client/base/thread_annotations.h

/*
  Copyright 2014 Google Inc.

  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
*/

// ---
//
// This header file contains the macro definitions for thread safety
// annotations that allow the developers to document the locking policies
// of their multi-threaded code. The annotations can also help program
// analysis tools to identify potential thread safety issues.
//
// The annotations are implemented using GCC's "attributes" extension.
// Using the macros defined here instead of the raw GCC attributes allows
// for portability and future compatibility.
//

#ifndef BASE_THREAD_ANNOTATIONS_H_
#define BASE_THREAD_ANNOTATIONS_H_

#if defined(__clang__) && (!defined(SWIG))
#define THREAD_ANNOTATION_ATTRIBUTE__(x)   __attribute__((x))
#else
#define THREAD_ANNOTATION_ATTRIBUTE__(x)   // no-op
#endif

// Document if a shared variable/field needs to be protected by a mutex.
// GUARDED_BY allows the user to specify a particular mutex that should be
// held when accessing the annotated variable.  GUARDED_VAR indicates that
// a shared variable is guarded by some unspecified mutex, for use in rare
// cases where a valid mutex expression cannot be specified.
#define GUARDED_BY(x) THREAD_ANNOTATION_ATTRIBUTE__(guarded_by(x))
#define GUARDED_VAR   THREAD_ANNOTATION_ATTRIBUTE__(guarded)

// Document if the memory location pointed to by a pointer should be guarded
// by a mutex when dereferencing the pointer.  PT_GUARDED_VAR is analagous to
// GUARDED_VAR.   Note that a pointer variable to a shared memory location
// could itself be a shared variable. For example, if a shared global pointer
// q, which is guarded by mu1, points to a shared memory location that is
// guarded by mu2, q should be annotated as follows:
//     int *q GUARDED_BY(mu1) PT_GUARDED_BY(mu2);
#define PT_GUARDED_BY(x) THREAD_ANNOTATION_ATTRIBUTE__(pt_guarded_by(x))
#define PT_GUARDED_VAR   THREAD_ANNOTATION_ATTRIBUTE__(pt_guarded)

// Document the acquisition order between locks that can be held
// simultaneously by a thread. For any two locks that need to be annotated
// to establish an acquisition order, only one of them needs the annotation.
// (i.e. You don't have to annotate both locks with both ACQUIRED_AFTER
// and ACQUIRED_BEFORE.)
#define ACQUIRED_AFTER(...) \
  THREAD_ANNOTATION_ATTRIBUTE__(acquired_after(__VA_ARGS__))

#define ACQUIRED_BEFORE(...) \
  THREAD_ANNOTATION_ATTRIBUTE__(acquired_before(__VA_ARGS__))

// Document a function that expects a mutex to be held prior to entry.
// The mutex is expected to be held both on entry to and exit from the
// function.
#define EXCLUSIVE_LOCKS_REQUIRED(...) \
  THREAD_ANNOTATION_ATTRIBUTE__(exclusive_locks_required(__VA_ARGS__))

#define SHARED_LOCKS_REQUIRED(...) \
  THREAD_ANNOTATION_ATTRIBUTE__(shared_locks_required(__VA_ARGS__))

// Document the locks acquired in the body of the function. These locks
// cannot be held when calling this function (as google3's Mutex locks are
// non-reentrant).
#define LOCKS_EXCLUDED(...) \
  THREAD_ANNOTATION_ATTRIBUTE__(locks_excluded(__VA_ARGS__))

// Document a function that returns a mutex without acquiring it.  For example,
// a public getter method that returns a pointer to a private mutex should
// be annotated with LOCK_RETURNED.
#define LOCK_RETURNED(x) \
  THREAD_ANNOTATION_ATTRIBUTE__(lock_returned(x))

// Document if a class/type is a lockable type (such as the Mutex class).
#define LOCKABLE \
  THREAD_ANNOTATION_ATTRIBUTE__(lockable)

// Document if a class does RAII locking (such as the MutexLock class).
// The constructor should use LOCK_FUNCTION to specify the mutex that is
// acquired, and the destructor should use UNLOCK_FUNCTION with no arguments;
// the analysis will assume that the destructor unlocks whatever the
// constructor locked.
#define SCOPED_LOCKABLE \
  THREAD_ANNOTATION_ATTRIBUTE__(scoped_lockable)

// Document functions that acquire a lock in the body of a function, and do
// not release it.
#define EXCLUSIVE_LOCK_FUNCTION(...) \
  THREAD_ANNOTATION_ATTRIBUTE__(exclusive_lock_function(__VA_ARGS__))

