Memory is not pre-allocated in File::loadFileAsData()


Hi Jules,

when we use juce::File::loadFileAsData() to load big data, we noticed that it's much slower in version 3 than in 1.5. Turns out that the issue is in the class juce::MemoryOutputStream:

juce::File::loadFileAsData() calls juce::InputStream::readIntoMemoryBlock() with numBytes set to -1:

    return in.openedOk() && getSize() == (int64) in.readIntoMemoryBlock (destBlock);

which calls juce::MemoryOutputStream::writeFromInputStream(), again with maxNumBytesToWrite set to -1:

    MemoryOutputStream mo (block, true);
    return (size_t) mo.writeFromInputStream (*this, numBytes);

which then determines the correct amount of bytes to read, but doesn't pre-allocate it, because maxNumBytesToWrite is set to -1:

int64 MemoryOutputStream::writeFromInputStream (InputStream& source, int64 maxNumBytesToWrite)
    // before writing from an input, see if we can preallocate to make it more efficient..
    int64 availableData = source.getTotalLength() - source.getPosition();

    if (availableData > 0)
        if (maxNumBytesToWrite > availableData)
            maxNumBytesToWrite = availableData;

        if (blockToUse != nullptr)
            preallocate (blockToUse->getSize() + (size_t) maxNumBytesToWrite);

    return OutputStream::writeFromInputStream (source, maxNumBytesToWrite);


        if (maxNumBytesToWrite > availableData)


        if ((maxNumBytesToWrite > availableData) || (maxNumBytesToWrite < 0))

solves the issue.



Ah, nice one, thanks! I don't tend to load very large blocks with that so hadn't noticed, but I'll get that sorted out right away!


Awesome, thanks for the fast updates. Much appreciated!