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POOSX Serial read freeze / hang
 

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    <p>I'm writing a serial communication wrapper class in Objective-C. To list all serial available modems and setup the connection I'm using pretty much the same code as used in <a href="https://developer.apple.com/library/mac/documentation/DeviceDrivers/Conceptual/WorkingWSerial/WWSerial_SerialDevs/SerialDevices.html#//apple_ref/doc/uid/TP30000384-TPXREF119" rel="nofollow">this example project by Apple</a>.</p> <p>I could read and write the ways apple does it. But I want to implement a loop on a second thread and write to the stream if a <code>NSString *writeString</code> longer 0 and read after write if bytes are available.</p> <p>I got writing working quite straight forward. I just used the <code>write</code> function declared in <code>unistd.h</code>.</p> <p>Reading will not work. Whenever I call <code>read()</code>, the function hangs and my loop does not proceed.</p> <p>Here is the code used in my loop:</p> <pre><code>- (void)runInCOMLoop { do { // write } while (bytesWritten &lt; strlen([_writeString UTF8String])); NSMutableString *readString = [NSMutableString string]; ssize_t bytesRead = 0; ssize_t readB = 0; char buffer[256]; do { readB = read(_fileDescriptor, &amp;buffer, sizeof(buffer)); // ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ this function hangs bytesRead += readB; if (readB == -1 { // error } else if (readB &gt; 0) { if(buffer[bytesRead - 1] == '\r' ]] buffer[bytesRead - 1] == '\n') { break; } [readString appendString:[NSString stringWithUTF8String:buffer]]; } } while (readB &gt; 0); </code></pre> <p>What am I doing wrong here?</p>
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    1. USAndrew Madsen
    1. USJulian F. Weinert
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      1. USMartin James
 

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