[Lldb-commits] [lldb] [lldb] Use Guarded in CPPLanguageRuntime (PR #219428)

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llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-lldb

Author: Raphael Isemann (Teemperor)

<details>
<summary>Changes</summary>

Use Guarded to make sure m_vtable_info_map cannot be accesses without
locking the respective lock.

---
Full diff: https://github.com/llvm/llvm-project/pull/219428.diff


4 Files Affected:

- (modified) lldb/include/lldb/Utility/Locked.h (+28) 
- (modified) lldb/source/Plugins/LanguageRuntime/CPlusPlus/CPPLanguageRuntime.cpp (+4-5) 
- (modified) lldb/source/Plugins/LanguageRuntime/CPlusPlus/CPPLanguageRuntime.h (+3-2) 
- (modified) lldb/unittests/Utility/LockedTest.cpp (+37) 


``````````diff
diff --git a/lldb/include/lldb/Utility/Locked.h b/lldb/include/lldb/Utility/Locked.h
index acd34e454a918..f5d7b1aa8e4d9 100644
--- a/lldb/include/lldb/Utility/Locked.h
+++ b/lldb/include/lldb/Utility/Locked.h
@@ -168,6 +168,34 @@ template <typename T, typename Mutex = llvm::sys::RWMutex>
 using SharedLockedUP = SharedLocked<std::unique_ptr<const T>, Mutex>;
 /// @}
 
+/// Bundles a value of type `T` with the `Mutex` that guards it.
+///
+/// This class prevents accidential use of a value without aquiring the
+/// lock and should be preferred over a member + mutex pair.
+///
+/// `Mutex` must satisfy `Lockable` when calling `Lock()` and `SharedLockable`
+/// when calling `LockShared()`.
+template <typename T, typename Mutex = llvm::sys::RWMutex> class Guarded {
+public:
+  Guarded() = default;
+  explicit Guarded(T value) : m_value(std::move(value)) {}
+
+  Guarded(const Guarded &) = delete;
+  Guarded &operator=(const Guarded &) = delete;
+
+  /// Exclusive (read/write) access to the value.
+  Locked<T *, Mutex> Lock() { return Locked<T *, Mutex>(m_mutex, &m_value); }
+
+  /// Shared (read-only) access to the value.
+  SharedLocked<const T *, Mutex> LockShared() const {
+    return SharedLocked<const T *, Mutex>(m_mutex, &m_value);
+  }
+
+private:
+  mutable Mutex m_mutex;
+  T m_value{};
+};
+
 } // namespace lldb_private
 
 #endif // LLDB_UTILITY_LOCKED_H
diff --git a/lldb/source/Plugins/LanguageRuntime/CPlusPlus/CPPLanguageRuntime.cpp b/lldb/source/Plugins/LanguageRuntime/CPlusPlus/CPPLanguageRuntime.cpp
index e562266e80d23..27aa2ce07a374 100644
--- a/lldb/source/Plugins/LanguageRuntime/CPlusPlus/CPPLanguageRuntime.cpp
+++ b/lldb/source/Plugins/LanguageRuntime/CPlusPlus/CPPLanguageRuntime.cpp
@@ -806,9 +806,9 @@ CPPLanguageRuntime::GetVTableInfoEntry(ValueObject &in_value, bool check_type) {
 
   // Check our cache first to see if we already have this info
   {
-    std::lock_guard<std::mutex> locker(m_vtable_mutex);
-    auto pos = m_vtable_info_map.find(vtable_addr);
-    if (pos != m_vtable_info_map.end())
+    auto vtable_info_map = m_vtable_info_map.Lock();
+    auto pos = vtable_info_map->find(vtable_addr);
+    if (pos != vtable_info_map->end())
       return pos->second;
   }
 
