[Lldb-commits] [lldb] SBDebugger: Add new APIs `AddDestroyCallback` and `RemoveDestroyCallback` (PR #89868)

[via lldb-commits]

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@@ -743,9 +743,28 @@ DebuggerSP Debugger::CreateInstance(lldb::LogOutputCallback log_callback,
 }
 
 void Debugger::HandleDestroyCallback() {
-  if (m_destroy_callback) {
-    m_destroy_callback(GetID(), m_destroy_callback_baton);
-    m_destroy_callback = nullptr;
+  std::lock_guard<std::recursive_mutex> guard(m_destroy_callback_mutex);
+  const lldb::user_id_t user_id = GetID();
+  // This loop handles the case where callbacks are added/removed by existing
+  // callbacks during the loop, as the following:
+  // - Added callbacks will always be invoked.
+  // - Removed callbacks will never be invoked. That is *unless* the loop
+  //   happens to invoke the said callbacks first, before they get removed.
+  //   In this case, the callbacks gets invoked, and the removal return false.
+  //
+  // In the removal case, because the order of the container is random, it's
+  // wise to not depend on the order and instead implement logic inside the
+  // callbacks to decide if their work should be skipped.
+  while (m_destroy_callback_and_baton.size()) {
+    auto iter = m_destroy_callback_and_baton.begin();
+    const lldb::destroy_callback_token_t &token = iter->first;
+    const lldb_private::DebuggerDestroyCallback &callback = iter->second.first;
+    void *const &baton = iter->second.second;
+    callback(user_id, baton);
+    // Using `token` to erase, because elements may have been added/removed, and
+    // that will cause error "invalid iterator access!" if `iter` is used
+    // instead.
+    m_destroy_callback_and_baton.erase(token);
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jeffreytan81 wrote:

Any reason we remove after calling the callback?

https://github.com/llvm/llvm-project/pull/89868