[libclang] Implement ConcurrencyCheck using a recursive mutex to allow re-entrancy in the same thread.

The checks are performed only in DEBUG, it becomes no-op in release mode.

llvm-svn: 141582

clang/include/clang/Frontend/ASTUnit.h

@@ -151,16 +151,6 @@ private:
   /// destroyed.
   SmallVector<llvm::sys::Path, 4> TemporaryFiles;
   
-  /// \brief Simple hack to allow us to assert that ASTUnit is not being
-  /// used concurrently, which is not supported.
-  ///
-  /// Clients should create instances of the ConcurrencyCheck class whenever
-  /// using the ASTUnit in a way that isn't intended to be concurrent, which is
-  /// just about any usage.
-  unsigned int ConcurrencyCheckValue;
-  static const unsigned int CheckLocked = 28573289;
-  static const unsigned int CheckUnlocked = 9803453;
-
   /// \brief Counter that determines when we want to try building a
   /// precompiled preamble.
   ///
@@ -406,21 +396,37 @@ private:
                                                         unsigned MaxLines = 0);
   void RealizeTopLevelDeclsFromPreamble();
   
+  /// \brief Allows us to assert that ASTUnit is not being used concurrently,
+  /// which is not supported.
+  ///
+  /// Clients should create instances of the ConcurrencyCheck class whenever
+  /// using the ASTUnit in a way that isn't intended to be concurrent, which is
+  /// just about any usage.
+  /// Becomes a noop in release mode; only useful for debug mode checking.
+  class ConcurrencyState {
+    void *Mutex; // a llvm::sys::MutexImpl in debug;
+
+  public:
+    ConcurrencyState();
+    ~ConcurrencyState();
+
+    void start();
+    void finish();
+  };
+  ConcurrencyState ConcurrencyCheckValue;
+
 public:
   class ConcurrencyCheck {
-    volatile ASTUnit &Self;
+    ASTUnit &Self;
     
   public:
     explicit ConcurrencyCheck(ASTUnit &Self)
       : Self(Self) 
     { 
-      assert(Self.ConcurrencyCheckValue == CheckUnlocked && 
-             "Concurrent access to ASTUnit!");
-      Self.ConcurrencyCheckValue = CheckLocked;
+      Self.ConcurrencyCheckValue.start();
     }
-    
     ~ConcurrencyCheck() {
-      Self.ConcurrencyCheckValue = CheckUnlocked;
+      Self.ConcurrencyCheckValue.finish();
     }
   };
   friend class ConcurrencyCheck;

clang/lib/Frontend/ASTUnit.cpp

@@ -45,6 +45,7 @@
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Support/Timer.h"
 #include "llvm/Support/FileSystem.h"
+#include "llvm/Support/Mutex.h"
 #include "llvm/Support/CrashRecoveryContext.h"
 #include <cstdlib>
 #include <cstdio>
@@ -99,7 +100,6 @@ ASTUnit::ASTUnit(bool _MainFileIsAST)
     TUKind(TU_Complete), WantTiming(getenv("LIBCLANG_TIMING")),
     OwnsRemappedFileBuffers(true),
     NumStoredDiagnosticsFromDriver(0),
-    ConcurrencyCheckValue(CheckUnlocked), 
     PreambleRebuildCounter(0), SavedMainFileBuffer(0), PreambleBuffer(0),
     ShouldCacheCodeCompletionResults(false),
     NestedMacroExpansions(true),
@@ -114,7 +114,6 @@ ASTUnit::ASTUnit(bool _MainFileIsAST)
 }
 
 ASTUnit::~ASTUnit() {
-  ConcurrencyCheckValue = CheckLocked;
   CleanTemporaryFiles();
   if (!PreambleFile.empty())
     llvm::sys::Path(PreambleFile).eraseFromDisk();
@@ -2414,3 +2413,30 @@ void ASTUnit::PreambleData::countLines() const {
   if (Buffer.back() != '\n')
     ++NumLines;
 }
+
+#ifndef NDEBUG
+ASTUnit::ConcurrencyState::ConcurrencyState() {
+  Mutex = new llvm::sys::MutexImpl(/*recursive=*/true);
+}
+
+ASTUnit::ConcurrencyState::~ConcurrencyState() {
+  delete static_cast<llvm::sys::MutexImpl *>(Mutex);
+}
+
+void ASTUnit::ConcurrencyState::start() {
+  bool acquired = static_cast<llvm::sys::MutexImpl *>(Mutex)->tryacquire();
+  assert(acquired && "Concurrent access to ASTUnit!");
+}
+
+void ASTUnit::ConcurrencyState::finish() {
+  static_cast<llvm::sys::MutexImpl *>(Mutex)->release();
+}
+
+#else // NDEBUG
+
+ASTUnit::ConcurrencyState::ConcurrencyState() {}
+ASTUnit::ConcurrencyState::~ConcurrencyState() {}
+void ASTUnit::ConcurrencyState::start() {}
+void ASTUnit::ConcurrencyState::finish() {}
+
+#endif