tor-browser

thread_collision_warner.h (7877B)

---

// Copyright 2012 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef BASE_THREADING_THREAD_COLLISION_WARNER_H_
#define BASE_THREADING_THREAD_COLLISION_WARNER_H_

#include "base/atomicops.h"
#include "base/base_export.h"
#include "base/compiler_specific.h"
#include "base/macros/uniquify.h"
#include "base/memory/raw_ptr.h"

// A helper class alongside macros to be used to verify assumptions about thread
// safety of a class.
//
// Example: Queue implementation non thread-safe but still usable if clients
//          are synchronized somehow.
//
//          In this case the macro DFAKE_SCOPED_LOCK has to be
//          used, it checks that if a thread is inside the push/pop then
//          noone else is still inside the pop/push
//
// class NonThreadSafeQueue {
//  public:
//   ...
//   void push(int) { DFAKE_SCOPED_LOCK(push_pop_); ... }
//   int pop() { DFAKE_SCOPED_LOCK(push_pop_); ... }
//   ...
//  private:
//   DFAKE_MUTEX(push_pop_);
// };
//
//
// Example: Queue implementation non thread-safe but still usable if clients
//          are synchronized somehow, it calls a method to "protect" from
//          a "protected" method
//
//          In this case the macro DFAKE_SCOPED_RECURSIVE_LOCK
//          has to be used, it checks that if a thread is inside the push/pop
//          then noone else is still inside the pop/push
//
// class NonThreadSafeQueue {
//  public:
//   void push(int) {
//     DFAKE_SCOPED_LOCK(push_pop_);
//     ...
//   }
//   int pop() {
//     DFAKE_SCOPED_RECURSIVE_LOCK(push_pop_);
//     bar();
//     ...
//   }
//   void bar() { DFAKE_SCOPED_RECURSIVE_LOCK(push_pop_); ... }
//   ...
//  private:
//   DFAKE_MUTEX(push_pop_);
// };
//
//
// Example: Queue implementation not usable even if clients are synchronized,
//          so only one thread in the class life cycle can use the two members
//          push/pop.
//
//          In this case the macro DFAKE_SCOPED_LOCK_THREAD_LOCKED pins the
//          specified
//          critical section the first time a thread enters push or pop, from
//          that time on only that thread is allowed to execute push or pop.
//
// class NonThreadSafeQueue {
//  public:
//   ...
//   void push(int) { DFAKE_SCOPED_LOCK_THREAD_LOCKED(push_pop_); ... }
//   int pop() { DFAKE_SCOPED_LOCK_THREAD_LOCKED(push_pop_); ... }
//   ...
//  private:
//   DFAKE_MUTEX(push_pop_);
// };
//
//
// Example: Class that has to be contructed/destroyed on same thread, it has
//          a "shareable" method (with external synchronization) and a not
//          shareable method (even with external synchronization).
//
//          In this case 3 Critical sections have to be defined
//
// class ExoticClass {
//  public:
//   ExoticClass() { DFAKE_SCOPED_LOCK_THREAD_LOCKED(ctor_dtor_); ... }
//   ~ExoticClass() { DFAKE_SCOPED_LOCK_THREAD_LOCKED(ctor_dtor_); ... }
//
//   void Shareable() { DFAKE_SCOPED_LOCK(shareable_section_); ... }
//   void NotShareable() { DFAKE_SCOPED_LOCK_THREAD_LOCKED(ctor_dtor_); ... }
//   ...
//  private:
//   DFAKE_MUTEX(ctor_dtor_);
//   DFAKE_MUTEX(shareable_section_);
// };

#if !defined(NDEBUG)

// Defines a class member that acts like a mutex. It is used only as a
// verification tool.
#define DFAKE_MUTEX(obj) \
    mutable base::ThreadCollisionWarner obj
// Asserts the call is never called simultaneously in two threads. Used at
// member function scope.
#define DFAKE_SCOPED_LOCK(obj) \
 base::ThreadCollisionWarner::ScopedCheck BASE_UNIQUIFY(s_check_)(&obj)
// Asserts the call is never called simultaneously in two threads. Used at
// member function scope. Same as DFAKE_SCOPED_LOCK but allows recursive locks.
#define DFAKE_SCOPED_RECURSIVE_LOCK(obj)                                     \
 base::ThreadCollisionWarner::ScopedRecursiveCheck BASE_UNIQUIFY(sr_check)( \
     &obj)
// Asserts the code is always executed in the same thread.
#define DFAKE_SCOPED_LOCK_THREAD_LOCKED(obj) \
 base::ThreadCollisionWarner::Check BASE_UNIQUIFY(check_)(&obj)

