// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// 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 <memory>
#include "base/atomicops.h"
#include "base/base_export.h"
#include "base/basictypes.h"
#include "base/compiler_specific.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 s_check_##obj(&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 sr_check_##obj(&obj)
// Asserts the code is always executed in the same thread.
#define DFAKE_SCOPED_LOCK_THREAD_LOCKED(obj) \
base::ThreadCollisionWarner::Check check_##obj(&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() {}
virtual void warn() = 0;
};
struct BASE_EXPORT DCheckAsserter : public AsserterBase {
virtual ~DCheckAsserter() {}
virtual 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() {
delete asserter_;
}
// 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() {}
private:
ThreadCollisionWarner* warner_;
DISALLOW_COPY_AND_ASSIGN(Check);
};
// 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() {
warner_->Leave();
}
private:
ThreadCollisionWarner* warner_;
DISALLOW_COPY_AND_ASSIGN(ScopedCheck);
};
// 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() {
warner_->Leave();
}
private:
ThreadCollisionWarner* warner_;
DISALLOW_COPY_AND_ASSIGN(ScopedRecursiveCheck);
};
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.
AsserterBase* asserter_;
DISALLOW_COPY_AND_ASSIGN(ThreadCollisionWarner);
};
} // namespace base
#endif // BASE_THREADING_THREAD_COLLISION_WARNER_H_