gecko-dev/xpcom/glue/nsArrayEnumerator.cpp

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/* 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/. */

#include "mozilla/Attributes.h"

#include "nsArrayEnumerator.h"

#include "nsIArray.h"
#include "nsISimpleEnumerator.h"

#include "nsCOMArray.h"
#include "nsCOMPtr.h"

class nsSimpleArrayEnumerator MOZ_FINAL : public nsISimpleEnumerator
{
public:
    // nsISupports interface
    NS_DECL_ISUPPORTS

    // nsISimpleEnumerator interface
    NS_DECL_NSISIMPLEENUMERATOR

    // nsSimpleArrayEnumerator methods
    nsSimpleArrayEnumerator(nsIArray* aValueArray) :
        mValueArray(aValueArray), mIndex(0) {
    }

private:
    ~nsSimpleArrayEnumerator() {}

protected:
    nsCOMPtr<nsIArray> mValueArray;
    uint32_t mIndex;
};

NS_IMPL_ISUPPORTS1(nsSimpleArrayEnumerator, nsISimpleEnumerator)

NS_IMETHODIMP
nsSimpleArrayEnumerator::HasMoreElements(bool* aResult)
{
    NS_PRECONDITION(aResult != 0, "null ptr");
    if (! aResult)
        return NS_ERROR_NULL_POINTER;

    if (!mValueArray) {
        *aResult = false;
        return NS_OK;
    }

    uint32_t cnt;
    nsresult rv = mValueArray->GetLength(&cnt);
    if (NS_FAILED(rv)) return rv;
    *aResult = (mIndex < cnt);
    return NS_OK;
}

NS_IMETHODIMP
nsSimpleArrayEnumerator::GetNext(nsISupports** aResult)
{
    NS_PRECONDITION(aResult != 0, "null ptr");
    if (! aResult)
        return NS_ERROR_NULL_POINTER;

    if (!mValueArray) {
        *aResult = nullptr;
        return NS_OK;
    }

    uint32_t cnt;
    nsresult rv = mValueArray->GetLength(&cnt);
    if (NS_FAILED(rv)) return rv;
    if (mIndex >= cnt)
        return NS_ERROR_UNEXPECTED;

    return mValueArray->QueryElementAt(mIndex++, NS_GET_IID(nsISupports), (void**)aResult);
}

nsresult
NS_NewArrayEnumerator(nsISimpleEnumerator* *result,
                      nsIArray* array)
{
    nsSimpleArrayEnumerator* enumer = new nsSimpleArrayEnumerator(array);
    if (enumer == nullptr)
        return NS_ERROR_OUT_OF_MEMORY;

    NS_ADDREF(*result = enumer);
    return NS_OK;
}

////////////////////////////////////////////////////////////////////////////////

// enumerator implementation for nsCOMArray
// creates a snapshot of the array in question
// you MUST use NS_NewArrayEnumerator to create this, so that
// allocation is done correctly
class nsCOMArrayEnumerator MOZ_FINAL : public nsISimpleEnumerator
{
public:
    // nsISupports interface
    NS_DECL_ISUPPORTS

    // nsISimpleEnumerator interface
    NS_DECL_NSISIMPLEENUMERATOR

    // nsSimpleArrayEnumerator methods
    nsCOMArrayEnumerator() : mIndex(0) {
    }

    // specialized operator to make sure we make room for mValues
    void* operator new (size_t size, const nsCOMArray_base& aArray) CPP_THROW_NEW;
    void operator delete(void* ptr) {
        ::operator delete(ptr);
    }

private:
    ~nsCOMArrayEnumerator(void);

protected:
    uint32_t mIndex;            // current position
    uint32_t mArraySize;        // size of the array
    
    // this is actually bigger
    nsISupports* mValueArray[1];
};

NS_IMPL_ISUPPORTS1(nsCOMArrayEnumerator, nsISimpleEnumerator)

nsCOMArrayEnumerator::~nsCOMArrayEnumerator()
{
    // only release the entries that we haven't visited yet
    for (; mIndex < mArraySize; ++mIndex) {
        NS_IF_RELEASE(mValueArray[mIndex]);
    }
}

NS_IMETHODIMP
nsCOMArrayEnumerator::HasMoreElements(bool* aResult)
{
    NS_PRECONDITION(aResult != 0, "null ptr");
    if (! aResult)
        return NS_ERROR_NULL_POINTER;

    *aResult = (mIndex < mArraySize);
    return NS_OK;
}

NS_IMETHODIMP
nsCOMArrayEnumerator::GetNext(nsISupports** aResult)
{
    NS_PRECONDITION(aResult != 0, "null ptr");
    if (! aResult)
        return NS_ERROR_NULL_POINTER;

    if (mIndex >= mArraySize)
        return NS_ERROR_UNEXPECTED;

    // pass the ownership of the reference to the caller. Since
    // we AddRef'ed during creation of |this|, there is no need
    // to AddRef here
    *aResult = mValueArray[mIndex++];

    // this really isn't necessary. just pretend this happens, since
    // we'll never visit this value again!
    // mValueArray[(mIndex-1)] = nullptr;
    
    return NS_OK;
}

void*
nsCOMArrayEnumerator::operator new (size_t size, const nsCOMArray_base& aArray)
    CPP_THROW_NEW
{
    // create enough space such that mValueArray points to a large
    // enough value. Note that the initial value of size gives us
    // space for mValueArray[0], so we must subtract
    size += (aArray.Count() - 1) * sizeof(aArray[0]);

    // do the actual allocation
    nsCOMArrayEnumerator * result =
        static_cast<nsCOMArrayEnumerator*>(::operator new(size));
    NS_ENSURE_TRUE(result, nullptr);

    // now need to copy over the values, and addref each one
    // now this might seem like a lot of work, but we're actually just
    // doing all our AddRef's ahead of time since GetNext() doesn't
    // need to AddRef() on the way out
    uint32_t i;
    uint32_t max = result->mArraySize = aArray.Count();
    for (i = 0; i<max; i++) {
        result->mValueArray[i] = aArray[i];
        NS_IF_ADDREF(result->mValueArray[i]);
    }

    return result;
}

nsresult
NS_NewArrayEnumerator(nsISimpleEnumerator* *aResult,
                      const nsCOMArray_base& aArray)
{
    nsCOMArrayEnumerator *enumerator = new (aArray) nsCOMArrayEnumerator();
    if (!enumerator) return NS_ERROR_OUT_OF_MEMORY;

    NS_ADDREF(*aResult = enumerator);
    return NS_OK;
}