[Lldb-commits] [lldb] r331229 - Protect DWARFCompileUnit::m_die_array by a new mutex

[Jan Kratochvil via lldb-commits]

Author: jankratochvil
Date: Mon Apr 30 14:37:30 2018
New Revision: 331229

URL: http://llvm.org/viewvc/llvm-project?rev=331229&view=rev
Log:
Protect DWARFCompileUnit::m_die_array by a new mutex

Multiple DW_TAG_compile_unit being indexed in a multithreaded way can request
reading of the same DW_TAG_partial_unit.

Unfortunately one cannot detect DWZ file ahead of time to disable such locking
overhead as DWARFCompileUnit::Extract does not read the first DIE which is the
only place one could find early enough if the DWARF file is using any
DW_TAG_partial_unit.

Differential revision: https://reviews.llvm.org/D40470

Modified:
    lldb/trunk/source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp
    lldb/trunk/source/Plugins/SymbolFile/DWARF/DWARFUnit.h

Modified: lldb/trunk/source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp
URL: http://llvm.org/viewvc/llvm-project/lldb/trunk/source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp?rev=331229&r1=331228&r2=331229&view=diff
==============================================================================
--- lldb/trunk/source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp (original)
+++ lldb/trunk/source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp Mon Apr 30 14:37:30 2018
@@ -41,9 +41,20 @@ DWARFUnit::~DWARFUnit() {}
 // Parses a compile unit and indexes its DIEs if it hasn't already been done.
 //----------------------------------------------------------------------
 size_t DWARFUnit::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();
+    return (cu_die_only && initial_die_array_size > 0)
+        || initial_die_array_size > 1;
+  };
+  {
+    llvm::sys::ScopedReader lock(m_extractdies_mutex);
+    if (already_parsed())
+      return 0;
+  }
+  llvm::sys::ScopedWriter lock(m_extractdies_mutex);
+  if (already_parsed())
+    return 0;
 
   static Timer::Category func_cat(LLVM_PRETTY_FUNCTION);
   Timer scoped_timer(
@@ -304,6 +315,8 @@ void DWARFUnit::SetAddrBase(dw_addr_t ad
 
 void DWARFUnit::ClearDIEs(bool keep_compile_unit_die) {
   if (m_die_array.size() > 1) {
+    llvm::sys::ScopedWriter lock(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() to see

Modified: lldb/trunk/source/Plugins/SymbolFile/DWARF/DWARFUnit.h
URL: http://llvm.org/viewvc/llvm-project/lldb/trunk/source/Plugins/SymbolFile/DWARF/DWARFUnit.h?rev=331229&r1=331228&r2=331229&view=diff
==============================================================================
--- lldb/trunk/source/Plugins/SymbolFile/DWARF/DWARFUnit.h (original)
+++ lldb/trunk/source/Plugins/SymbolFile/DWARF/DWARFUnit.h Mon Apr 30 14:37:30 2018
@@ -13,6 +13,7 @@
 #include "DWARFDIE.h"
 #include "DWARFDebugInfoEntry.h"
 #include "lldb/lldb-enumerations.h"
+#include "llvm/Support/RWMutex.h"
 
 class DWARFUnit;
 class DWARFCompileUnit;
@@ -160,6 +161,7 @@ protected:
   // If this is a dwo compile unit this is the offset of the base compile unit
   // in the main object file
   dw_offset_t m_base_obj_offset = DW_INVALID_OFFSET;
+  llvm::sys::RWMutex m_extractdies_mutex;
 
   static void
   IndexPrivate(DWARFUnit *dwarf_cu, const lldb::LanguageType cu_language,