[Lldb-commits] [PATCH] D35083: [TypeSystem] Guard the global `ASTSourceMap` with a mutex

Sean Callanan via Phabricator via lldb-commits lldb-commits at lists.llvm.org
Tue Jul 11 13:30:05 PDT 2017

spyffe updated this revision to Diff 106087.
spyffe added a comment.

Upon reflection, it's not worth coming up with a new pattern if

- that pattern does not considerably reduce the incidence of bugs in the source file I'm applying it in (and indeed that seems quite unlikely), and
- that pattern is unlikely to be adopted elsewhere.

I'm going to simply pass in a `std::unique_lock` and swap into that.  This has the pleasant side effect of guarding the `g_totalSizeOfMetadata` variable against at least some overrides, although to be honest I'd accept a separate patch that removes this variable.




Index: source/Symbol/ClangExternalASTSourceCommon.cpp
--- source/Symbol/ClangExternalASTSourceCommon.cpp
+++ source/Symbol/ClangExternalASTSourceCommon.cpp
@@ -10,23 +10,29 @@
 #include "lldb/Symbol/ClangExternalASTSourceCommon.h"
 #include "lldb/Utility/Stream.h"
+#include <mutex>
 using namespace lldb_private;
 uint64_t g_TotalSizeOfMetadata = 0;
 typedef llvm::DenseMap<clang::ExternalASTSource *,
                        ClangExternalASTSourceCommon *>
-static ASTSourceMap &GetSourceMap() {
+static ASTSourceMap &GetSourceMap(std::unique_lock<std::mutex> &guard) {
   // Intentionally leaked to avoid problems with global destructors.
   static ASTSourceMap *s_source_map = new ASTSourceMap;
+  static std::mutex s_mutex;
+  std::unique_lock<std::mutex> locked_guard(s_mutex);
+  guard.swap(locked_guard);
   return *s_source_map;
 ClangExternalASTSourceCommon *
 ClangExternalASTSourceCommon::Lookup(clang::ExternalASTSource *source) {
-  ASTSourceMap &source_map = GetSourceMap();
+  std::unique_lock<std::mutex> guard;
+  ASTSourceMap &source_map = GetSourceMap(guard);
   ASTSourceMap::iterator iter = source_map.find(source);
@@ -40,11 +46,13 @@
     : clang::ExternalASTSource() {
   g_TotalSizeOfMetadata += m_metadata.size();
-  GetSourceMap()[this] = this;
+  std::unique_lock<std::mutex> guard;
+  GetSourceMap(guard)[this] = this;
 ClangExternalASTSourceCommon::~ClangExternalASTSourceCommon() {
-  GetSourceMap().erase(this);
+  std::unique_lock<std::mutex> guard;
+  GetSourceMap(guard).erase(this);
   g_TotalSizeOfMetadata -= m_metadata.size();

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