c# - While loop Does not finish even when statement goes false -

i'm writing winform application control encoder engine via serial port. protocol quite simple, send 1st command ask engine moving, , 2nd command confirm it's been in new position, , on other places. here code this:

string dataread =""; serialport1.write("p.1=2950\r\n"); //location register (2950) serialport1.write("^.1\r\n"); //moving command  while (dataread.contains("px.1=2950") == false) {    serialport1.write("?96.1\r\n"); //ask current location    respond3 = serialport1.readexisting();    dataread = string.concat(dataread, respond3);  } //keep moving 710 after stop @ 2950 serialport1.write("p.1=710\r\n"); //location register (710) serialport1.write("^.1\r\n"); //moving command 

the problem is, when debug app, it's stuck in while-loop. if break all, , continue again, pass. respond3 used output engine. whenever gets correct respond, while-loop finish.

the problem code how readexisting works. important part is:

reads immediately available bytes, based on encoding, in both stream , input buffer of serialport object.

emphasis mine.

when you're debugging, io port has more time read data, you'll long string in input so:

"?96.1\r\n?96.1\r\n?96.1\r\n?96.1\r\npx.1=2950\r\n"

however, when you're not debugging code runs faster, , get: "?" followed "9" etc.

as such immediately available string never match string "px.1=2950" , loop never stop.

what want use, given newline delimited string using, readline method.