constructor(readable, bufferSize, maxBuffers, outgoingHandler, concurrency, encoding) {
        /**
         * An internal event emitter.
         */
        this.emitter = new events.EventEmitter();
        /**
         * An internal offset marker to track data offset in bytes of next outgoingHandler.
         */
        this.offset = 0;
        /**
         * An internal marker to track whether stream is end.
         */
        this.isStreamEnd = false;
        /**
         * An internal marker to track whether stream or outgoingHandler returns error.
         */
        this.isError = false;
        /**
         * How many handlers are executing.
         */
        this.executingOutgoingHandlers = 0;
        /**
         * How many buffers have been allocated.
         */
        this.numBuffers = 0;
        /**
         * Because this class doesn't know how much data every time stream pops, which
         * is defined by highWaterMarker of the stream. So BufferScheduler will cache
         * data received from the stream, when data in unresolvedDataArray exceeds the
         * blockSize defined, it will try to concat a blockSize of buffer, fill into available
         * buffers from incoming and push to outgoing array.
         */
        this.unresolvedDataArray = [];
        /**
         * How much data consisted in unresolvedDataArray.
         */
        this.unresolvedLength = 0;
        /**
         * The array includes all the available buffers can be used to fill data from stream.
         */
        this.incoming = [];
        /**
         * The array (queue) includes all the buffers filled from stream data.
         */
        this.outgoing = [];
        if (bufferSize <= 0) {
            throw new RangeError(`bufferSize must be larger than 0, current is ${bufferSize}`);
        }
        if (maxBuffers <= 0) {
            throw new RangeError(`maxBuffers must be larger than 0, current is ${maxBuffers}`);
        }
        if (concurrency <= 0) {
            throw new RangeError(`concurrency must be larger than 0, current is ${concurrency}`);
        }
        this.bufferSize = bufferSize;
        this.maxBuffers = maxBuffers;
        this.readable = readable;
        this.outgoingHandler = outgoingHandler;
        this.concurrency = concurrency;
        this.encoding = encoding;
    }
Creates an instance of BufferScheduler.

@param readable - A Node.js Readable stream
@param bufferSize - Buffer size of every maintained buffer
@param maxBuffers - How many buffers can be allocated
@param outgoingHandler - An async function scheduled to be
                                         triggered when a buffer fully filled
                                         with stream data
@param concurrency - Concurrency of executing outgoingHandlers (>0)
@param encoding - [Optional] Encoding of Readable stream when it's a string stream