android分析之智能指针

// ---------------------------------------------------------------------------

class RefBase::weakref_impl : public RefBase::weakref_type//引用计数器的实现类
{
public:
    volatile int32_t    mStrong;//强引用
    volatile int32_t    mWeak;//若引用
    RefBase* const      mBase;
    volatile int32_t    mFlags;

#if !DEBUG_REFS

    weakref_impl(RefBase* base)
        : mStrong(INITIAL_STRONG_VALUE)
        , mWeak(0)
        , mBase(base)
        , mFlags(0)
    {
    }

    void addStrongRef(const void* /*id*/) { }
    void removeStrongRef(const void* /*id*/) { }
    void renameStrongRefId(const void* /*old_id*/, const void* /*new_id*/) { }
    void addWeakRef(const void* /*id*/) { }
    void removeWeakRef(const void* /*id*/) { }
    void renameWeakRefId(const void* /*old_id*/, const void* /*new_id*/) { }
    void printRefs() const { }
    void trackMe(bool, bool) { }

#else

    weakref_impl(RefBase* base)
        : mStrong(INITIAL_STRONG_VALUE)
        , mWeak(0)
        , mBase(base)
        , mFlags(0)
        , mStrongRefs(NULL)
        , mWeakRefs(NULL)
        , mTrackEnabled(!!DEBUG_REFS_ENABLED_BY_DEFAULT)
        , mRetain(false)
    {
    }
    
    ~weakref_impl()
    {
        bool dumpStack = false;
        if (!mRetain && mStrongRefs != NULL) {
            dumpStack = true;
#if DEBUG_REFS_FATAL_SANITY_CHECKS
            LOG_ALWAYS_FATAL("Strong references remain!");
#else
            ALOGE("Strong references remain:");
#endif
            ref_entry* refs = mStrongRefs;
            while (refs) {
                char inc = refs->ref >= 0 ? ‘+‘ : ‘-‘;
                ALOGD("\t%c ID %p (ref %d):", inc, refs->id, refs->ref);
#if DEBUG_REFS_CALLSTACK_ENABLED
                refs->stack.dump();
#endif
                refs = refs->next;
            }
        }

        if (!mRetain && mWeakRefs != NULL) {
            dumpStack = true;
#if DEBUG_REFS_FATAL_SANITY_CHECKS
            LOG_ALWAYS_FATAL("Weak references remain:");
#else
            ALOGE("Weak references remain!");
#endif
            ref_entry* refs = mWeakRefs;
            while (refs) {
                char inc = refs->ref >= 0 ? ‘+‘ : ‘-‘;
                ALOGD("\t%c ID %p (ref %d):", inc, refs->id, refs->ref);
#if DEBUG_REFS_CALLSTACK_ENABLED
                refs->stack.dump();
#endif
                refs = refs->next;
            }
        }
        if (dumpStack) {
            ALOGE("above errors at:");
            CallStack stack;
            stack.update();
            stack.dump();
        }
    }

    void addStrongRef(const void* id) {
        //ALOGD_IF(mTrackEnabled,
        //        "addStrongRef: RefBase=%p, id=%p", mBase, id);
        addRef(&mStrongRefs, id, mStrong);
    }

    void removeStrongRef(const void* id) {
        //ALOGD_IF(mTrackEnabled,
        //        "removeStrongRef: RefBase=%p, id=%p", mBase, id);
        if (!mRetain) {
            removeRef(&mStrongRefs, id);
        } else {
            addRef(&mStrongRefs, id, -mStrong);
        }
    }

    void renameStrongRefId(const void* old_id, const void* new_id) {
        //ALOGD_IF(mTrackEnabled,
        //        "renameStrongRefId: RefBase=%p, oid=%p, nid=%p",
        //        mBase, old_id, new_id);
        renameRefsId(mStrongRefs, old_id, new_id);
    }

    void addWeakRef(const void* id) {
        addRef(&mWeakRefs, id, mWeak);
    }

    void removeWeakRef(const void* id) {
        if (!mRetain) {
            removeRef(&mWeakRefs, id);
        } else {
            addRef(&mWeakRefs, id, -mWeak);
        }
    }

    void renameWeakRefId(const void* old_id, const void* new_id) {
        renameRefsId(mWeakRefs, old_id, new_id);
    }

    void trackMe(bool track, bool retain)
    { 
        mTrackEnabled = track;
        mRetain = retain;
    }

    void printRefs() const
    {
        String8 text;

