зеркало из https://github.com/mozilla/gecko-dev.git
144 строки
4.4 KiB
C++
144 строки
4.4 KiB
C++
/* This Source Code Form is subject to the terms of the Mozilla Public
|
|
* License, v. 2.0. If a copy of the MPL was not distributed with this
|
|
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
|
|
|
|
// A class for values only accessible from a single designated thread.
|
|
|
|
#ifndef mozilla_ThreadBound_h
|
|
#define mozilla_ThreadBound_h
|
|
|
|
#include "mozilla/Atomics.h"
|
|
#include "prthread.h"
|
|
|
|
#include <type_traits>
|
|
|
|
namespace mozilla {
|
|
|
|
template <typename T>
|
|
class ThreadBound;
|
|
|
|
namespace detail {
|
|
|
|
template <bool Condition, typename T>
|
|
struct AddConstIf {
|
|
using type = T;
|
|
};
|
|
|
|
template <typename T>
|
|
struct AddConstIf<true, T> {
|
|
using type = typename std::add_const<T>::type;
|
|
};
|
|
|
|
} // namespace detail
|
|
|
|
// A ThreadBound<T> is a T that can only be accessed by a specific
|
|
// thread. To enforce this rule, the inner T is only accessible
|
|
// through a non-copyable, immovable accessor object.
|
|
// Given a ThreadBound<T> threadBoundData, it can be accessed like so:
|
|
//
|
|
// auto innerData = threadBoundData.Access();
|
|
// innerData->DoStuff();
|
|
//
|
|
// Trying to access a ThreadBound<T> from a different thread will
|
|
// trigger a MOZ_DIAGNOSTIC_ASSERT.
|
|
// The encapsulated T is constructed during the construction of the
|
|
// enclosing ThreadBound<T> by forwarding all of the latter's
|
|
// constructor parameters to the former. A newly constructed
|
|
// ThreadBound<T> is bound to the thread it's constructed in. It's
|
|
// possible to rebind the data to some otherThread by calling
|
|
//
|
|
// threadBoundData.Transfer(otherThread);
|
|
//
|
|
// on the thread that threadBoundData is currently bound to, as long
|
|
// as it's not currently being accessed. (Trying to rebind from
|
|
// another thread or while an accessor exists will trigger an
|
|
// assertion.)
|
|
//
|
|
// Note: A ThreadBound<T> may be destructed from any thread, not just
|
|
// its designated thread at the time the destructor is invoked.
|
|
template <typename T>
|
|
class ThreadBound final {
|
|
public:
|
|
template <typename... Args>
|
|
explicit ThreadBound(Args&&... aArgs)
|
|
: mData(std::forward<Args>(aArgs)...),
|
|
mThread(PR_GetCurrentThread()),
|
|
mAccessCount(0) {}
|
|
|
|
~ThreadBound() { AssertIsNotCurrentlyAccessed(); }
|
|
|
|
void Transfer(const PRThread* const aDest) {
|
|
AssertIsCorrectThread();
|
|
AssertIsNotCurrentlyAccessed();
|
|
mThread = aDest;
|
|
}
|
|
|
|
private:
|
|
T mData;
|
|
|
|
// This member is (potentially) accessed by multiple threads and is
|
|
// thus the first point of synchronization between them.
|
|
Atomic<const PRThread*, ReleaseAcquire> mThread;
|
|
|
|
// In order to support nested accesses (e.g. from different stack
|
|
// frames) it's necessary to maintain a counter of the existing
|
|
// accessor. Since it's possible to access a const ThreadBound, the
|
|
// counter is mutable. It's atomic because accessing it synchronizes
|
|
// access to mData (see comment in Accessor's constructor).
|
|
using AccessCountType = Atomic<int, ReleaseAcquire>;
|
|
mutable AccessCountType mAccessCount;
|
|
|
|
public:
|
|
template <bool IsConst>
|
|
class MOZ_STACK_CLASS Accessor final {
|
|
using DataType = typename detail::AddConstIf<IsConst, T>::type;
|
|
|
|
public:
|
|
explicit Accessor(
|
|
typename detail::AddConstIf<IsConst, ThreadBound>::type& aThreadBound)
|
|
: mData(aThreadBound.mData), mAccessCount(aThreadBound.mAccessCount) {
|
|
aThreadBound.AssertIsCorrectThread();
|
|
|
|
// This load/store serves as a memory fence that guards mData
|
|
// against accesses that would trip the thread assertion.
|
|
// (Otherwise one of the loads in the caller's instruction
|
|
// stream might be scheduled before the assertion.)
|
|
++mAccessCount;
|
|
}
|
|
|
|
Accessor(const Accessor&) = delete;
|
|
Accessor(Accessor&&) = delete;
|
|
Accessor& operator=(const Accessor&) = delete;
|
|
Accessor& operator=(Accessor&&) = delete;
|
|
|
|
~Accessor() { --mAccessCount; }
|
|
|
|
DataType* operator->() { return &mData; }
|
|
|
|
private:
|
|
DataType& mData;
|
|
AccessCountType& mAccessCount;
|
|
};
|
|
|
|
auto Access() { return Accessor<false>{*this}; }
|
|
|
|
auto Access() const { return Accessor<true>{*this}; }
|
|
|
|
private:
|
|
bool IsCorrectThread() const { return mThread == PR_GetCurrentThread(); }
|
|
|
|
bool IsNotCurrentlyAccessed() const { return mAccessCount == 0; }
|
|
|
|
#define MOZ_DEFINE_THREAD_BOUND_ASSERT(predicate) \
|
|
void Assert##predicate() const { MOZ_DIAGNOSTIC_ASSERT(predicate()); }
|
|
|
|
MOZ_DEFINE_THREAD_BOUND_ASSERT(IsCorrectThread)
|
|
MOZ_DEFINE_THREAD_BOUND_ASSERT(IsNotCurrentlyAccessed)
|
|
|
|
#undef MOZ_DEFINE_THREAD_BOUND_ASSERT
|
|
};
|
|
|
|
} // namespace mozilla
|
|
|
|
#endif // mozilla_ThreadBound_h
|