SkWeakRefCnt Class Reference

#include <SkWeakRefCnt.h>

Inheritance diagram for SkWeakRefCnt:

Public Member Functions
	SkWeakRefCnt ()
	~SkWeakRefCnt () override
bool	try_ref () const
void	weak_ref () const
void	weak_unref () const
bool	weak_expired () const
Public Member Functions inherited from SkRefCntBase
	SkRefCntBase ()
virtual	~SkRefCntBase ()
bool	unique () const
void	ref () const
void	unref () const

Protected Member Functions
virtual void	weak_dispose () const

Private Member Functions
void	internal_dispose () const override

Detailed Description

SkWeakRefCnt is the base class for objects that may be shared by multiple objects. When an existing strong owner wants to share a reference, it calls ref(). When a strong owner wants to release its reference, it calls unref(). When the shared object's strong reference count goes to zero as the result of an unref() call, its (virtual) weak_dispose method is called. It is an error for the destructor to be called explicitly (or via the object going out of scope on the stack or calling delete) if getRefCnt() > 1.

In addition to strong ownership, an owner may instead obtain a weak reference by calling weak_ref(). A call to weak_ref() must be balanced by a call to weak_unref(). To obtain a strong reference from a weak reference, call try_ref(). If try_ref() returns true, the owner's pointer is now also a strong reference on which unref() must be called. Note that this does not affect the original weak reference, weak_unref() must still be called. When the weak reference count goes to zero, the object is deleted. While the weak reference count is positive and the strong reference count is zero the object still exists, but will be in the disposed state. It is up to the object to define what this means.

Note that a strong reference implicitly implies a weak reference. As a result, it is allowable for the owner of a strong ref to call try_ref(). This will have the same effect as calling ref(), but may be more expensive.

Example:

SkWeakRefCnt myRef = strongRef.weak_ref(); ... // strongRef.unref() may or may not be called if (myRef.try_ref()) { ... // use myRef myRef.unref(); } else { myRef is in the disposed state } myRef.weak_unref();

Definition at line 55 of file SkWeakRefCnt.h.

Constructor & Destructor Documentation

SkWeakRefCnt()

SkWeakRefCnt::SkWeakRefCnt ( )

inline

Default construct, initializing the reference counts to 1. The strong references collectively hold one weak reference. When the strong reference count goes to zero, the collectively held weak reference is released.

Definition at line 62 of file SkWeakRefCnt.h.

: SkRefCnt(), fWeakCnt(1) {}

~SkWeakRefCnt()

SkWeakRefCnt::~SkWeakRefCnt ( )

inlineoverride

Destruct, asserting that the weak reference count is 1.

Definition at line 66 of file SkWeakRefCnt.h.

                             {
#ifdef SK_DEBUG
        SkASSERT(getWeakCnt() == 1);
        fWeakCnt.store(0, std::memory_order_relaxed);
#endif
    }

Member Function Documentation

internal_dispose()

void SkWeakRefCnt::internal_dispose ( ) const

inlineoverrideprivatevirtual

Called when the strong reference count goes to zero. Calls weak_dispose on the object and releases the implicit weak reference held collectively by the strong references.

Reimplemented from SkRefCntBase.

Definition at line 162 of file SkWeakRefCnt.h.

                                           {
        weak_dispose();
        weak_unref();
    }

try_ref()

bool SkWeakRefCnt::try_ref ( ) const

inline

Creates a strong reference from a weak reference, if possible. The caller must already be an owner. If try_ref() returns true the owner is in posession of an additional strong reference. Both the original reference and new reference must be properly unreferenced. If try_ref() returns false, no strong reference could be created and the owner's reference is in the same state as before the call.

Definition at line 103 of file SkWeakRefCnt.h.

                                       {
        if (atomic_conditional_acquire_strong_ref() != 0) {
            // Acquire barrier (L/SL), if not provided above.
            // Prevents subsequent code from happening before the increment.
            return true;
        }
        return false;
    }

weak_dispose()

virtual void SkWeakRefCnt::weak_dispose ( ) const

inlineprotectedvirtual

Called when the strong reference count goes to zero. This allows the object to free any resources it may be holding. Weak references may still exist and their level of allowed access to the object is defined by the object's class.

Reimplemented in DWriteFontTypeface.

Definition at line 154 of file SkWeakRefCnt.h.

                                      {
    }

weak_expired()

bool SkWeakRefCnt::weak_expired ( ) const

inline

Returns true if there are no strong references to the object. When this is the case all future calls to try_ref() will return false.

Definition at line 144 of file SkWeakRefCnt.h.

                              {
        return fRefCnt.load(std::memory_order_relaxed) == 0;
    }

weak_ref()

void SkWeakRefCnt::weak_ref ( ) const

inline

Increment the weak reference count. Must be balanced by a call to weak_unref().

Definition at line 115 of file SkWeakRefCnt.h.

                          {
        SkASSERT(getRefCnt() > 0);
        SkASSERT(getWeakCnt() > 0);
        // No barrier required.
        (void)fWeakCnt.fetch_add(+1, std::memory_order_relaxed);
    }

weak_unref()

void SkWeakRefCnt::weak_unref ( ) const

inline

Decrement the weak reference count. If the weak reference count is 1 before the decrement, then call delete on the object. Note that if this is the case, then the object needs to have been allocated via new, and not on the stack.

Definition at line 127 of file SkWeakRefCnt.h.

                            {
        SkASSERT(getWeakCnt() > 0);
        // A release here acts in place of all releases we "should" have been doing in ref().
        if (1 == fWeakCnt.fetch_add(-1, std::memory_order_acq_rel)) {
            // Like try_ref(), the acquire is only needed on success, to make sure
            // code in internal_dispose() doesn't happen before the decrement.
#ifdef SK_DEBUG
            // so our destructor won't complain
            fWeakCnt.store(1, std::memory_order_relaxed);
#endif
            this->INHERITED::internal_dispose();
        }
    }

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The documentation for this class was generated from the following file:

• third_party/skia/include/private/SkWeakRefCnt.h