        {
            Mutex::Autolock _l(mMutex);
            char buf[128];
            sprintf(buf, "Strong references on RefBase %p (weakref_type %p):\n", mBase, this);
            text.append(buf);
            printRefsLocked(&text, mStrongRefs);
            sprintf(buf, "Weak references on RefBase %p (weakref_type %p):\n", mBase, this);
            text.append(buf);
            printRefsLocked(&text, mWeakRefs);
        }

        {
            char name[100];
            snprintf(name, 100, "/data/%p.stack", this);
            int rc = open(name, O_RDWR | O_CREAT | O_APPEND);
            if (rc >= 0) {
                write(rc, text.string(), text.length());
                close(rc);
                ALOGD("STACK TRACE for %p saved in %s", this, name);
            }
            else ALOGE("FAILED TO PRINT STACK TRACE for %p in %s: %s", this,
                      name, strerror(errno));
        }
    }

private:
    struct ref_entry
    {
        ref_entry* next;
        const void* id;
#if DEBUG_REFS_CALLSTACK_ENABLED
        CallStack stack;
#endif
        int32_t ref;
    };

    void addRef(ref_entry** refs, const void* id, int32_t mRef)
    {
        if (mTrackEnabled) {
            AutoMutex _l(mMutex);

            ref_entry* ref = new ref_entry;
            // Reference count at the time of the snapshot, but before the
            // update.  Positive value means we increment, negative--we
            // decrement the reference count.
            ref->ref = mRef;
            ref->id = id;
#if DEBUG_REFS_CALLSTACK_ENABLED
            ref->stack.update(2);
#endif
            ref->next = *refs;
            *refs = ref;
        }
    }

    void removeRef(ref_entry** refs, const void* id)
    {
        if (mTrackEnabled) {
            AutoMutex _l(mMutex);
            
            ref_entry* const head = *refs;
            ref_entry* ref = head;
            while (ref != NULL) {
                if (ref->id == id) {
                    *refs = ref->next;
                    delete ref;
                    return;
                }
                refs = &ref->next;
                ref = *refs;
            }

#if DEBUG_REFS_FATAL_SANITY_CHECKS
            LOG_ALWAYS_FATAL("RefBase: removing id %p on RefBase %p"
                    "(weakref_type %p) that doesn‘t exist!",
                    id, mBase, this);
#endif

            ALOGE("RefBase: removing id %p on RefBase %p"
                    "(weakref_type %p) that doesn‘t exist!",
                    id, mBase, this);

            ref = head;
            while (ref) {
                char inc = ref->ref >= 0 ? ‘+‘ : ‘-‘;
                ALOGD("\t%c ID %p (ref %d):", inc, ref->id, ref->ref);
                ref = ref->next;
            }

            CallStack stack;
            stack.update();
            stack.dump();
        }
    }

    void renameRefsId(ref_entry* r, const void* old_id, const void* new_id)
    {
        if (mTrackEnabled) {
            AutoMutex _l(mMutex);
            ref_entry* ref = r;
            while (ref != NULL) {
                if (ref->id == old_id) {
                    ref->id = new_id;
                }
                ref = ref->next;
            }
        }
    }

    void printRefsLocked(String8* out, const ref_entry* refs) const
    {
        char buf[128];
        while (refs) {
            char inc = refs->ref >= 0 ? ‘+‘ : ‘-‘;
            sprintf(buf, "\t%c ID %p (ref %d):\n", 
                    inc, refs->id, refs->ref);
            out->append(buf);
#if DEBUG_REFS_CALLSTACK_ENABLED
            out->append(refs->stack.toString("\t\t"));
#else
            out->append("\t\t(call stacks disabled)");
#endif
            refs = refs->next;
        }
    }

    mutable Mutex mMutex;
    ref_entry* mStrongRefs;
    ref_entry* mWeakRefs;

    bool mTrackEnabled;
    // Collect stack traces on addref and removeref, instead of deleting the stack references
    // on removeref that match the address ones.
    bool mRetain;

#endif
};