Only create thread if used

Author: jhuber6

offload/plugins-nextgen/common/include/RPC.h

@@ -44,6 +44,9 @@ struct RPCServerTy {
   /// Deinitialize the associated memory and resources.
   llvm::Error shutDown();
 
+  /// Initialize the worker thread.
+  llvm::Error startThread();
+
   /// Check if this device image is using an RPC server. This checks for the
   /// precense of an externally visible symbol in the device image that will
   /// be present whenever RPC code is called.
@@ -85,7 +88,9 @@ struct RPCServerTy {
     llvm::ArrayRef<std::atomic<uintptr_t>> Handles;
 
     /// Initialize the worker thread to run in the background.
-    ServerThread(std::atomic<uintptr_t> Handles[], size_t Length);
+    ServerThread(std::atomic<uintptr_t> Handles[], size_t Length)
+        : Running(true), NumUsers(0), CV(), Mutex(), Handles(Handles, Length) {}
+
     ~ServerThread() { assert(!Running && "Thread not shut down explicitly\n"); }
 
     /// Notify the worker thread that there is a user that needs it.
@@ -105,6 +110,9 @@ struct RPCServerTy {
     /// Destroy the worker thread and wait.
     void shutDown();
 
+    /// Initialize the worker thread.
+    void startThread();
+
     /// Run the server thread to continuously check the RPC interface for work
     /// to be done for the device.
     void run();

offload/plugins-nextgen/common/src/PluginInterface.cpp

@@ -1051,6 +1051,9 @@ Error GenericDeviceTy::setupRPCServer(GenericPluginTy &Plugin,
   if (auto Err = Server.initDevice(*this, Plugin.getGlobalHandler(), Image))
     return Err;
 
+  if (auto Err = Server.startThread())
+    return Err;
+
   RPCServer = &Server;
   DP("Running an RPC server on device %d\n", getDeviceId());
   return Plugin::success();

offload/plugins-nextgen/common/src/RPC.cpp

@@ -21,6 +21,12 @@ using namespace llvm;
 using namespace omp;
 using namespace target;
 
+void RPCServerTy::ServerThread::startThread() {
+#ifdef LIBOMPTARGET_RPC_SUPPORT
+  Worker = std::thread([this]() { run(); });
+#endif
+}
+
 void RPCServerTy::ServerThread::shutDown() {
 #ifdef LIBOMPTARGET_RPC_SUPPORT
   {
@@ -60,19 +66,18 @@ void RPCServerTy::ServerThread::run() {
 #endif
 }
 
-RPCServerTy::ServerThread::ServerThread(std::atomic<uintptr_t> Handles[],
-                                        size_t Length)
-    : Running(true), NumUsers(0), CV(), Mutex(), Handles(Handles, Length) {
-#ifdef LIBOMPTARGET_RPC_SUPPORT
-  Worker = std::thread([this]() { run(); });
-#endif
-}
-
 RPCServerTy::RPCServerTy(plugin::GenericPluginTy &Plugin)
     : Handles(
           std::make_unique<std::atomic<uintptr_t>[]>(Plugin.getNumDevices())),
       Thread(new ServerThread(Handles.get(), Plugin.getNumDevices())) {}
 
+llvm::Error RPCServerTy::startThread() {
+#ifdef LIBOMPTARGET_RPC_SUPPORT
+  Thread->startThread();
+#endif
+  return Error::success();
+}
+
 llvm::Error RPCServerTy::shutDown() {
 #ifdef LIBOMPTARGET_RPC_SUPPORT
   Thread->shutDown();