Revert "Move webrtc/{base => rtc_base}" (https://codereview.webrtc.org/2877023002)
Will reland in two different commits to preserve git blame history.
BUG=webrtc:7634
NOTRY=True
TBR=kwiberg@webrtc.org
Change-Id: I550da8525aeb9c5b8f96338fcf1c9714f3dcdab1
Reviewed-on: https://chromium-review.googlesource.com/554610
Reviewed-by: Henrik Kjellander <kjellander@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#18820}diff --git a/webrtc/base/weak_ptr.h b/webrtc/base/weak_ptr.h
index 282a551..28789d0 100644
--- a/webrtc/base/weak_ptr.h
+++ b/webrtc/base/weak_ptr.h
@@ -11,9 +11,262 @@
#ifndef WEBRTC_BASE_WEAK_PTR_H_
#define WEBRTC_BASE_WEAK_PTR_H_
+#include <memory>
-// This header is deprecated and is just left here temporarily during
-// refactoring. See https://bugs.webrtc.org/7634 for more details.
-#include "webrtc/rtc_base/weak_ptr.h"
+#include <utility>
+
+#include "webrtc/base/refcount.h"
+#include "webrtc/base/scoped_ref_ptr.h"
+#include "webrtc/base/sequenced_task_checker.h"
+
+// The implementation is borrowed from chromium except that it does not
+// implement SupportsWeakPtr.
+
+// Weak pointers are pointers to an object that do not affect its lifetime,
+// and which may be invalidated (i.e. reset to nullptr) by the object, or its
+// owner, at any time, most commonly when the object is about to be deleted.
+
+// Weak pointers are useful when an object needs to be accessed safely by one
+// or more objects other than its owner, and those callers can cope with the
+// object vanishing and e.g. tasks posted to it being silently dropped.
+// Reference-counting such an object would complicate the ownership graph and
+// make it harder to reason about the object's lifetime.
+
+// EXAMPLE:
+//
+// class Controller {
+// public:
+// Controller() : weak_factory_(this) {}
+// void SpawnWorker() { Worker::StartNew(weak_factory_.GetWeakPtr()); }
+// void WorkComplete(const Result& result) { ... }
+// private:
+// // Member variables should appear before the WeakPtrFactory, to ensure
+// // that any WeakPtrs to Controller are invalidated before its members
+// // variable's destructors are executed, rendering them invalid.
+// WeakPtrFactory<Controller> weak_factory_;
+// };
+//
+// class Worker {
+// public:
+// static void StartNew(const WeakPtr<Controller>& controller) {
+// Worker* worker = new Worker(controller);
+// // Kick off asynchronous processing...
+// }
+// private:
+// Worker(const WeakPtr<Controller>& controller)
+// : controller_(controller) {}
+// void DidCompleteAsynchronousProcessing(const Result& result) {
+// if (controller_)
+// controller_->WorkComplete(result);
+// }
+// WeakPtr<Controller> controller_;
+// };
+//
+// With this implementation a caller may use SpawnWorker() to dispatch multiple
+// Workers and subsequently delete the Controller, without waiting for all
+// Workers to have completed.
+
+// ------------------------- IMPORTANT: Thread-safety -------------------------
+
+// Weak pointers may be passed safely between threads, but must always be
+// dereferenced and invalidated on the same TaskQueue or thread, otherwise
+// checking the pointer would be racey.
+//
+// To ensure correct use, the first time a WeakPtr issued by a WeakPtrFactory
+// is dereferenced, the factory and its WeakPtrs become bound to the calling
+// TaskQueue/thread, and cannot be dereferenced or
+// invalidated on any other TaskQueue/thread. Bound WeakPtrs can still be handed
+// off to other TaskQueues, e.g. to use to post tasks back to object on the
+// bound sequence.
+//
+// Thus, at least one WeakPtr object must exist and have been dereferenced on
+// the correct thread to enforce that other WeakPtr objects will enforce they
+// are used on the desired thread.
+
+namespace rtc {
+
+namespace internal {
+
+class WeakReference {
+ public:
+ // Although Flag is bound to a specific sequence, it may be
+ // deleted from another via base::WeakPtr::~WeakPtr().
+ class Flag : public RefCountInterface {
+ public:
+ Flag();
+
+ void Invalidate();
+ bool IsValid() const;
+
+ private:
+ friend class RefCountedObject<Flag>;
+
+ ~Flag() override;
+
+ SequencedTaskChecker checker_;
+ bool is_valid_;
+ };
+
+ WeakReference();
+ explicit WeakReference(const Flag* flag);
+ ~WeakReference();
+
+ WeakReference(WeakReference&& other);
+ WeakReference(const WeakReference& other);
+ WeakReference& operator=(WeakReference&& other) = default;
+ WeakReference& operator=(const WeakReference& other) = default;
+
+ bool is_valid() const;
+
+ private:
+ scoped_refptr<const Flag> flag_;
+};
+
+class WeakReferenceOwner {
+ public:
+ WeakReferenceOwner();
+ ~WeakReferenceOwner();
+
+ WeakReference GetRef() const;
+
+ bool HasRefs() const { return flag_.get() && !flag_->HasOneRef(); }
+
+ void Invalidate();
+
+ private:
+ SequencedTaskChecker checker_;
+ mutable scoped_refptr<RefCountedObject<WeakReference::Flag>> flag_;
+};
+
+// This class simplifies the implementation of WeakPtr's type conversion
+// constructor by avoiding the need for a public accessor for ref_. A
+// WeakPtr<T> cannot access the private members of WeakPtr<U>, so this
+// base class gives us a way to access ref_ in a protected fashion.
