QQuickImageProvider::requestImage return a QImage and crash

[HelloFan]

I have a class that inherits from QQuickImageProvider and rewrote the function requestImage like below:

QImage ExportFrameImageProvider::requestImage(const QString& id, QSize*, const QSize&) {
	int64_t theID = id.toLongLong();
	qDebug() << "Try to get image: " << theID;
	if (frameImages.find(theID) != frameImages.end()) {
		QImage image = frameImages[theID];
		qDebug() << "Image size: " << image.size();
		return image;
	}
	return {};
}

And I get image in qml like this:

           Image {
                id: frameImage
                width: parent.width
                height: parent.height
                anchors.verticalCenter: parent.verticalCenter
                anchors.horizontalCenter: parent.horizontalCenter
                asynchronous: true
                cache: false
                source: "image://" + model.imageProviderName + "/" + model.currentFrame

                Component.onCompleted: {
                    let width = model.width;
                    let height = model.height;
                    if ((height / width) > (frameImage.height / frameImage.width)) {
                        frameImage.width = frameImage.height * (width / height);
                    } else if ((height / width) < (frameImage.height / frameImage.width)) {
                        frameImage.height = frameImage.width * (height / width);
                    }
                }
            }

In actual use, when qml loads and retrieves the image for the first time, a crash occurs. Then I use Visual Studio to debug, get the stack as follows:

	Qt6Guid.dll!convertARGBToARGB32PM_avx2<1>(unsigned int * buffer, const unsigned int * src, __int64 count) line 1118	C++
 	Qt6Guid.dll!fetchRGBA8888ToARGB32PM_avx2(unsigned int * buffer, const unsigned char * src, int index, int count, const QList<unsigned int> * __formal, QDitherInfo * __formal) line 1208	C++
 	Qt6Guid.dll!convert_generic::__l2::<lambda_1>::operator()(int yStart, int yEnd) line 195	C++
 	Qt6Guid.dll!convert_generic::__l25::<lambda_2>::operator()() line 218	C++
 	Qt6Guid.dll!QRunnable::QGenericRunnable::Helper<`convert_generic'::`25'::<lambda_2>>::impl(QRunnable::QGenericRunnable::HelperBase::Op op, QRunnable::QGenericRunnable::HelperBase * that, void * arg) line 73	C++
 	Qt6Cored.dll!QRunnable::QGenericRunnable::HelperBase::run() line 61	C++
 	Qt6Cored.dll!QRunnable::QGenericRunnable::run() line 33	C++
 	Qt6Cored.dll!QThreadPoolThread::run() line 70	C++
 	Qt6Cored.dll!QThreadPrivate::start(void * arg) line 272	C++
 	kernel32.dll!BaseThreadInitThunk()	unknown
 	ntdll.dll!RtlUserThreadStart()	unknown

The error message is "0x00007FFF5DA46A95 (Qt6Guid.dll)处(位于 AfterFX.exe 中)引发的异常: 0xC0000005: 读取位置 0x000002033B49A000 时发生访问冲突。"
The error message in English roughly goes like this: Exception caused at 0x000007FFF5DA46A95 (Qt6Guid. dll) in AfterFX. exe: 0xC0000005: Access conflict occurred while reading from location 0x000002033B49A000.

The code is blow:

static void convertARGBToARGB32PM_avx2(uint *buffer, const uint *src, qsizetype count)
{
    qsizetype i = 0;
    const __m256i alphaMask = _mm256_set1_epi32(0xff000000);
    const __m256i rgbaMask = _mm256_broadcastsi128_si256(_mm_setr_epi8(2, 1, 0, 3, 6, 5, 4, 7, 10, 9, 8, 11, 14, 13, 12, 15));
    const __m256i shuffleMask = _mm256_broadcastsi128_si256(_mm_setr_epi8(6, 7, 6, 7, 6, 7, 6, 7, 14, 15, 14, 15, 14, 15, 14, 15));
    const __m256i half = _mm256_set1_epi16(0x0080);
    const __m256i zero = _mm256_setzero_si256();

    for (; i < count - 7; i += 8) {
        /* crash occurs in this line */
        __m256i srcVector = _mm256_loadu_si256(reinterpret_cast<const __m256i *>(src + i));
        if (!_mm256_testz_si256(srcVector, alphaMask)) {
            // keep the two _mm_test[zc]_siXXX next to each other
            bool cf = _mm256_testc_si256(srcVector, alphaMask);
            if (RGBA)
                srcVector = _mm256_shuffle_epi8(srcVector, rgbaMask);
            if (!cf) {
                __m256i src1 = _mm256_unpacklo_epi8(srcVector, zero);
                __m256i src2 = _mm256_unpackhi_epi8(srcVector, zero);
                __m256i alpha1 = _mm256_shuffle_epi8(src1, shuffleMask);
                __m256i alpha2 = _mm256_shuffle_epi8(src2, shuffleMask);
                src1 = _mm256_mullo_epi16(src1, alpha1);
                src2 = _mm256_mullo_epi16(src2, alpha2);
                src1 = _mm256_add_epi16(src1, _mm256_srli_epi16(src1, 8));
                src2 = _mm256_add_epi16(src2, _mm256_srli_epi16(src2, 8));
                src1 = _mm256_add_epi16(src1, half);
                src2 = _mm256_add_epi16(src2, half);
                src1 = _mm256_srli_epi16(src1, 8);
                src2 = _mm256_srli_epi16(src2, 8);
                src1 = _mm256_blend_epi16(src1, alpha1, 0x88);
                src2 = _mm256_blend_epi16(src2, alpha2, 0x88);
                srcVector = _mm256_packus_epi16(src1, src2);
                _mm256_storeu_si256(reinterpret_cast<__m256i *>(buffer + i), srcVector);
            } else {
                if (buffer != src || RGBA)
                    _mm256_storeu_si256(reinterpret_cast<__m256i *>(buffer + i), srcVector);
            }
        } else {
            _mm256_storeu_si256(reinterpret_cast<__m256i *>(buffer + i), zero);
        }
    }
......
}

And the Qt version I am using is 6.8.1.

I spent several days troubleshooting this issue, but still couldn't locate the wrong place. If you know how to fix this problem, please don't hesitate to give me some advice!
Thanks a lot.

[Christian Ehrlicher]

Try it in a simple application which only tries to load the image to see if it also crashes there.
What is frameImages and how is it filled?

[HelloFan]

@Christian-Ehrlicher FrameImage is a QImage in QImage::Format_RGBA8888; The Code normally on macOS, but there is a problem on Windows

[Christian Ehrlicher]

Does your system supports avx2? Please provide a minimal compileable example to reproduce the problem. No qml needed for this I would guess.