Create an IBuffer to use with StreamSocket::OutputStream::WriteAsync

Question

Hi,

How can it create an IBuffer to use with StreamSocket::OutputStream::WriteAsyncI, i have the data i want to send in a byte array, but don't know what will be the efficient way to pass this data to WriteAsync.

Regards,

Jose

Answer 1

Hi ,I use this code to do send data ,you can see it.

before you send data, you should make sure the connect is completed and successfully.

StreamSocket^ socket = ref new StreamSocket();

IOutputStream^ senddata = socket->OutputStream;
DatDataWriter^ writer_ = ref new DataWriter(senddata);
auto data = ref new Platform::Array<unsigned char>(size);
::memcpy(data->Data, buf, size);//buf is char* style      ( your data )
auto task1 = make_task([=] {
	try
	{
		DataWriterStoreOperation^ store_data = nullptr;
		store_data = writer_ >StoreAsync();  
		AsyncStatus storestarus = store_data->Status;
		while (storestarus != AsyncStatus::Completed)
		{	
			WaitForSingleObjectEx(_socket->smi_event_wait,2,false);//event control wait time 2 = 2ms
			storestarus = store_data->Status;
			 // here you should set wait time out to protect it can't return and blocked	
			return;

		}
		
	} 
	catch (Exception^ e)
	{
		return;
	}
	});
structured_task_group tasks;

tasks.run_and_wait(task1);

Answer 2

Hi,

After looked closer at the proposed solution i unmarked it as answer, i want to avoid the memcpy, as this is expensive operation.

Will something along this lines work?

Does it create an extra copy of the data? if so how can i avoid the extra copy?

unsinged char* data = new char[SIZE]; // Filled some where in the code.

void
write(unsigned char* data)
{
    DataWriter writer = ref new DataWriter();
    writer->WriteBytes(ref new Array<unsigned char>(data, SIZE));
    _socket->OutputStream->WriteAsync(write->DetachBuffer());
}

Regards,

Jose

Answer 3

I use memcpy() because I use the buffer is char* type.

If you use data type is defined by metro api , like IBuffer^ ,array<unsigned char>^ and so on,

you needn't use memcpy(); it's just an example.

Answer 4

I know is an example, i just was asking if there is a way that IBuffer can use the char* buffer without copy it,  an IBuffer implementation that directly writes to the char* C style buffer.

From my experiments with Platform::Array, when you pass the data, and size arguments the array ctor copy the data, so not need to explicit copy it with memcpy.

auto data = ref new Platform::Array<unsigned char>(size);
::memcpy(data->Data, buf, size);//buf is char* style      ( your data )

Will be the same as

auto data = ref new Platform::Array<unsigned char>(buf, size);

Also not sure if will be faster to use memcpy or pass the data.

Answer 5

From your code

DataWriterStoreOperation^ store_data = nullptr; 
store_data = writer_ >StoreAsync(); 
AsyncStatus storestarus = store_data->Status; 
while (storestarus != AsyncStatus::Completed) 
{ 
    WaitForSingleObjectEx(_socket->smi_event_wait,2,false);
    //event control wait time 2 = 2ms 
    storestarus = store_data->Status;
    // here you should set wait time out to protect it can't return and blocked 
    return; 
}

Seems to me that will be better to avoid while loop and use the Completed handler.

DataWriterStoreOperation^ writerResult = writer->StoreAsync();
writerResult->Completed = ref new AsyncOperationCompletedHandler<unsigned int>(
    [=](IAsyncOperation<unsigned int>^ info, Windows::Foundation::AsyncStatus status)
            {
                if(info->Status == Windows::Foundation::AsyncStatus::Error)
                {
                    // Error
                }
                else if(info->Status == Windows::Foundation::AsyncStatus::Canceled)
                {
                    // Canceled
                }
                else if(info->Status == Windows::Foundation::AsyncStatus::Completed)
                {
                    // Success
                        
                }
            });

Answer 6

Yes you code is safer, and you maybe try to find  a way that IBuffer can use the char* buffer without copy it.

if you succeed, hope you submit it to here and share it .

thank you

Answer 7

Yes i will look at this later, and i will update this thread if i found how that can be done. Thanks for the help and for take the time to look at this.