#else

#define DFAKE_MUTEX(obj) typedef void InternalFakeMutexType##obj
#define DFAKE_SCOPED_LOCK(obj) ((void)0)
#define DFAKE_SCOPED_RECURSIVE_LOCK(obj) ((void)0)
#define DFAKE_SCOPED_LOCK_THREAD_LOCKED(obj) ((void)0)

#endif

namespace base {

// The class ThreadCollisionWarner uses an Asserter to notify the collision
// AsserterBase is the interfaces and DCheckAsserter is the default asserter
// used. During the unit tests is used another class that doesn't "DCHECK"
// in case of collision (check thread_collision_warner_unittests.cc)
struct BASE_EXPORT AsserterBase {
 virtual ~AsserterBase() = default;
 virtual void warn() = 0;
};

struct BASE_EXPORT DCheckAsserter : public AsserterBase {
 ~DCheckAsserter() override = default;
 void warn() override;
};

class BASE_EXPORT ThreadCollisionWarner {
public:
 // The parameter asserter is there only for test purpose
 explicit ThreadCollisionWarner(AsserterBase* asserter = new DCheckAsserter())
     : valid_thread_id_(0),
       counter_(0),
       asserter_(asserter) {}

 ThreadCollisionWarner(const ThreadCollisionWarner&) = delete;
 ThreadCollisionWarner& operator=(const ThreadCollisionWarner&) = delete;

 ~ThreadCollisionWarner() { asserter_.ClearAndDelete(); }

 // This class is meant to be used through the macro
 // DFAKE_SCOPED_LOCK_THREAD_LOCKED
 // it doesn't leave the critical section, as opposed to ScopedCheck,
 // because the critical section being pinned is allowed to be used only
 // from one thread
 class BASE_EXPORT Check {
  public:
   explicit Check(ThreadCollisionWarner* warner)
       : warner_(warner) {
     warner_->EnterSelf();
   }

   Check(const Check&) = delete;
   Check& operator=(const Check&) = delete;

   ~Check() = default;

  private:
   raw_ptr<ThreadCollisionWarner> warner_;
 };

 // This class is meant to be used through the macro
 // DFAKE_SCOPED_LOCK
 class BASE_EXPORT ScopedCheck {
  public:
   explicit ScopedCheck(ThreadCollisionWarner* warner)
       : warner_(warner) {
     warner_->Enter();
   }

   ScopedCheck(const ScopedCheck&) = delete;
   ScopedCheck& operator=(const ScopedCheck&) = delete;

   ~ScopedCheck() {
     warner_->Leave();
   }

  private:
   raw_ptr<ThreadCollisionWarner> warner_;
 };

 // This class is meant to be used through the macro
 // DFAKE_SCOPED_RECURSIVE_LOCK
 class BASE_EXPORT ScopedRecursiveCheck {
  public:
   explicit ScopedRecursiveCheck(ThreadCollisionWarner* warner)
       : warner_(warner) {
     warner_->EnterSelf();
   }

   ScopedRecursiveCheck(const ScopedRecursiveCheck&) = delete;
   ScopedRecursiveCheck& operator=(const ScopedRecursiveCheck&) = delete;

   ~ScopedRecursiveCheck() {
     warner_->Leave();
   }

  private:
   raw_ptr<ThreadCollisionWarner> warner_;
 };

private:
 // This method stores the current thread identifier and does a DCHECK
 // if a another thread has already done it, it is safe if same thread
 // calls this multiple time (recursion allowed).
 void EnterSelf();

 // Same as EnterSelf but recursion is not allowed.
 void Enter();

 // Removes the thread_id stored in order to allow other threads to
 // call EnterSelf or Enter.
 void Leave();

 // This stores the thread id that is inside the critical section, if the
 // value is 0 then no thread is inside.
 volatile subtle::Atomic32 valid_thread_id_;

 // Counter to trace how many time a critical section was "pinned"
 // (when allowed) in order to unpin it when counter_ reaches 0.
 volatile subtle::Atomic32 counter_;

 // Here only for class unit tests purpose, during the test I need to not
 // DCHECK but notify the collision with something else.
 raw_ptr<AsserterBase> asserter_;
};

}  // namespace base

#endif  // BASE_THREADING_THREAD_COLLISION_WARNER_H_