Enable thread safety annotations in open source version.

The thread safety annotations used by leveldb got opensourced in Abseil
[1]. This CL replaces leveldb's stubs with the relevant definitions from
[1], and adds annotations to the Mutex classes in the POSIX port.

[1] https://github.com/abseil/abseil-cpp/blob/master/absl/base/thread_annotations.h

build_detect_platform

@@ -202,7 +202,6 @@ EOF
         PLATFORM_LIBS="$PLATFORM_LIBS -lcrc32c"
     fi
 
-
     # Test whether Snappy library is installed
     # https://github.com/google/snappy
     $CXX $CXXFLAGS -x c++ - -o $CXXOUTPUT 2>/dev/null  <<EOF
@@ -222,7 +221,23 @@ EOF
         PLATFORM_LIBS="$PLATFORM_LIBS -ltcmalloc"
     fi
 
-    rm -f $CXXOUTPUT 2>/dev/null
+    # Test whether -Wthread-safety is available. See
+    # https://clang.llvm.org/docs/ThreadSafetyAnalysis.html
+    # -Werror is necessary because unknown attributes only generate warnings.
+    $CXX $CXXFLAGS -Wthread-safety -Werror -x c++ - -o $CXXOUTPUT 2>/dev/null  <<EOF
+      struct __attribute__((lockable)) Lock {
+        void Acquire() __attribute__((exclusive_lock_function()));
+        void Release() __attribute__((unlock_function()));
+      };
+      struct ThreadSafeType {
+        Lock lock_;
+        int data_ __attribute__((guarded_by(lock_)));
+      };
+      int main() { return 0; }
+EOF
+    if [ "$?" = 0 ]; then
+        COMMON_FLAGS="$COMMON_FLAGS -Wthread-safety"
+    fi
 
     rm -f $CXXOUTPUT 2>/dev/null
 fi

port/port_example.h

@@ -10,6 +10,8 @@
 #ifndef STORAGE_LEVELDB_PORT_PORT_EXAMPLE_H_
 #define STORAGE_LEVELDB_PORT_PORT_EXAMPLE_H_
 
+#include "port/thread_annotations.h"
+
 namespace leveldb {
 namespace port {
 
@@ -23,23 +25,23 @@ static const bool kLittleEndian = true /* or some other expression */;
 // ------------------ Threading -------------------
 
 // A Mutex represents an exclusive lock.
-class Mutex {
+class LOCKABLE Mutex {
  public:
   Mutex();
   ~Mutex();
 
   // Lock the mutex.  Waits until other lockers have exited.
   // Will deadlock if the mutex is already locked by this thread.
-  void Lock();
+  void Lock() EXCLUSIVE_LOCK_FUNCTION();
 
   // Unlock the mutex.
   // REQUIRES: This mutex was locked by this thread.
-  void Unlock();
+  void Unlock() UNLOCK_FUNCTION();
 
   // Optionally crash if this thread does not hold this mutex.
   // The implementation must be fast, especially if NDEBUG is
   // defined.  The implementation is allowed to skip all checks.
-  void AssertHeld();
+  void AssertHeld() ASSERT_EXCLUSIVE_LOCK();
 };
 
 class CondVar {

port/port_posix.h

@@ -48,6 +48,7 @@
 #include <stdint.h>
 #include <string>
 #include "port/atomic_pointer.h"
+#include "port/thread_annotations.h"
 
 #ifndef PLATFORM_IS_LITTLE_ENDIAN
 #define PLATFORM_IS_LITTLE_ENDIAN (__BYTE_ORDER == __LITTLE_ENDIAN)
@@ -73,14 +74,14 @@ static const bool kLittleEndian = PLATFORM_IS_LITTLE_ENDIAN;
 
 class CondVar;
 
-class Mutex {
+class LOCKABLE Mutex {
  public:
   Mutex();
   ~Mutex();
 
-  void Lock();
+  void Lock() EXCLUSIVE_LOCK_FUNCTION();
-  void Unlock();
+  void Unlock() UNLOCK_FUNCTION();
-  void AssertHeld() { }
+  void AssertHeld() ASSERT_EXCLUSIVE_LOCK() { }
 
  private:
   friend class CondVar;

port/thread_annotations.h

@@ -5,56 +5,107 @@
 #ifndef STORAGE_LEVELDB_PORT_THREAD_ANNOTATIONS_H_
 #define STORAGE_LEVELDB_PORT_THREAD_ANNOTATIONS_H_
 
