[Lldb-commits] [lldb] [lldb][progress] Add progress manager class (PR #81319)

[Greg Clayton via lldb-commits]

================
@@ -66,3 +66,47 @@ void Progress::ReportProgress() {
                              m_debugger_id);
   }
 }
+
+void ProgressManager::Initialize() {
+  lldbassert(!InstanceImpl() && "A progress report manager already exists.");
+  InstanceImpl().emplace();
+}
+
+void ProgressManager::Terminate() {
+  lldbassert(InstanceImpl() &&
+             "A progress report manager has already been terminated.");
+  InstanceImpl().reset();
+}
+
+std::optional<ProgressManager> &ProgressManager::InstanceImpl() {
+  static std::optional<ProgressManager> g_progress_manager;
+  return g_progress_manager;
+}
+
+ProgressManager::ProgressManager() : m_progress_map() {}
+
+ProgressManager::~ProgressManager() {}
+
+ProgressManager &ProgressManager::Instance() { return *InstanceImpl(); }
----------------
clayborg wrote:

If we want to use a static variable in `std::optional<ProgressManager> &ProgressManager::InstanceImpl()`, then we need to return a `std::optional<ProgressManager>` here and people need to check it and not use it if the optional isn't valid. If we always want to return a "ProgressManager &" here, then we need `InstanceImpl()` to look like:
```
ProgressManager &ProgressManager::InstanceImpl() {
  static std::once g_once_flag;
  static ProgressManager  *g_progress_manager = nullptr;
  std::call_once(std::call_once(g_once_flag, {
    // NOTE: known leak to avoid global destructor chain issues.
    g_progress_manager = new ProgressManager(); 
  });
  return *g_progress_manager;
}
```
And then we don't need `ProgressManager::Initialize()` or `ProgressManager::Terminate()`.

The problem is when the process exits, the main thread exists and calls the C++ global destructor chain and if any threads are still running and call any of these functions that require the global instance of `ProgressManager`, it can crash the process.


https://github.com/llvm/llvm-project/pull/81319