[Lldb-commits] [PATCH] D29288: Switch std::call_once to llvm::call_once

Pavel Labath via Phabricator via lldb-commits lldb-commits at lists.llvm.org
Sat Feb 4 17:26:51 PST 2017

labath added inline comments.

Comment at: include/lldb/Core/Debugger.h:379
   lldb::ListenerSP m_forward_listener_sp;
-  std::once_flag m_clear_once;
+  llvm::once_flag m_clear_once;
The code in llvm says you should only ever use the LLVM_DEFINE_ONCE_FLAG to declare flags. I am guessing it's because it forces the `static` keyword into the declaration, which in turn guarantees your object will be zero-initialized by the linker. If you declare the flag as a local variable like this, it will be initialized to a random value, and you will have a fun time debugging issues in the future (it will only affect netbsd, as std::call_once platforms will still be correctly initialized).

Comment at: source/Core/ModuleList.cpp:648
 static ModuleList &GetSharedModuleList() {
   static ModuleList *g_shared_module_list = nullptr;
+  LLVM_DEFINE_ONCE_FLAG(g_once_flag);
This could be simplified to:
```static ModuleList *g_shared_module_list = new ModuleList();```

It's only written this way because MSVC at one point did not support thread-safe statics.



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