Restarted Process Output won't Read - c++

Question

So I made a GUI in C++ which calls a child process every time a button is clicked twice. The StandardOutput is redirected, doesn't use ShellExecute.
I made a simple dummy process to test it, let's say dummy.exe, which basically just do this :
void() {
printf("0");
}
And that's all. The process will exit itself after 0 is plotted.
The process is started when a button is clicked, which does this :
private: System::Void bt_getData_Click(System::Object^ sender, System::EventArgs^ e) {
if (bt_getData->Text == "Get Data") {
proc->Start();
bt_getData->Text = "Stop";
}
else if (bt_getData->Text == "Stop") {
bt_getData->Text = "Get Data";
}
}
Then it will read the output using the OutputDataReceived EventHandler.
The problem is when I clicked the button again, the process will be Restarted, but the GUI can't read the new Output.
Case 1 : I cancelled the output read in the OutputDataReceived EventHandler then restart the process, but the next restarted process output can't be read.
private: System::Void outputData(System::Object^ sender, System::Diagnostics::DataReceivedEventArgs^ e) {
x0 = xt;
xt += 1;
if (xt*x_scale > pb_Graph->Width) {
x0 = 0;
xt = 0;
imgTemp = gcnew Bitmap(pb_Graph->Image, 460, 460);
gpcGraph->Clear(Color::Transparent);
}
y0 = yt;
yt = Convert::ToInt16(e->Data);
ret_index++;
if (ret_index > 2047) ret_index = 0;
gpcGraph->DrawLine(greenPen,(float)x0*x_scale,pb_Graph->Height - (float)y0/y_scale - y_null,(float)xt*x_scale,pb_Graph->Height - (float)yt/y_scale - y_null);
pb_Graph->Refresh();
}
After three times restart, this error shows :
An unhandled exception of type 'System.InvalidOperationException' occurred in System.dll
Additional information: An async read operation has already been started on the stream.
Case 2 : I didn't cancel the output read. The same error with case 1 shows, but it is still understandable to me.
Case 3 : I didn't redo the BeginOutputReadLine() when restarting. The error doesn't shown, but the restarted process output can't be read.
My actual goal is to restart the process periodically using a 1 mS timer, so I tested the restart process first using button. But it seems that the newly generated output can't be read.
Any help would be appreciated :)

Answer 1

Okay... I've managed to prevent the errors using different method, which is to call
process->StandardOutput->ReadLine();
This way the async stream reading won't happen.