After every Enqueue() all the values in the Queue become the same

问题

I'm receiving some data over a socket and trying to add it to a Queue so it can be dequeued by another thread that is much more slow, something like a buffer.

The problem is that everytime I enqueue a new value, all the values in the queue become that.

                    byte[] aux = new byte[1464];
                    aux = (byte[])ar.AsyncState;

                    //add the package to the package fifo list
                    lock (lockPktBuffer)
                    {
                        packetBuffer.Enqueue(aux);
                    }

First I thought that I was passing a pointer, so all the entries are just pointing to the same variable.

So I tried to do this:

                    lock (lockPktBuffer)
                    {
                        packetBuffer.Enqueue((byte[])ar.AsyncState);
                    }

But got the same problem.

Any ideia how to work this out ?

回答1:

Here is what's going on (see the comments):

// This line creates a new array
byte[] aux = new byte[1464];
// This line "forgets" the new array, and replaces it with ar.AsyncState: 
aux = (byte[])ar.AsyncState;

As the result of this, all additions to the queue happen to enqueue the same object returned from ar.AsyncState, producing the effect that you see (all instances in the queue look the same).

Here is how you can fix it:

byte[] aux = ((byte[])(ar.AsyncState).ToArray();
...
packetBuffer.Enqueue(aux);

This call makes a copy of ar.AsyncState into a new array of bytes, making sure that all instances that you enqueue are independent

回答2:

You are passing a reference. When you assign an array to another, it's the reference that is copied, it doesn't copy the data in the array.

To make a copy of the array you need to specifically copy the data inside it. Example:

// get the reference to the source array
byte[] source = (byte[])ar.AsyncState;
// create a new array with the same size
byte[] aux = new byte[source.Length];
// copy all the values from the source
Array.Copy(source, aux, source.Length);

来源：https://stackoverflow.com/questions/23873213/after-every-enqueue-all-the-values-in-the-queue-become-the-same

标签

pointers

queue