+class WeakPtrBase {
+ public:
+ WeakPtrBase();
+ ~WeakPtrBase();
+
+ WeakPtrBase(const WeakPtrBase& other) = default;
+ WeakPtrBase(WeakPtrBase&& other) = default;
+ WeakPtrBase& operator=(const WeakPtrBase& other) = default;
+ WeakPtrBase& operator=(WeakPtrBase&& other) = default;
+
+ protected:
+ explicit WeakPtrBase(const WeakReference& ref);
+
+ WeakReference ref_;
+};
+
+} // namespace internal
+
+template <typename T>
+class WeakPtrFactory;
+
+template <typename T>
+class WeakPtr : public internal::WeakPtrBase {
+ public:
+ WeakPtr() : ptr_(nullptr) {}
+
+ // Allow conversion from U to T provided U "is a" T. Note that this
+ // is separate from the (implicit) copy and move constructors.
+ template <typename U>
+ WeakPtr(const WeakPtr<U>& other)
+ : internal::WeakPtrBase(other), ptr_(other.ptr_) {}
+ template <typename U>
+ WeakPtr(WeakPtr<U>&& other)
+ : internal::WeakPtrBase(std::move(other)), ptr_(other.ptr_) {}
+
+ T* get() const { return ref_.is_valid() ? ptr_ : nullptr; }
+
+ T& operator*() const {
+ RTC_DCHECK(get() != nullptr);
+ return *get();
+ }
+ T* operator->() const {
+ RTC_DCHECK(get() != nullptr);
+ return get();
+ }
+
+ void reset() {
+ ref_ = internal::WeakReference();
+ ptr_ = nullptr;
+ }
+
+ // Allow conditionals to test validity, e.g. if (weak_ptr) {...};
+ explicit operator bool() const { return get() != nullptr; }
+
+ private:
+ template <typename U>
+ friend class WeakPtr;
+ friend class WeakPtrFactory<T>;
+
+ WeakPtr(const internal::WeakReference& ref, T* ptr)
+ : internal::WeakPtrBase(ref), ptr_(ptr) {}
+
+ // This pointer is only valid when ref_.is_valid() is true. Otherwise, its
+ // value is undefined (as opposed to nullptr).
+ T* ptr_;
+};
+
+// Allow callers to compare WeakPtrs against nullptr to test validity.
+template <class T>
+bool operator!=(const WeakPtr<T>& weak_ptr, std::nullptr_t) {
+ return !(weak_ptr == nullptr);
+}
+template <class T>
+bool operator!=(std::nullptr_t, const WeakPtr<T>& weak_ptr) {
+ return weak_ptr != nullptr;
+}
+template <class T>
+bool operator==(const WeakPtr<T>& weak_ptr, std::nullptr_t) {
+ return weak_ptr.get() == nullptr;
+}
+template <class T>
+bool operator==(std::nullptr_t, const WeakPtr<T>& weak_ptr) {
+ return weak_ptr == nullptr;
+}
+
+// A class may be composed of a WeakPtrFactory and thereby
+// control how it exposes weak pointers to itself. This is helpful if you only
+// need weak pointers within the implementation of a class. This class is also
+// useful when working with primitive types. For example, you could have a
+// WeakPtrFactory<bool> that is used to pass around a weak reference to a bool.
+
+// Note that GetWeakPtr must be called on one and only one TaskQueue or thread
+// and the WeakPtr must only be dereferenced and invalidated on that same
+// TaskQueue/thread. A WeakPtr instance can be copied and posted to other
+// sequences though as long as it is not dereferenced (WeakPtr<T>::get()).
+template <class T>
+class WeakPtrFactory {
+ public:
+ explicit WeakPtrFactory(T* ptr) : ptr_(ptr) {}
+
+ ~WeakPtrFactory() { ptr_ = nullptr; }
+
+ WeakPtr<T> GetWeakPtr() {
+ RTC_DCHECK(ptr_);
+ return WeakPtr<T>(weak_reference_owner_.GetRef(), ptr_);
+ }
+
+ // Call this method to invalidate all existing weak pointers.
+ void InvalidateWeakPtrs() {
+ RTC_DCHECK(ptr_);
+ weak_reference_owner_.Invalidate();
+ }
+
+ // Call this method to determine if any weak pointers exist.
+ bool HasWeakPtrs() const {
+ RTC_DCHECK(ptr_);
+ return weak_reference_owner_.HasRefs();
+ }
+
+ private:
+ internal::WeakReferenceOwner weak_reference_owner_;
+ T* ptr_;
+ RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(WeakPtrFactory);
+};
+
+} // namespace rtc
#endif // WEBRTC_BASE_WEAK_PTR_H_
