Running gRPC Server independently (#158)

The loading/unloading behavior of the Vulkan/OpenXR Dive layer library varies significantly across Android applications. For example for Vulkan apps it loads - unloads - reloads the library during execution. For an Unity-based OpenXR app that creates two instances, the behavior is the same. The gRPC Server starts when the library loads for the first time. Then, a function prevents the library from being unloaded. This keeps both the library and server loaded exactly once, even if apps try to reload or close them. In this way, the Server lives for the entire lifecycle of the app.
google · Jan 30, 2025 · b4f8b82 · b4f8b82
1 parent 9fe68b2
commit b4f8b82
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Showing 6 changed files with 74 additions and 22 deletions.
diff --git a/capture_service/server.cc b/capture_service/server.cc
@@ -16,7 +16,8 @@ limitations under the License.
 
 #include "server.h"
 
-int main(int argc, char **argv) {
-    Dive::server_main();
+int main(int argc, char **argv)
+{
+    Dive::ServerMain();
     return 0;
 }
diff --git a/capture_service/server.h b/capture_service/server.h
@@ -18,5 +18,6 @@ limitations under the License.
 
 namespace Dive
 {
-int server_main();
-}
+int  ServerMain();
+void StopServer();
+}  // namespace Dive
diff --git a/capture_service/service.cc b/capture_service/service.cc
@@ -132,8 +132,26 @@ grpc::Status DiveServiceImpl::DownloadFile(grpc::ServerContext             *cont
     return grpc::Status::OK;
 }
 
+std::unique_ptr<grpc::Server> &GetServer()
+{
+    static std::unique_ptr<grpc::Server> server = nullptr;
+    return server;
+}
+
+void StopServer()
+{
+    auto &server = GetServer();
+    if (server)
+    {
+        LOGI("StopServer at service.cc");
+        server->Shutdown();
+        server = nullptr;
+    }
+}
+
 void RunServer(uint16_t port)
 {
+    LOGI("port is %d\n", port);
     std::string     server_address = absl::StrFormat("0.0.0.0:%d", port);
     DiveServiceImpl service;
 
@@ -142,12 +160,13 @@ void RunServer(uint16_t port)
     builder.AddListeningPort(server_address, grpc::InsecureServerCredentials());
 
     builder.RegisterService(&service);
-    std::unique_ptr<grpc::Server> server(builder.BuildAndStart());
+    auto &server = GetServer();
+    server = builder.BuildAndStart();
     LOGI("Server listening on %s", server_address.c_str());
     server->Wait();
 }
 
-int server_main()
+int ServerMain()
 {
     RunServer(absl::GetFlag(FLAGS_port));
     return 0;

diff --git a/layer/layer_common.cc b/layer/layer_common.cc
@@ -14,6 +14,12 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
+#ifdef _WIN32
+#    include <windows.h>
+#else
+#    include <dlfcn.h>
+#endif
+
 #include "layer_common.h"
 
 #include <cstdio>
@@ -58,14 +64,15 @@ ServerRunner::ServerRunner()
     LOGI("libwrap loaded: %d", is_libwrap_loaded);
     if (is_libwrap_loaded)
     {
-        server_thread = std::thread(Dive::server_main);
+        server_thread = std::thread(Dive::ServerMain);
     }
 }
 
 ServerRunner::~ServerRunner()
 {
     if (is_libwrap_loaded && server_thread.joinable())
     {
+        Dive::StopServer();
         LOGI("Wait for server thread to join");
         server_thread.join();
     }
@@ -77,4 +84,41 @@ ServerRunner &GetServerRunner()
     return runner;
 }
 
-}  // namespace DiveLayer
+}  // namespace DiveLayer
+
+void PreventLibraryUnload()
+{
+#ifdef _WIN32
+    HMODULE module = nullptr;
+    GetModuleHandleEx(GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS | GET_MODULE_HANDLE_EX_FLAG_PIN,
+                      reinterpret_cast<LPCSTR>(&PreventLibraryUnload),
+                      &module);
+#else
+    Dl_info info;
+    if (dladdr(reinterpret_cast<void *>(&PreventLibraryUnload), &info))
+    {
+        dlopen(info.dli_fname, RTLD_NOW | RTLD_NOLOAD | RTLD_LOCAL | RTLD_NODELETE);
+    }
+#endif
+}
+
+#ifdef _WIN32
+BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved)
+{
+    if (fdwReason == DLL_PROCESS_ATTACH)
+    {
+        [[maybe_unused]] auto &server = DiveLayer::GetServerRunner();
+        PreventLibraryUnload();
+    }
+    return TRUE;
+}
+#else
+extern "C"
+{
+    __attribute__((constructor)) void InitializeLibrary()
+    {
+        [[maybe_unused]] auto &server = DiveLayer::GetServerRunner();
+        PreventLibraryUnload();
+    }
+}
+#endif
diff --git a/layer/openxr_layer.cc b/layer/openxr_layer.cc
@@ -56,12 +56,6 @@ struct XrSessionData
 {
     XrSession                session;
     XrGeneratedDispatchTable dispatch_table;
-    ServerRunner            &server;
-
-    XrSessionData() :
-        server(GetServerRunner())
-    {
-    }
 };
 
 static thread_local XrInstanceData *last_used_xr_instance_data = nullptr;
@@ -190,8 +184,7 @@ XRAPI_ATTR XrResult XRAPI_CALL ApiDiveLayerXrDestroyInstance(XrInstance instance
 
     LOGD("ApiDiveLayerXrDestroyInstance\n");
     XrResult result = XR_SUCCESS;
-
-    auto sess_data = GetXrInstanceLayerData(DataKey(instance));
+    auto     sess_data = GetXrInstanceLayerData(DataKey(instance));
     if (sess_data)
     {
         result = sess_data->dispatch_table.DestroyInstance(instance);

diff --git a/layer/vk_layer_base.cc b/layer/vk_layer_base.cc
@@ -43,12 +43,6 @@ struct InstanceData
 {
     VkInstance            instance;
     InstanceDispatchTable dispatch_table;
-    ServerRunner         &server;
-
-    InstanceData() :
-        server(GetServerRunner())
-    {
-    }
 };
 
 struct DeviceData