allow single thread deployment (rime#673)

CMakeLists.txt

@@ -25,6 +25,7 @@ option(BOOST_USE_SIGNALS2 "Boost use signals2 instead of signals" ON)
 option(ENABLE_ASAN "Enable Address Sanitizer (Unix Only)" OFF)
 option(INSTALL_PRIVATE_HEADERS "Install private headers (usually needed for externally built Rime plugins)" OFF)
 option(ENABLE_EXTERNAL_PLUGINS "Enable loading of externally built Rime plugins (from directory set by RIME_PLUGINS_DIR variable)" OFF)
+option(ENABLE_THREADING "Enable threading for deployer" ON)
 
 set(RIME_DATA_DIR "${CMAKE_INSTALL_FULL_DATADIR}/rime-data" CACHE STRING "Target directory for Rime data")
 set(RIME_PLUGINS_DIR "${CMAKE_INSTALL_FULL_LIBDIR}/rime-plugins" CACHE STRING "Target directory for externally built Rime plugins")
@@ -97,6 +98,10 @@ endif()
 
 find_package(Threads)
 
+if(NOT ENABLE_THREADING)
+  add_definitions(-DRIME_NO_THREADING)
+endif()
+
 if(BUILD_TEST)
   find_package(GTest REQUIRED)
   if(GTEST_FOUND)

src/rime/deployer.cc

@@ -106,10 +106,15 @@ bool Deployer::StartWork(bool maintenance_mode) {
   if (pending_tasks_.empty()) {
     return false;
   }
+#ifdef RIME_NO_THREADING
+  LOG(INFO) << "running " << pending_tasks_.size() << " tasks in main thread.";
+  return Run();
+#else
   LOG(INFO) << "starting work thread for " << pending_tasks_.size()
             << " tasks.";
   work_ = std::async(std::launch::async, [this] { Run(); });
   return work_.valid();
+#endif
 }
 
 bool Deployer::StartMaintenance() {