#define SHARED_LOCK_FUNCTION(...) \
  THREAD_ANNOTATION_ATTRIBUTE__(shared_lock_function(__VA_ARGS__))

// Document functions that expect a lock to be held on entry to the function,
// and release it in the body of the function.
#define UNLOCK_FUNCTION(...) \
  THREAD_ANNOTATION_ATTRIBUTE__(unlock_function(__VA_ARGS__))

// Document functions that try to acquire a lock, and return success or failure.
// The first argument should be true, for functions that return true on success,
// or false, for functions that return false on success.
#define EXCLUSIVE_TRYLOCK_FUNCTION(...) \
  THREAD_ANNOTATION_ATTRIBUTE__(exclusive_trylock_function(__VA_ARGS__))

#define SHARED_TRYLOCK_FUNCTION(...) \
  THREAD_ANNOTATION_ATTRIBUTE__(shared_trylock_function(__VA_ARGS__))

// Document functions that dynamically check to see if a lock is held, and fail
// if it is not held.
#define ASSERT_EXCLUSIVE_LOCK(...) \
  THREAD_ANNOTATION_ATTRIBUTE__(assert_exclusive_lock(__VA_ARGS__))

#define ASSERT_SHARED_LOCK(...) \
  THREAD_ANNOTATION_ATTRIBUTE__(assert_shared_lock(__VA_ARGS__))

// Turns off thread safety checking within the body of a particular function.
// This is used as an escape hatch for cases where either (a) the function
// is correct, but the locking is more complicated than the analyzer can handle,
// or (b) the function contains race conditions that are known to be benign.
#define NO_THREAD_SAFETY_ANALYSIS \
  THREAD_ANNOTATION_ATTRIBUTE__(no_thread_safety_analysis)

// Deprecated.
// NO_THREAD_SAFETY_ANALYSIS_OPT  is a workaround for bugs gcc annotalysis.
// TODO(delesley): remove all uses of this macro in google3.
#define NO_THREAD_SAFETY_ANALYSIS_OPT

// TS_UNCHECKED should be placed around lock expressions that are not valid
// C++ syntax, but which are present for documentation purposes.  These
// annotations will be ignored by the analysis.
#define TS_UNCHECKED(x) ""

// Deprecated.
// This is used to pass different annotations to gcc and clang, in cases where
// gcc would reject a lock expression (e.g. &MyClass::mu_) that is accepted
// by clang.  This is seldom needed, since GCC usually ignores invalid lock
// expressions except in certain cases, such as LOCK_RETURNED.
// TODO(delesley): remove all uses of this macro from google.
#define TS_CLANG_ONLY(CLANG_EXPR, GCC_EXPR) CLANG_EXPR

// TS_FIXME is used to mark lock expressions that are not valid C++ syntax.
// It is used by automated tools to mark and disable invalid expressions.
// The annotation should either be fixed, or changed to TS_UNCHECKED.
#define TS_FIXME(x) ""

// Like NO_THREAD_SAFETY_ANALYSIS, this turns off checking within the body of
// a particular function.  However, this attribute is used to mark functions
// that are incorrect and need to be fixed.  It is used by automated tools to
// avoid breaking the build when the analysis is updated.
// Code owners are expected to eventually fix the routine.
#define NO_THREAD_SAFETY_ANALYSIS_FIXME  NO_THREAD_SAFETY_ANALYSIS

// Similar to NO_THREAD_SAFETY_ANALYSIS_FIXME, this macro marks a GUARDED_BY
// annotation that needs to be fixed, because it is producing thread safety
// warning.  It disables the GUARDED_BY.
#define GUARDED_BY_FIXME(x)

// Disables warnings for a single read operation.  This can be used to do racy
// reads of guarded data members, in cases where the race is benign.
#define TS_UNCHECKED_READ(x) thread_safety_analysis::ts_unchecked_read(x)

namespace thread_safety_analysis {

// Takes a reference to a guarded data member, and returns an unguarded
// reference.
template <class T>
inline const T& ts_unchecked_read(const T& v) NO_THREAD_SAFETY_ANALYSIS {
  return v;
}

template <class T>
inline T& ts_unchecked_read(T& v) NO_THREAD_SAFETY_ANALYSIS {
  return v;
}

}  // namespace thread_safety_analysis

#endif  // BASE_THREAD_ANNOTATIONS_H_