@@ -830,8 +830,7 @@ CPPLanguageRuntime::GetVTableInfoEntry(ValueObject &in_value, bool check_type) {
           /*info=*/VTableInfo{vtable_addr, symbol},
           /*runtime=*/runtime.get(),
       };
-      std::lock_guard<std::mutex> locker(m_vtable_mutex);
-      m_vtable_info_map[vtable_addr] = entry;
+      (*m_vtable_info_map.Lock())[vtable_addr] = entry;
       return entry;
     }
   }
diff --git a/lldb/source/Plugins/LanguageRuntime/CPlusPlus/CPPLanguageRuntime.h b/lldb/source/Plugins/LanguageRuntime/CPlusPlus/CPPLanguageRuntime.h
index 823a968cbad8c..5bc21448ce306 100644
--- a/lldb/source/Plugins/LanguageRuntime/CPlusPlus/CPPLanguageRuntime.h
+++ b/lldb/source/Plugins/LanguageRuntime/CPlusPlus/CPPLanguageRuntime.h
@@ -16,6 +16,7 @@
 #include "CommonABIRuntime.h"
 #include "lldb/Core/PluginInterface.h"
 #include "lldb/Target/LanguageRuntime.h"
+#include "lldb/Utility/Locked.h"
 #include "lldb/lldb-private.h"
 
 namespace lldb_private {
@@ -153,8 +154,8 @@ class CPPLanguageRuntime : public LanguageRuntime {
   llvm::Expected<VTableInfoEntry> GetVTableInfoEntry(ValueObject &in_value,
                                                      bool check_type);
 
-  std::map<Address, VTableInfoEntry> m_vtable_info_map;
-  std::mutex m_vtable_mutex;
+  using VTableInfoMap = std::map<Address, VTableInfoEntry>;
+  Guarded<VTableInfoMap, std::mutex> m_vtable_info_map;
 };
 
 } // namespace lldb_private
diff --git a/lldb/unittests/Utility/LockedTest.cpp b/lldb/unittests/Utility/LockedTest.cpp
index cae24293dee2e..f898f21b56291 100644
--- a/lldb/unittests/Utility/LockedTest.cpp
+++ b/lldb/unittests/Utility/LockedTest.cpp
@@ -225,3 +225,40 @@ TEST(LockedTest, ExclusiveAccessOnRWMutex) {
   writer->value = 11;
   EXPECT_EQ(widget.value, 11);
 }
+
+// Guarded is neither copyable nor movable.
+static_assert(!std::is_copy_constructible_v<Guarded<Widget>>);
+static_assert(!std::is_move_constructible_v<Guarded<Widget>>);
+
+TEST(LockedTest, GuardedDefaultConstructed) {
+  Guarded<Widget> guarded;
+  EXPECT_EQ(guarded.Lock()->value, 0);
+}
+
+TEST(LockedTest, GuardedValueConstructed) {
+  Guarded<Widget> guarded(Widget{42});
+  EXPECT_EQ(guarded.Lock()->value, 42);
+}
+
+TEST(LockedTest, GuardedExclusiveAccessMutatesValue) {
+  Guarded<Widget> guarded;
+  guarded.Lock()->value = 7;
+  EXPECT_EQ(guarded.Lock()->value, 7);
+}
+
+TEST(LockedTest, GuardedSharedAccessIsReadOnly) {
+  Guarded<Widget> guarded(Widget{5});
+  SharedLocked<const Widget *, llvm::sys::RWMutex> reader =
+      guarded.LockShared();
+  EXPECT_EQ(reader->value, 5);
+  static_assert(std::is_same_v<decltype(reader.get()), const Widget *>,
+                "shared access borrows a const-qualified pointer");
+}
+
+// std::shared_mutex satisfies SharedLockable too, so Guarded works with it
+// as a drop-in replacement for llvm::sys::RWMutex.
+TEST(LockedTest, GuardedWorksWithStdSharedMutex) {
+  Guarded<Widget, std::shared_mutex> guarded;
+  guarded.Lock()->value = 3;
+  EXPECT_EQ(guarded.LockShared()->value, 3);
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/219428