[NFC][SYCL] Move platform::khr_get_default_context impl to platform_impl.cpp (#19157)

Noticed this code as part of the ongoing refactoring to prefer raw
ptrs/refs for SYCL RT `*_impl` objects. The usage of this API in
`queue_impl` doesn't need to go through user-visible SYCL objects, so
move the implementation and use the internal interfrace in `queue_impl`
and delegate `platform::khr_get_default_context` to `platform_impl`.

Author: aelovikov-intel

sycl/source/detail/platform_impl.cpp

@@ -71,6 +71,23 @@ platform_impl::getPlatformFromUrDevice(ur_device_handle_t UrDevice,
   return getOrMakePlatformImpl(Plt, Adapter);
 }
 
+context_impl &platform_impl::khr_get_default_context() {
+  GlobalHandler &GH = GlobalHandler::instance();
+  // Keeping the default context for platforms in the global cache to avoid
+  // shared_ptr based circular dependency between platform and context classes
+  std::unordered_map<platform_impl *, std::shared_ptr<context_impl>>
+      &PlatformToDefaultContextCache = GH.getPlatformToDefaultContextCache();
+
+  std::lock_guard<std::mutex> Lock{GH.getPlatformToDefaultContextCacheMutex()};
+
+  auto It = PlatformToDefaultContextCache.find(this);
+  if (PlatformToDefaultContextCache.end() == It)
+    std::tie(It, std::ignore) = PlatformToDefaultContextCache.insert(
+        {this, detail::getSyclObjImpl(context{get_devices()})});
+
+  return *It->second;
+}
+
 static bool IsBannedPlatform(platform Platform) {
   // The NVIDIA OpenCL platform is currently not compatible with DPC++
   // since it is only 1.2 but gets selected by default in many systems

sycl/source/detail/platform_impl.hpp

@@ -203,6 +203,8 @@ class platform_impl : public std::enable_shared_from_this<platform_impl> {
   static platform_impl &getPlatformFromUrDevice(ur_device_handle_t UrDevice,
                                                 const AdapterPtr &Adapter);
 
+  context_impl &khr_get_default_context();
+
   // when getting sub-devices for ONEAPI_DEVICE_SELECTOR we may temporarily
   // ensure every device is a root one.
   bool MAlwaysRootDevice = false;

sycl/source/detail/queue_impl.hpp

@@ -83,17 +83,17 @@ class queue_impl : public std::enable_shared_from_this<queue_impl> {
 public:
   // \return a default context for the platform if it includes the device
   // passed and default contexts are enabled, a new context otherwise.
-  static ContextImplPtr getDefaultOrNew(device_impl &Device) {
-    if (!SYCLConfig<SYCL_ENABLE_DEFAULT_CONTEXTS>::get())
-      return detail::getSyclObjImpl(
-          context{createSyclObjFromImpl<device>(Device), {}, {}});
-
-    ContextImplPtr DefaultContext =
-        detail::getSyclObjImpl(Device.get_platform().khr_get_default_context());
-    if (DefaultContext->isDeviceValid(Device))
-      return DefaultContext;
-    return detail::getSyclObjImpl(
-        context{createSyclObjFromImpl<device>(Device), {}, {}});
+  static std::shared_ptr<context_impl> getDefaultOrNew(device_impl &Device) {
+    if (SYCLConfig<SYCL_ENABLE_DEFAULT_CONTEXTS>::get()) {
+      context_impl &CtxImpl =
+          Device.getPlatformImpl().khr_get_default_context();
+      if (CtxImpl.isDeviceValid(Device))
+        return CtxImpl.shared_from_this();
+    }
+
+    return context_impl::create(
+        std::vector<device>{createSyclObjFromImpl<device>(Device)},
+        async_handler{}, property_list{});
   }
   /// Constructs a SYCL queue from a device using an async_handler and
   /// property_list provided.

sycl/source/platform.cpp

@@ -8,6 +8,7 @@
 
 #include <detail/backend_impl.hpp>
 #include <detail/config.hpp>
+#include <detail/context_impl.hpp>
 #include <detail/global_handler.hpp>
 #include <detail/platform_impl.hpp>
 #include <detail/ur.hpp>
@@ -89,22 +90,8 @@ platform::get_backend_info() const {
 #undef __SYCL_PARAM_TRAITS_SPEC
 
 context platform::khr_get_default_context() const {
-  // Keeping the default context for platforms in the global cache to avoid
-  // shared_ptr based circular dependency between platform and context classes
-  std::unordered_map<detail::platform_impl *, detail::ContextImplPtr>
-      &PlatformToDefaultContextCache =
-          detail::GlobalHandler::instance().getPlatformToDefaultContextCache();
-
-  std::lock_guard<std::mutex> Lock{
-      detail::GlobalHandler::instance()
-          .getPlatformToDefaultContextCacheMutex()};
-
-  auto It = PlatformToDefaultContextCache.find(impl.get());
-  if (PlatformToDefaultContextCache.end() == It)
-    std::tie(It, std::ignore) = PlatformToDefaultContextCache.insert(
-        {impl.get(), detail::getSyclObjImpl(context{get_devices()})});
-
-  return detail::createSyclObjFromImpl<context>(It->second);
+  return detail::createSyclObjFromImpl<context>(
+      impl->khr_get_default_context());
 }
 
 context platform::ext_oneapi_get_default_context() const {