[lldb] Flush the global thread pool in Debugger::Terminate

[JDevlieghere]

Summary

Use the Initialize/Terminate pattern for the global thread pool to make sure it gets flushed during teardown.

[JDevlieghere]

• Create the thread pool before the plugin callback

[JDevlieghere]

@labath Ping in case it got pushed down your review queue.

[jasonmolenda]

This looks good to me.

lldb/source/Core/Debugger.cpp

 
 #pragma mark Static Functions
 
 typedef std::vector<DebuggerSP> DebuggerList;
 static std::recursive_mutex *g_debugger_list_mutex_ptr =
     nullptr; // NOTE: intentional leak to avoid issues with C++ destructor chain
 static DebuggerList *g_debugger_list_ptr =
     nullptr; // NOTE: intentional leak to avoid issues with C++ destructor chain
+static llvm::ThreadPool *g_thread_pool = nullptr;
 
 static constexpr OptionEnumValueElement g_show_disassembly_enum_values[] = {
     {
         Debugger::eStopDisassemblyTypeNever,
         "never",
         "Never show disassembly when displaying a stop context.",
     },
     {

 //}
 //
 
 void Debugger::Initialize(LoadPluginCallbackType load_plugin_callback) {
   assert(g_debugger_list_ptr == nullptr &&
          "Debugger::Initialize called more than once!");
   g_debugger_list_mutex_ptr = new std::recursive_mutex();
   g_debugger_list_ptr = new DebuggerList();
+  g_thread_pool = new llvm::ThreadPool(llvm::optimal_concurrency());
   g_load_plugin_callback = load_plugin_callback;
 }
 
 void Debugger::Terminate() {
   assert(g_debugger_list_ptr &&
          "Debugger::Terminate called without a matching Debugger::Initialize!");
 
+  if (g_thread_pool) {
+    // The destructor will wait for all the threads to complete.
+    delete g_thread_pool;
+  }
+
   if (g_debugger_list_ptr && g_debugger_list_mutex_ptr) {
     // Clear our global list of debugger objects
     {
       std::lock_guard<std::recursive_mutex> guard(*g_debugger_list_mutex_ptr);
       for (const auto &debugger : *g_debugger_list_ptr)
         debugger->Clear();
       g_debugger_list_ptr->clear();
     }
Status Debugger::RunREPL(LanguageType language, const char *repl_options) {
 
   repl_sp->SetCompilerOptions(repl_options);
   repl_sp->RunLoop();
 
   return err;
 }
 
 llvm::ThreadPool &Debugger::GetThreadPool() {
-  // NOTE: intentional leak to avoid issues with C++ destructor chain
-  static llvm::ThreadPool *g_thread_pool = nullptr;
-  static llvm::once_flag g_once_flag;
-  llvm::call_once(g_once_flag, []() {
-    g_thread_pool = new llvm::ThreadPool(llvm::optimal_concurrency());
-  });
+  assert(g_thread_pool &&
+         "Debugger::GetThreadPool called before Debugger::Initialize");
   return *g_thread_pool;
 }