fd);
+
+  result = ReadFile(file, __buf, __nbytes, &bytes_read, &overlapped);
+  DWORD error = GetLastError();
+  if (!result) {
+    if (error == ERROR_IO_PENDING) {
+      result = GetOverlappedResult(file, &overlapped, &bytes_read, TRUE);
+      if (!result) {
+        error = GetLastError();
+      }
+    }
+  }
+  if (!result) {
+    // Translate error into errno.
+    switch (error) {
+      case ERROR_HANDLE_EOF:
+        errno = 0;
+        break;
+      default:
+        errno = EIO;
+        break;
+    }
+    return -1;
+  }
+  return bytes_read;
+}
+
+// To avoid conflicts with std::numeric_limits<int32_t>::max() in
+// file_data_loader.cpp.
+#undef max

extension/data_loader/file_data_loader.cpp

@@ -7,6 +7,7 @@
  */
 
 #include <executorch/extension/data_loader/file_data_loader.h>
+#include <file.h>
 
 #include <algorithm>
 #include <cerrno>
@@ -17,7 +18,6 @@
 #include <fcntl.h>
 #include <sys/stat.h>
 #include <sys/types.h>
-#include <unistd.h>
 
 #include <executorch/runtime/core/error.h>
 #include <executorch/runtime/core/result.h>
@@ -69,8 +69,10 @@ FileDataLoader::~FileDataLoader() {
   // file_name_ can be nullptr if this instance was moved from, but freeing a
   // null pointer is safe.
   std::free(const_cast<char*>(file_name_));
-  // fd_ can be -1 if this instance was moved from, but closing a negative fd is
-  // safe (though it will return an error).
+  // fd_ can be -1 if this instance was moved from.
+  if (fd_ == -1) {
+    return;
+  }
   ::close(fd_);
 }