[Lldb-commits] [PATCH] D40470: DWZ 06/11: Protect DWARFCompileUnit::m_die_array by a new mutex

[Jan Kratochvil via Phabricator via lldb-commits]

jankratochvil updated this revision to Diff 135053.
jankratochvil retitled this revision from "DWZ 07/12: Protect DWARFCompileUnit::m_die_array by a new mutex" to "DWZ 06/11: Protect DWARFCompileUnit::m_die_array by a new mutex".
jankratochvil edited the summary of this revision.

https://reviews.llvm.org/D40470

Files:
  source/Plugins/SymbolFile/DWARF/DWARFCompileUnit.cpp
  source/Plugins/SymbolFile/DWARF/DWARFCompileUnit.h


Index: source/Plugins/SymbolFile/DWARF/DWARFCompileUnit.h
===================================================================
--- source/Plugins/SymbolFile/DWARF/DWARFCompileUnit.h
+++ source/Plugins/SymbolFile/DWARF/DWARFCompileUnit.h
@@ -93,6 +93,8 @@
   void *m_user_data = nullptr;
   DWARFDebugInfoEntry::collection
       m_die_array; // The compile unit debug information entry item
+  // Prevent m_extractdies_mutex lock overhead for most cases.
+  std::atomic_size_t m_die_array_size_atomic { 0 };
   std::unique_ptr<DWARFDebugAranges> m_func_aranges_ap; // A table similar to
                                                         // the .debug_aranges
                                                         // table, but this one
@@ -116,6 +118,8 @@
   // in the main object file
   dw_offset_t m_base_obj_offset = DW_INVALID_OFFSET;
 
+  std::mutex m_extractdies_mutex;
+
   void ParseProducerInfo();
 
 private:
Index: source/Plugins/SymbolFile/DWARF/DWARFCompileUnit.cpp
===================================================================
--- source/Plugins/SymbolFile/DWARF/DWARFCompileUnit.cpp
+++ source/Plugins/SymbolFile/DWARF/DWARFCompileUnit.cpp
@@ -83,6 +83,8 @@
 
 void DWARFCompileUnit::ClearDIEs(bool keep_compile_unit_die) {
   if (m_die_array.size() > 1) {
+    std::lock_guard<std::mutex> guard(m_extractdies_mutex);
+
     // std::vectors never get any smaller when resized to a smaller size,
     // or when clear() or erase() are called, the size will report that it
     // is smaller, but the memory allocated remains intact (call capacity()
@@ -94,8 +96,11 @@
     // Save at least the compile unit DIE
     DWARFDebugInfoEntry::collection tmp_array;
     m_die_array.swap(tmp_array);
-    if (keep_compile_unit_die)
+    m_die_array_size_atomic = 0;
+    if (keep_compile_unit_die) {
       m_die_array.push_back(tmp_array.front());
+      ++m_die_array_size_atomic;
+    }
   }
 
   if (m_dwo_symbol_file)
@@ -109,9 +114,19 @@
 // done.
 //----------------------------------------------------------------------
 size_t DWARFCompileUnit::ExtractDIEsIfNeeded(bool cu_die_only) {
-  const size_t initial_die_array_size = m_die_array.size();
-  if ((cu_die_only && initial_die_array_size > 0) || initial_die_array_size > 1)
-    return 0; // Already parsed
+  size_t initial_die_array_size;
+  auto already_parsed = [cu_die_only, &initial_die_array_size, this]() -> bool {
+    initial_die_array_size = m_die_array_size_atomic;
+    return (cu_die_only && initial_die_array_size > 0)
+        || initial_die_array_size > 1;
+  };
+  if (already_parsed())
+    return 0;
+  std::lock_guard<std::mutex> guard(m_extractdies_mutex);
+  if (already_parsed())
+    return 0;
+  std::shared_ptr<void> m_die_array_finished_set(nullptr,
+      [&](void*){ m_die_array_size_atomic = m_die_array.size(); });
 
   static Timer::Category func_cat(LLVM_PRETTY_FUNCTION);
   Timer scoped_timer(


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