-// Some environments provide custom macros to aid in static thread-safety
+// Use Clang's thread safety analysis annotations when available. In other
-// analysis.  Provide empty definitions of such macros unless they are already
+// environments, the macros receive empty definitions.
-// defined.
+// Usage documentation: https://clang.llvm.org/docs/ThreadSafetyAnalysis.html
+
+#if !defined(THREAD_ANNOTATION_ATTRIBUTE__)
+
+#if defined(__clang__)
+
+#define THREAD_ANNOTATION_ATTRIBUTE__(x)   __attribute__((x))
+#else
+#define THREAD_ANNOTATION_ATTRIBUTE__(x)   // no-op
+#endif
+
+#endif  // !defined(THREAD_ANNOTATION_ATTRIBUTE__)
+
+#ifndef GUARDED_BY
+#define GUARDED_BY(x) THREAD_ANNOTATION_ATTRIBUTE__(guarded_by(x))
+#endif
+
+#ifndef PT_GUARDED_BY
+#define PT_GUARDED_BY(x) THREAD_ANNOTATION_ATTRIBUTE__(pt_guarded_by(x))
+#endif
+
+#ifndef ACQUIRED_AFTER
+#define ACQUIRED_AFTER(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(acquired_after(__VA_ARGS__))
+#endif
+
+#ifndef ACQUIRED_BEFORE
+#define ACQUIRED_BEFORE(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(acquired_before(__VA_ARGS__))
+#endif
 
 #ifndef EXCLUSIVE_LOCKS_REQUIRED
-#define EXCLUSIVE_LOCKS_REQUIRED(...)
+#define EXCLUSIVE_LOCKS_REQUIRED(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(exclusive_locks_required(__VA_ARGS__))
 #endif
 
 #ifndef SHARED_LOCKS_REQUIRED
-#define SHARED_LOCKS_REQUIRED(...)
+#define SHARED_LOCKS_REQUIRED(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(shared_locks_required(__VA_ARGS__))
 #endif
 
 #ifndef LOCKS_EXCLUDED
-#define LOCKS_EXCLUDED(...)
+#define LOCKS_EXCLUDED(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(locks_excluded(__VA_ARGS__))
 #endif
 
 #ifndef LOCK_RETURNED
-#define LOCK_RETURNED(x)
+#define LOCK_RETURNED(x) \
+  THREAD_ANNOTATION_ATTRIBUTE__(lock_returned(x))
 #endif
 
 #ifndef LOCKABLE
-#define LOCKABLE
+#define LOCKABLE \
+  THREAD_ANNOTATION_ATTRIBUTE__(lockable)
 #endif
 
 #ifndef SCOPED_LOCKABLE
-#define SCOPED_LOCKABLE
+#define SCOPED_LOCKABLE \
+  THREAD_ANNOTATION_ATTRIBUTE__(scoped_lockable)
 #endif
 
 #ifndef EXCLUSIVE_LOCK_FUNCTION
-#define EXCLUSIVE_LOCK_FUNCTION(...)
+#define EXCLUSIVE_LOCK_FUNCTION(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(exclusive_lock_function(__VA_ARGS__))
 #endif
 
 #ifndef SHARED_LOCK_FUNCTION
-#define SHARED_LOCK_FUNCTION(...)
+#define SHARED_LOCK_FUNCTION(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(shared_lock_function(__VA_ARGS__))
 #endif
 
 #ifndef EXCLUSIVE_TRYLOCK_FUNCTION
-#define EXCLUSIVE_TRYLOCK_FUNCTION(...)
+#define EXCLUSIVE_TRYLOCK_FUNCTION(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(exclusive_trylock_function(__VA_ARGS__))
 #endif
 
 #ifndef SHARED_TRYLOCK_FUNCTION
-#define SHARED_TRYLOCK_FUNCTION(...)
+#define SHARED_TRYLOCK_FUNCTION(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(shared_trylock_function(__VA_ARGS__))
 #endif
 
 #ifndef UNLOCK_FUNCTION
-#define UNLOCK_FUNCTION(...)
+#define UNLOCK_FUNCTION(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(unlock_function(__VA_ARGS__))
 #endif
 
 #ifndef NO_THREAD_SAFETY_ANALYSIS
-#define NO_THREAD_SAFETY_ANALYSIS
+#define NO_THREAD_SAFETY_ANALYSIS \
+  THREAD_ANNOTATION_ATTRIBUTE__(no_thread_safety_analysis)
+#endif
+
+#ifndef ASSERT_EXCLUSIVE_LOCK
+#define ASSERT_EXCLUSIVE_LOCK(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(assert_exclusive_lock(__VA_ARGS__))
+#endif
+
+#ifndef ASSERT_SHARED_LOCK
+#define ASSERT_SHARED_LOCK(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(assert_shared_lock(__VA_ARGS__))
 #endif
 
 #endif  // STORAGE_LEVELDB_PORT_THREAD_ANNOTATIONS_H_