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// ---
// Author: Le-Chun Wu
//
// 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 clang's "attributes" extension.
// Using the macros defined here instead of the raw clang attributes allows
// for portability and future compatibility.
//
// This functionality is not yet fully implemented in perftools,
// but may be one day.

#ifndef BASE_THREAD_ANNOTATIONS_H_
#define BASE_THREAD_ANNOTATIONS_H_


#if defined(__clang__)
#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 lock.
// GUARDED_BY allows the user to specify a particular lock that should be
// held when accessing the annotated variable, while GUARDED_VAR only
// indicates a shared variable should be guarded (by any lock). GUARDED_VAR
// is primarily used when the client cannot express the name of the lock.
#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 lock when dereferencing the pointer. Similar to GUARDED_VAR,
// PT_GUARDED_VAR is primarily used when the client cannot express the name
// of the lock. 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__(point_to_guarded_by(x))
#define PT_GUARDED_VAR \
  THREAD_ANNOTATION_ATTRIBUTE__(point_to_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(x) \
  THREAD_ANNOTATION_ATTRIBUTE__(acquired_after(x))
#define ACQUIRED_BEFORE(x) \
  THREAD_ANNOTATION_ATTRIBUTE__(acquired_before(x))

// The following three annotations document the lock requirements for
// functions/methods.

// Document if a function expects certain locks to be held before it is called
#define EXCLUSIVE_LOCKS_REQUIRED(x) \
  THREAD_ANNOTATION_ATTRIBUTE__(exclusive_locks_required(x))

#define SHARED_LOCKS_REQUIRED(x) \
  THREAD_ANNOTATION_ATTRIBUTE__(shared_locks_required(x))

// 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(x) \
  THREAD_ANNOTATION_ATTRIBUTE__(locks_excluded(x))

// Document the lock the annotated function returns without acquiring it.
#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 is a scoped lockable type (such as the MutexLock class).
#define SCOPED_LOCKABLE        THREAD_ANNOTATION_ATTRIBUTE__(scoped_lockable)

// The following annotations specify lock and unlock primitives.
#define EXCLUSIVE_LOCK_FUNCTION(x) \
  THREAD_ANNOTATION_ATTRIBUTE__(exclusive_lock_function(x))

#define SHARED_LOCK_FUNCTION(x) \
  THREAD_ANNOTATION_ATTRIBUTE__(shared_lock_function(x))

#define EXCLUSIVE_TRYLOCK_FUNCTION(x) \
  THREAD_ANNOTATION_ATTRIBUTE__(exclusive_trylock_function(x))

#define SHARED_TRYLOCK_FUNCTION(x) \
  THREAD_ANNOTATION_ATTRIBUTE__(shared_trylock_function(x))

#define UNLOCK_FUNCTION(x) \
  THREAD_ANNOTATION_ATTRIBUTE__(unlock_function(x))

// An escape hatch for thread safety analysis to ignore the annotated function.
#define NO_THREAD_SAFETY_ANALYSIS \
  THREAD_ANNOTATION_ATTRIBUTE__(no_thread_safety_analysis)

#endif  // BASE_THREAD_ANNOTATIONS_H_
