[SYCL] Balance device reference counter (#6708)

While it's not strictly required to release(decrement reference
counters) of handles of root devices it might be convenient for
plugins to have the same behavior as for other handles.

Author: romanovvlad

sycl/source/detail/platform_impl.cpp

@@ -505,6 +505,10 @@ platform_impl::get_devices(info::device_type DeviceType) const {
       pi::cast<RT::PiDeviceType>(DeviceType), // CP info::device_type::all
       NumDevices, PiDevices.data(), nullptr);
 
+  // Some elements of PiDevices vector might be filtered out, so make a copy of
+  // handles to do a cleanup later
+  std::vector<RT::PiDevice> PiDevicesToCleanUp = PiDevices;
+
   // Filter out devices that are not present in the SYCL_DEVICE_ALLOWLIST
   if (SYCLConfig<SYCL_DEVICE_ALLOWLIST>::get())
     applyAllowList(PiDevices, MPlatform, Plugin);
@@ -537,6 +541,11 @@ platform_impl::get_devices(info::device_type DeviceType) const {
             PlatformImpl->getOrMakeDeviceImpl(PiDevice, PlatformImpl));
       });
 
+  // The reference counter for handles, that we used to create sycl objects, is
+  // incremented, so we need to call release here.
+  for (RT::PiDevice &PiDev : PiDevicesToCleanUp)
+    Plugin.call<PiApiKind::piDeviceRelease>(PiDev);
+
   // If we aren't using ONEAPI_DEVICE_SELECTOR, then we are done.
   // and if there are no devices so far, there won't be any need to replace them
   // with subdevices.

sycl/unittests/CMakeLists.txt

@@ -46,6 +46,6 @@ add_subdirectory(Extensions)
 add_subdirectory(windows)
 add_subdirectory(event)
 add_subdirectory(buffer)
-add_subdirectory(context)
+add_subdirectory(context_device)
 add_subdirectory(accessor)
 add_subdirectory(handler)

sycl/unittests/context/CMakeLists.txt

@@ -0,0 +1,4 @@
+add_sycl_unittest(ContextDeviceTests OBJECT
+  Context.cpp
+  DeviceRefCounter.cpp
+)

sycl/unittests/context_device/CMakeLists.txt

@@ -0,0 +1,52 @@
+//==----- DeviceRefCounter - Kernel build options processing unit test -----==//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#define SYCL2020_DISABLE_DEPRECATION_WARNINGS
+
+#include <gtest/gtest.h>
+#include <helpers/PiMock.hpp>
+#include <sycl/sycl.hpp>
+
+int DevRefCounter = 0;
+
+static pi_result redefinedDevicesGetAfter(pi_platform platform,
+                                          pi_device_type device_type,
+                                          pi_uint32 num_entries,
+                                          pi_device *devices,
+                                          pi_uint32 *num_devices) {
+  if (devices)
+    DevRefCounter += num_entries;
+  return PI_SUCCESS;
+}
+
+static pi_result redefinedDeviceRetainAfter(pi_device device) {
+  DevRefCounter++;
+  return PI_SUCCESS;
+}
+
+static pi_result redefinedDeviceReleaseAfter(pi_device device) {
+  DevRefCounter--;
+  return PI_SUCCESS;
+}
+
+TEST(DevRefCounter, DevRefCounter) {
+  {
+    sycl::unittest::PiMock Mock;
+    sycl::platform Plt = Mock.getPlatform();
+
+    Mock.redefineAfter<sycl::detail::PiApiKind::piDevicesGet>(
+        redefinedDevicesGetAfter);
+    Mock.redefineAfter<sycl::detail::PiApiKind::piDeviceRetain>(
+        redefinedDeviceRetainAfter);
+    Mock.redefineAfter<sycl::detail::PiApiKind::piDeviceRelease>(
+        redefinedDeviceReleaseAfter);
+
+    Plt.get_devices();
+  }
+  EXPECT_EQ(DevRefCounter, 0);
+}